Live by the Alternative Facts, Die by the Alternative Facts

Photo: Josh Henderson, Galveston Police Department

Sadly, it wasn’t terribly difficult to see where this story would lead. According to a May 4 post on Houston Audubon’s Facebook page, 395 birds were killed when they collided with the American National Building (Galveston’s tallest) in a storm the night before. “This is the largest event like this I have ever been a part of in over 10 years,” explained Josh Henderson, the Galveston Police supervisor who had the grim job of tallying the fatalities, in a Houston Chronicle story the next day.

And yet, it was only a matter of time (and not much of it) before the conversation shifted to… you guessed it: cats. Read more

Peter Marra: Post-Truth Pioneer

Nearly four years before the terms fake news and alternative facts made their way into common usage, there were Peter Marra’s mortality “estimates.” Developed at great expense to taxpayers, Marra’s computer-generated figures suggest that outdoor cats kill up to 4.0 billion birds annually in the 48 contiguous states. [1] Even without getting into the details, it should be obvious that the claim is simply nonsense—since the best estimates available indicate that there are only 3.2 billion birds in the continental U.S.

Nevertheless, with the publication of Cat Wars: The Devastating Consequences of a Cuddly Killer late last year, Marra doubled down on his “estimates,” making this tidy bit of fiction the centerpiece of his campaign of misinformation, scaremongering, and magical thinking.

All of that seems like a lifetime ago now—before Donald Trump became President, and, together with his largely inexperienced and woefully unprepared staff of cronies, plunged us into a Bizarro World. Up is down, black is white, right is wrong. Foreign policy is made and unmade in 140-character outbursts.

Not to be outdone, Marra’s stepped up his game—misrepresenting his own work (which, again, was junk science to begin with) and proposing a new theory of urban ecology. Read more

What’s Several Billion Birds, Among Friends?

Frequently cited estimates for birds killed by cats in the U.S. actually exceed the number of birds estimated to be in the country. Documents obtained via Freedom of Information Act raise as many questions as they answer.

As I pointed out recently, the annual mortality estimates proposed in the 2013 paper, “The impact of free-ranging domestic cats on wildlife of the United States,” don’t add up. Or, to be more precise, they do add up—and up and up. Indeed, the authors’ “conservative” estimate of birds killed by outdoor cats appear to exceed the total number of land birds estimated to be in the country.

According to the Partners In Flight Population Estimates Database—which, given its intended use for “bird-conservation planning,” would seem to be the go-to source for the best estimates available—that total is 3.2 billion. That’s only 33 percent greater than the median estimate (2.4 billion) developed by Scott Loss, Tom Will, and Peter Marra—leaving very little room for the many other sources of mortality, [1] including the 365–988 million birds they’ve estimated are killed annually as a result of building collisions. [2]

And the high-end of their “conservative” estimate of annual cat-caused mortalities (4.0 billion) actually exceeds the PIF estimate by a significant margin—raising serious questions about the validity of the work portrayed by Marra, in Cat Wars, as the culmination of a century’s worth of evidence implicating cats in the decline of birds and other wildlife. [3]

As documents obtained via Freedom of Information Act reveal, though, this isn’t the weirdest part of the story. Read more

Appealing to Our Better Nature

It’s not every day that I hear from somebody whose work I’ve criticized. (In fact, I rarely receive a response from those I reach out to for comments or clarification.) Imagine my surprise, then, when I received an e-mail from somebody involved with Nature Canada’s “cats indoors” campaign who was interested in better understanding my objections. Even more surprising was my subsequent telephone conversation with Sarah Cooper: exactly the sort of thoughtful, open exchange I’d hoped for when I launched Vox Felina six years ago today.

It doesn’t hurt that Cooper, who’s largely responsible for Nature Canada’s communication strategy for the campaign, is curious, witty, and charming.

Over the course of our conversation (nearly two hours, if I recall correctly), she gave me plenty to think about. So, to mark Vox Felina’s six-year anniversary, I want to reflect on that previous post a little bit and ask readers to weigh in as well. Read more

“Cats Indoors” Campaigns: A Grave Threat to Outdoor Cats?

In the interest of full disclosure: I keep my cats indoors 24 hours a day, seven days a week. It’s an uncompromising policy I’ve adopted for their safety — and my sanity. I encourage others to keep their cats indoors, too. Why, then, do I object so strenuously to “cats indoors” efforts, such as Nature Canada’s recently launched Keep Cats Safe and Save Bird Lives campaign?

It’s a question to which I’ve given a great deal of thought since I first began blogging about the ongoing witch-hunt against outdoor cats nearly six years ago, and it mostly comes down to the following: Read more

The (Willfully) Blind Leading the (Willfully) Blind

If the Ohio Bird Conservation Initiative truly aims to “develop management strategies that are guided by sound science,” then its recently released White Paper on Feral and Free-ranging Domestic Cats (PDF) represents a glaring and inexcusable failure. Just two sentences into the three-page paper, the self-described “coalition of 102 non-governmental organizations, governmental agencies, and businesses” [1] resorts to the familiar “kitchen sink approach,” a laundry list of (presumably) damning claims meant to substitute for a well-reasoned argument and appeal to the broadest audience possible:

“A number of peer-reviewed studies strongly suggest that large numbers of small mammals, birds, reptiles, and amphibians are killed each year by domestic cats. Additionally, cats act as reservoirs for several diseases that can sicken humans, native wildlife, and other domestic animals, such as rabies, toxoplasmosis, bartonellosis, typhus, and feline immunodeficiency virus.” [1]

One wonders what rabies, toxoplasmosis, bartonellosis, typhus, and FIV have to do with OBCI’s stated mission: “Ensuring the conservation and effective management of birds in Ohio by fostering partnerships among governmental agencies, conservation organizations, businesses, and the public”?

Nothing, really. Perhaps OBCI is expecting that nobody will notice. Read more

11 Signs of the American Bird Conservancy’s Desperate Struggle for Relevance

As most readers are undoubtedly aware, today is National Feral Cat Day. And at the risk of stating the obvious: NFCD has clearly become, to borrow a trendy phrase from social media, “a thing.” Now in its 14th year, there are hundreds of events going on around the country to mark the occasion.

All of which must be terribly frustrating for TNR-deniers. Thus, their increasingly desperate attempts to oppose, any way they can, TNR and community cat programs.

Witness, for example, Cats, Birds, and People: The Consequences of Outdoor Cats and the Need for Effective Management (PDF), a presentation by Grant Sizemore—who may or may not be the American Bird Conservancy’s Director of Invasive Species Programs. (As we’ll see shortly, it’s surprisingly complicated.)

It’s not clear exactly who these 33 slides are intended to help. After all, to anybody even remotely familiar with the issue, it’s immediately apparent that Sizemore’s claims—the “consequences” mentioned in the presentation’s title—are flimsy at best.

Equally apparent: Sizemore and ABC are not—though ABC’s been on this witch-hunt for 17 years now—about to provide any solutions.

Not only is the presentation available on ABC’s website, Sizemore’s now taking the show on the road. Last month, for example, he was in Ellenton, Florida, as part of a Coyotes and Feral Cats forum, hosted by the Suncoast Cooperative Invasive Species Management Area.

No doubt, most readers will miss such opportunities. Here, then, are 11 of the presentation’s “highlights”—my humble gift on National Feral Cat Day 2014. Read more

Tune in Sunday to Animal Wise Radio!

Tune in Sunday to Animal Wise Radio, when I’ll be on with hosts Mike Fry and Beth Nelson discussing a recently published paper declaring that “predation by house cats is probably the largest human-related source of bird mortality in Canada.”

For schedule, a list of local stations, or to listen online, check out the Animal Wise Radio website.

Research Brief: “Fearing the Feline”

Despite its dramatic-sounding conclusions, UK research into the “sub-lethal effects” of cats reveals very little about real-world predator-prey dynamics or their potential impact on bird populations.

Common blackbird. Photo courtesy of Wikimedia Commons and Andreas Trepte.

“A new study from British scientists has documented for the first time, significant new impacts to birds from outdoor cats,” announced an April 18 news release from the American Bird Conservancy, “reporting that even brief appearances of cats near avian nest sites leads to at least a doubling in lethal nest predation of eggs and young birds by third-party animals.” The study, by PhD student Colin Bonnington, Kevin J. Gaston, professor of biodiversity and conservation at the University of Exeter, and Karl L. Evans, conservation biology lecturer at the University of Sheffield (and Bonnington’s PhD advisor), was published earlier this year in the Journal of Applied Ecology as “Fearing the feline: domestic cats reduce avian fecundity through trait-mediated indirect effects that increase nest predation by other species.” Read more

Audubon Editor Suspended “Pending Further Review”

It’s been a turbulent few days for Ted Williams. First, the editors at the Orlando Sentinel—who, it seems clear, were previously asleep at the switch—revised his op-ed, pulling the comment about Tylenol and changing his affiliation from “editor-at-large for Audubon magazine” to “independent column[ist] for Audubon magazine.” They also added a disclaimer: “His views do not necessarily reflect those of the National Audubon Society.”

As of Saturday morning, Williams was more independent than ever.

That’s when the National Audubon Society announced via Facebook that the organization “suspended its contract with Mr. Williams and will remove him as ‘Editor at Large’ from the masthead pending further review.” This comes in the wake of his inflammatory op-ed in Thursday’s Orlando Sentinel in which Williams suggested that acetaminophen poisoning was one of “two effective, humane alternatives to the cat hell of TNR.”

And although Williams will likely blame his dismissal (assuming Audubon won’t just wait until the smoke clears and then quietly bring him back on board) on the “feral-cat mafia,” as he describes us in one of his online comments to the story, the fact is he’s got nobody to blame but himself. Read more

The American Bird Conservancy’s Campaign of Killing

“The only sure way to protect wildlife, cats and people is for domestic cats to be permanently removed from the outdoor environment,” argues American Bird Conservancy president George Fenwick in a Baltimore Sun op-ed published earlier this week.

“Trap-neuter-release programs that perpetuate the slaughter of wildlife and encourage the dumping of unwanted cats is [sic] a failed strategy being implemented across the United States without any consideration for environmental, human health, or animal welfare effects. It can no longer be tolerated.”

“Evidence” of the slaughter, Fenwick suggests, can be found “in a long line of scientific studies”—among them the Smithsonian/USFWS “killer cat study,” Rick Gerhold and David Jessup’s “Zoonotic Diseases” paper, Peter Marra’s gray catbird study, and Kerry Anne Loyd’s “KittyCam” research. The trouble, of course, is with the quality of Fenwick’s evidence—or in the case of Loyd’s work, how badly it’s been misrepresented by Fenwick and ABC.

But let’s face it: a witch-hunt is a much easier sell when you can put some “science” behind it. And, although too few Sun readers probably realize it, that’s exactly what Fenwick’s up to: Read more

Special Guest: Walter Lamb

Readers who follow online discussions about free-roaming cats and TNR will likely recognize Walter Lamb’s name. His comments stand out in such forums for their well-articulated, insightful, and refreshingly rational quality. Walter brings a unique perspective to these discussions, too—a bird watcher who’s used TNR to manage his neighborhood’s stray, abandoned, and feral cats.

Walter and I have communicated by e-mail for nearly 18 months now, sharing research notes and offering commentary on various news stories and research studies. In June, he contacted me with an intriguing idea for a Q&A blog post—which, I’m pleased to say, finally made it to the top of my to-do list.

Thank you, Walter, for your patience and your ongoing, thoughtful correspondence!

WL: As you know from our previous communications, I am an avid bird watcher who also used a sterilize and return approach to successfully reduce the number of homeless cats in my neighborhood from about 20 unsterilized (and reproducing) cats down to 2 remaining sterilized cats. I have been very disappointed that some wildlife conservation organizations, and many of my bird watching peers, have taken a dogmatic and moralistic approach to universally vilifying non-lethal methods of control rather than objectively analyzing all of the available science to devise pragmatic policies that can achieve the best results for wildlife in various settings.

However, I also believe that many cat advocacy groups are similarly guilty of focusing too much on talking points at the expense of objectively evaluating how they can maximize the impact of their efforts not just for cats, but for our native wildlife as well. While I understand that your blog is dedicated to protecting cats, you have always demonstrated an open mind and a willingness to consider differing perspectives. I’m hoping that you will publish the four points outlined below on your site along with your responses to them.

Population Reduction

My neighborhood project was successful because our local mentor was very blunt about the need to aggressively trap all of the unfixed cats. She didn’t sugarcoat anything or lead us to believe that just catching one or two cats was a noble effort in its own right.

I find it troubling that an organization like Alley Cat Allies doesn’t even mention population reduction in their mission statement, vision statement, or list of core values. One gets the sense from their web site that merely choosing a non-lethal approach to the problem is sufficient. I’m interested in your perspective as to why measurable and documented population reduction doesn’t seem to be more ingrained in the culture of organizations like Alley Cat Allies (or if you think it is and I’ve just missed it).

PW: Obviously, I can’t speak for Alley Cat Allies—let me see if I can address your concern from my own perspective. I am, as I think you know, a proponent of the kind of intensive sterilization effort you and your neighbors achieved. That said, I would argue that sterilizing just one or two is better than the alternative. From a population-control perspective, it’s unlikely to make a difference (unless the colony is no bigger than three or four cats), but then again, neither is having animal control haul them away to be killed. And, as you know, this is typically how such roundups go: cats are trapped only until complaints subside. At which time the remaining cats—very likely unsterilized—will continue reproducing.

And I think there’s another factor that we shouldn’t overlook or discount: people are much more likely to participate in, and support, life-saving efforts. While I agree that it’s critical to get as many cats as possible sterilized—and that this message is conveyed to anybody involved in TNR—I worry that an all-or-nothing approach will only serve to hamper any efforts to get started. In which case, the only option will be taxpayer-funded roundups—and we know how well that’s been working.

“No More Homeless Cats” vs. Homeless Cats as Critical for Ecological Balance

WL: This strikes me as an example of conflicting talking points. On the one hand, the Best Friends’ slogan seems to highlight a goal of getting cats out of the environment and into loving homes. On the other hand, defending cats’ place in the outdoors as critical for ecological balance, namely in the form of rodent control, seems to run counter to that goal.

I realize that there are examples in which the removal of cats did have unintended impacts on island ecosystems, but I’m not sure that translates to other ecosystems, especially on the mainland. I worry that this sends the wrong message to colony managers who might actually be able to achieve zero population but are given the impression that zero population is not actually a desirable goal. What is your take on this seeming contradiction?

PW: Just as I can’t speak for Alley Cat Allies, I can’t speak for Best Friends.* But, again, I’m happy to share my own thoughts. As you know, many outdoor cats are simply not adoption candidates. Many of us—including the folks at Alley Cat Allies, Best Friends, and myself—think that a fearful or unsocialized temperament is not sufficient cause for lethal control. One of the few remaining options for these cats, then, is as “working cats”—in barns, warehouses, or other environments where rodent control is desired.

Now, some argue that cats don’t actually keep down rodent numbers, and I have no first-hand experience with this myself. But as you know, cats have served this function for thousands of years now. (I’ve heard anecdotally of instances in which business owners complained of the rats and mice following the removal of cats from a particular area.)

To your more general point about cats and the environment, though—I don’t know that we’ll ever reduce the population of outdoor cats to zero across a large area (for a number of reasons). But I also don’t know that any colony managers are reducing their efforts if and when they have the opportunity to sterilize/adopt/re-home their way to zero population for a particular colony.

Feeding vs. Sterilizing

WL: It is always interesting to me that the most controversial aspect of TNR isn’t even represented in the acronym itself. I think the very different actions of sterilizing a cat and feeding a cat should be thought of separately, even if both are considered important from an animal welfare perspective. Telling someone that they shouldn’t attempt to trap and sterilize a group of cats unless they are also willing and able to feed and care for them indefinitely seems destined to suppress overall sterilization rates.

I won’t get into a detailed discussion of the pros and cons of feeding as I know you have delved into those issues in depth on your blog. What I will say is that I think that both the pros and cons of feeding are getting lost in the polarization of the discussion. I find the defense of feeding stations to be far less solid scientifically than the defense of sterilize and return itself. I was very interested in your quote of Animal People editor Merritt Clifton articulating why he opposes feeding and I hope that could be the grounds for a more thoughtful discussion of the pros and cons of various feeding practices in different settings. [Full disclosure, we fed some of our neighborhood cats on our back porch, but only after we had achieved a virtual 100 percent trap rate.]

PW: You’re absolutely right about the controversy surrounding feeding. And I agree that making sterilization efforts contingent upon a long-term caretaker commitment is counterproductive.

I know some people who, as Merritt recommends, feed only for the purposes of trapping and sterilizing. Once the cats are returned, they’re on their own. While I understand the arguments for such an approach, I think it overlooks or ignores some key advantages of ongoing feeding:

1. Regular feeding allows for ongoing monitoring for “new arrivals.” I’ve seen this first-hand, when I started feeding only one or two cats on my patio—only to have their siblings turn up soon thereafter, along with three kittens. I was able to trap and sterilize all but one adult. (I haven’t seen this cat in many months.) The kittens were all adopted. Without the daily handouts, these cats would have remained essentially invisible—and would have contributed further to the neighborhood’s population. One of my own (indoor-only) cats is another case study—had I not been feeding a small colony nearby, I never would have found, sterilized, and, ultimately, adopted him.

2. For some caretakers, regular feeding provides the opportunity to bond with the cats (even if they’ll never be able to actually touch them, as is often the case). While this factor is often dismissed by TNR opponents, I think it’s incredibly important to the ongoing effort to bring down the population of stray, abandoned, and feral cats. I think for many people, it’s this bond that keeps them involved with TNR. Take away the feeding, and you’re likely to deter such participation—and, as I think you’ll agree, we need “all hands on deck.”

[One common objection to feeding is that the food attracts wildlife that might carry rabies. In some contexts, it’s a very valid point. But again, on the whole, I think the benefits outweigh the risks. In areas where rabies among cats is more common—here in Arizona, it’s virtually unheard of—vaccinations are an integral part of most TNR programs. So the feeding and monitoring leads not only to sterilization, but also vaccination—which then serves as a kind of protective barrier between rabies in raccoons, for example, and humans.]


WL: I am aware of the herculean efforts of many cat advocates to tame and adopt the cats that they trap. Adoption to indoor only homes is the same as permanent removal from a wildlife conservation perspective and is one the best ways to achieve immediate population decline. However, when reading news coverage from different areas across the country, I very often hear the blanket statement that “these cats aren’t adoptable.” I realize that is indeed true of many feral cats, even those who may seem tame in the presence of their caretakers. However, I worry that in some cases the assumption is made that the cats aren’t adoptable when that may not be the case.

Our neighborhood cats certainly seemed unadoptable when we first trapped them. It took a good deal of time and effort, following the advice of our local mentor, before we discovered that these cats were actually semi-domesticated and adoptable. I’m wondering if this isn’t another case of one overly simplistic talking point (i.e., “these cats should be put in homes instead of returned to the outdoors”) being countered by another overly simplistic talking point (i.e., “these cats aren’t adoptable”) instead of trusting new volunteers to understand a deeper level of complexity (i.e., whether cats can be adopted depends on many variables, such as availability of homes, resources for fostering the cats, how feral the cats have become, etc.). I’d be curious to know whether you think more can be done to encourage greater rates of adoption of trapped and sterilized cats prior to return to the outdoors.

PW: I suppose the message that “these cats aren’t adoptable” is intended not so much for the folks willing to put in the time (as you and your neighbors have done), but for the various stakeholders who so often misunderstand and/or misrepresent the fate of cats rounded up. It’s not uncommon for a shelter to have a live-release rate of 50 percent or less for cats. (Some, like Polk County (FL) Animal Control, kill more than 90 percent of cats brought in.) If the cats aren’t very adoptable from the moment they arrive, they’ll almost certainly be killed. And, when these cats are taking up precious cage space, it means more of the adoptable cats will be killed as well.

In my experience, it’s not so uncommon for colony cats to warm up to caregivers—charming their way into homes the way a couple of mine did. But it takes more time than most rescues/fosters would be willing to give. And unless they’re kittens, these cats don’t seem to do well indoors, anyhow. That said, there will certainly be exceptions. And I think adoption is a valuable aspect of TNR—better lives for the cats and some happy endings for their caretakers, too. And, fewer of them outdoors, of course.

•     •     •

When Walter first contacted me with his Q&A proposal, it was, he explained, with the “hope that we can set a better example of how to have a civil dialogue on this important topic than what you and I have encountered elsewhere.”

Indeed! Thank you, Walter, for the invitation.

* Full disclosure: I support Alley Cat Allies and Best Friends—financially (at a very modest level) and in terms of their overall missions—and I communicate with various individuals in both organizations on a regular basis. I’m also incredibly grateful for the support they’ve shown me (e.g., profiles in their publications, the opportunity to present at the recent No More Homeless Pets Conference, etc.).

American Bird Conservancy Calls for Killing of Cats

I don’t imagine USA Today has ever been accused of producing substantive journalism. And, judging from a worthless he-said/she-said-we-report-you-decide story in yesterday’s edition, that’s not likely to change anytime soon.

OK, not worthless, exactly. After all, American Bird Conservancy president George Fenwick finally went on record calling for the killing of free-roaming cats: “I detest the killing of cats and dogs or anything else. But this is out of control, and there may be no other answer.” [1]

How many cats are we talking about? Fenwick’s not saying. And reporter Chuck Raasch does readers no favors when he confuses free-roaming cats and feral cats (“Estimates of the U.S. feral cat population range from a few million to 125 million, with the Humane Society saying 50 million.”)

And in a move that’s become popular among TNR opponents,* Fenwick plays the “powerful cat lobby” card: “he worries his side is ‘out-emotioned’ and out-organized.” [1] It would, I think, be more accurate to say that “his side” has neither the science nor public opinion working in their favor. Read more

Kitty Cams and PR Scams

In a joint media release, the American Bird Conservancy and The Wildlife Society team up to misrepresent the results of a recent predation study, decrying the “ongoing slaughter of wildlife by outdoor cats.” Meanwhile the University of Georgia researcher contradicts her previous position that “cats aren’t as bad as biologists thought.”

“To be persuasive we must be believable; to be believable we must be credible; credible we must be truthful.”Edward R. Murrow

“‘KittyCam’ Reveals High Levels of Wildlife Being Killed by Outdoor Cats,” declares a media release issued today—a joint effort of the American Bird Conservancy and The Wildlife Society, and, to my knowledge, the first of its kind.

It’s difficult not to see this as an act of desperation—the PR-equivalent of an all-caps e-mail. I’m surprised it hasn’t happened sooner, though, given all that ABC and TWS have in common. Their shared disdain for TNR, obviously, but also their utter disregard for science, scientific literacy, and the truth about the impacts of free-roaming cats. Two peas in a pod, as it were. (Irony: peas are, alas, not native to North America.)

And so, their joint media release is exactly what one would expect: heavy on errors, misrepresentations, and glaring omissions, and light on defensible claims. Read more

Collisions, Predation, and Bird Populations

Masts of the Rugby Radio Station transmitter, Warwickshire, England. Courtesy of Wikimedia Commons and Sreejithk2000.

Recent research suggests that collisions with buildings and communication towers have no significant effect on bird populations. These findings raise additional questions about the often-implied connection between predation by free-roaming cats and declining bird numbers.

According to the American Bird Conservancy, 300 million to 1 billion birds are killed each year in “collisions with glass on buildings, from skyscrapers to homes.” As many as 50 million more are killed annually by communication towers.

Yet, according to a study published last September in the open-access, online publication PLoS ONE, “this conspicuous source of mortality has had no discernible effect on long-term population dynamics among North American landbirds.” [1]

“At worst,” suggest authors Todd Arnold and Robert Zink, conservation biologists from the University of Minnesota, “collision mortality could be described as an added burden for populations already in decline for other reasons.” [1]

Which would seem to be, if not good news for the folks at ABC, then at least news. (Even solutions “that can greatly reduce avian collision mortality at manmade structures,” warn the researchers, “will not halt population declines among North American migratory birds.” [1])

So, why is there no mention of this study—published nearly six months ago—on the ABC website?

I suspect it will never appear there—or in any ABC publication. And they’re certainly not going to mention it to the media—too many awkward questions about contradictory assertions, resource allocation, and the like. After all, this is an organization that prides itself on using “the best available science” to shape policy.

(To be clear: Arnold and Zink are not opposed to “the deployment of simple design solutions that can greatly reduce avian collision mortality at manmade structures,” [1] despite the rather dire results of their analysis.)

The Study
To better understand potential population-level impacts, Arnold and Zink compared “long-term records of avian mortality from communication towers and urban buildings… with population estimates and trend data from the North American Breeding Bird Survey.” [1] The relative vulnerability of various species (188 in the case of communication towers, 147 for buildings) was quantified by comparing the proportion of birds killed in collisions with towers and/or buildings with their proportion in the overall bird population.

Species with very high collision mortalities relative to their abundance were dubbed “super colliders,” while species with very low instances of collisions relative to their numbers were dubbed “super avoiders.”

The spread between the two extremes is astonishing. Bay-breasted warblers, for example, were found to be 236 times more likely to collide with towers than would be predicted by chance alone (but are nevertheless considered a species of Least Concern). Horned larks, on the other hand, are 688 times more likely to avoid the same towers.

Fascinating work! What caught my eye, though, was the authors’ suggestion that their analysis technique would be appropriate for assessing “many poorly quantified conservation threats [including] house cat predation.” [1]

Future (Hypothetical) Study
Curious, I contacted Arnold, asking him how one would go about conducting such a study. Surely, obtaining an accurate count of mortalities due to predation is far more complicated than tallying mortalities due to man-made structures (itself, no trivial undertaking).

In fact, the greatest challenge, suggests Arnold, is not the data collection or subsequent analysis.

“In order to do the scientific study that you asked about, it’s necessary to approach it objectively, and I’d worry that anybody tackling this issue would be in one camp or the other, and the study really demands an impartial referee. A possibly better alternative would be to get members of both sides to agree in a mediated discussion what would constitute a valid study of the issue, and how such a study would be designed, implemented, and interpreted.”

Fair enough. Still, though: if implementation and interpretation pose particular challenges, the design of the study is actually fairly straightforward. “To apply the approach that we used for tower and building collisions,” Arnold says, “you would need to assemble a large data set on what species of birds are killed by cats.”

“It would probably take a large network of citizen scientists to accumulate a database on species composition of cat-killed wildlife; they would need to be people who had frequent and regular access to one or more cats—so, cat owners, cat monitors, and cat stewards who would agree to participate on a long-term basis. It would be important that sampling wasn’t driven by spectacular events (e.g., a cat owner ignores several non-descript House Sparrows that their cat brings home, and only submits information when a colorful Northern Cardinal gets killed). Conversely, you’d need to worry about people who might report only the boring and common things and fail to report when a rare or well-loved bird is killed because they are ashamed or fear backlash from the bird-loving public.”

Proper identification of each species would, of course, be critical. This, says Arnold, could be done using digital photos or by collecting remains (a method often employed in predation studies [2] and [3] and [4]).

“The study would have to continue until several thousand birds had been identified to species (Bob Zink and I worked with data sets that were a minimum of about 5,000 dead birds). From the mortality records, one would first identify the species that were most vulnerable to cats by comparing their proportion in the cat-kill data to their expected proportion based on population estimates. So, say for example, that juncos and American robins were 5.2 and 3.2 percent of the mortality records, but only 1.3 and 1.6 percent of the total bird population, then they’d be 4 and 2 times more vulnerable to cats than expected by chance. Other species would be less vulnerable than expected by chance. This part of the study would identify which species of birds were most vulnerable to predation by cats, and a priori I’d expect to see that ground-feeding birds like juncos and robins were more vulnerable, as well as urban- and suburban-adapted birds like robins, starlings, chickadees, etc.”

As Arnold and Zink point out in their paper, “total body counts reveal little about relative mortality risk for each species”—a fact often overlooked or ignored by those trying to link predation by cats to declining bird populations. And so, “the final—but critical—step” in our hypothetical study, says Arnold, “is to ask: Does this mortality factor matter do bird populations?

“It obviously matters to the individuals that were killed, but given that 40–50 percent of the fall bird population is probably not going to be alive one year later, the focus here has to be on long-term population dynamics. And so, the final step would involve correlating the measure of vulnerability to cat predation from the first step with long-term population trends for these same species. If one finds that cat predation rates are not correlated with bird population trends, then it’s time to stop vilifying cats for bird declines (with the important caveat that it might still be important for one or two endangered/threatened species). If one finds that cat predation rates are negatively correlated with bird population declines, then it suggests that cats might be an important limiting factor of birds populations (with the important caveat that it might be due to some other unmeasured factor that is also correlated with cat predation).”

What We Already Know
Unfortunately, I’m in no position to undertake the study Arnold describes. And, in any case, am (unapologetically) in “one camp or the other.” (That said, I’d jump at the chance to be part of the aforementioned “mediated discussion.”)

On the other hand, there’s already plenty of research suggesting that predation does not necessarily result in population-level impacts. In The Domestic Cat: The Biology of Its Behaviour, for example, Mike Fitzgerald and Dennis Turner thoroughly reviewed 61 predation studies, concluding rather unambiguously: “We consider that we do not have enough information yet to attempt to estimate on average how many birds a cat kills each year. And there are few, if any studies apart from island ones that actually demonstrate that cats have reduced bird populations.” [5]

Also: it’s well-known that predators—cats included—tend to prey on the young, the old, the weak and unhealthy. Indeed, at least two research studies have investigated this phenomenon in great detail. In one, researchers comparing the fat reserves of birds killed by cats to those of birds killed through non-predatory events (e.g., collisions with windows or cars) found that “mean fat scores evident in the cat-killed birds… were sufficiently low that these individuals were likely to have had poor long-term survival prospects.” [6]

In another study, researchers found that songbirds killed by cats tend to have smaller spleens than those killed through non-predatory events, leading them to conclude that “avian prey often have a poor health status.” [7]

As the UK’s Royal Society for the Protection of Birds notes: “It is likely that most of the birds killed by cats would have died anyway from other causes before the next breeding season, so cats are unlikely to have a major impact on populations.” [8]

(Frank Gill makes this very point in the third edition of Ornithology: “With some conspicuous exceptions… predators don’t limit or regulate the bird populations on which they prey. Instead, they take weak, sick, and young birds, many of which are part of the surplus that exceeds locally limiting food supplies.” [9] When it comes to cats, however, Gill considers “managed feral cat colonies [to be] potentially a serious threat to local bird populations.”)

•     •     •

Granted, the studies referenced above are no substitute for the one Arnold describes. And I don’t expect ABC to “stop vilifying cats for declining bird populations” anytime soon.

Nevertheless, Arnold and Zink’s findings ought to make it more difficult for ABC (or any other organization blaming cats for declining bird populations) to continue using cats as scapegoats. After all, even using the figures cited by ABC, it seems quite likely that collisions with buildings and communication towers are responsible for more bird deaths than are cats.* And the man-made structures are taking out healthy individuals.

Of course, as Arnold notes in his e-mail, bird species vulnerable to man-made structures may not be vulnerable to predation by cats, and those vulnerable to predation by cats may not be vulnerable to collisions. Still, taken together, all of this research begs the question: If building- and tower-collisions aren’t having population-level impacts, how likely is it that free-roaming cats are?

Which is exactly what I asked Darin Schroeder, ABC’s Vice President of Conservation Advocacy, and Steve Holmer, their Director of the Bird Conservation Alliance. That was three weeks ago.

*According to The American Bird Conservancy’s Guide to Bird Conservation, “532 million birds [are] killed annually by outdoor cats.” [10] Though far less than the “one billion birds” sometimes cited by TNR opponents, [11] ABC’s “estimate” is based on some dubious assumptions.

Thanks to my friends at Alley Cat Allies for bringing Arnold and Zink’s paper to my attention.

Literature Cited
1. Arnold, T.W. and Zink, R.M., “Collision Mortality Has No Discernible Effect on Population Trends of North American Birds.” PLoS ONE. 2011. 6(9): p. e24708.

2. Churcher, P.B. and Lawton, J.H., “Predation by domestic cats in an English village.” Journal of Zoology. 1987. 212(3): p. 439-455.

3. Woods, M., McDonald, R.A., and Harris, S., “Predation of wildlife by domestic cats Felis catus in Great Britain.” Mammal Review. 2003. 33(2): p. 174-188.

4. Barratt, D.G., “Predation by House Cats, Felis catus (L.), in Canberra, Australia. I. Prey Composition and Preference.” Wildlife Research. 1997. 24(3): p. 263–277.

5. Fitzgerald, B.M. and Turner, D.C., Hunting Behaviour of domestic cats and their impact on prey populations, in The Domestic Cat: The biology of its behaviour, D.C. Turner and P.P.G. Bateson, Editors. 2000, Cambridge University Press: Cambridge, U.K.; New York. p. 151–175.

6. Baker, P.J., et al., “Cats about town: Is predation by free-ranging pet cats Felis catus likely to affect urban bird populations? Ibis. 2008. 150: p. 86–99.

7. Møller, A.P. and Erritzøe, J., “Predation against birds with low immunocompetence.” Oecologia. 2000. 122(4): p. 500–504.

8.  n.a. (2011) Are cats causing bird declines? Accessed October 26, 2011.

9. Gill, F.B., Ornithology. 3rd ed. 2007, New York: W.H. Freeman. xxvi, 758 p.

10. Lebbin, D.J., Parr, M.J., and Fenwick, G.H., The American Bird Conservancy Guide to Bird Conservation. 2010, London: University of Chicago Press.

11. Dauphine, N. and Cooper, R.J., Impacts of Free-ranging Domestic Cats (Felis catus) on birds in the United States: A review of recent research with conservation and management recommendations, in Fourth International Partners in Flight Conference: Tundra to Tropics. 2009. p. 205–219.

12 Sparrows Stressing

Song Sparrow, Whitby, Ontario. Photo courtesy Wikimedia Commons and Mdf.

New study attempts to demonstrate how the presence of predators alone can reduce songbird reproduction by bombarding birds with round-the-clock audio recordings of predator noises. One co-author of the study goes further, attempting to implicate cats.

The purpose of scientific inquiry (am I wrong about this?) is to reveal some truth about our world. Or the universe, in the case of astrophysics, say. Or, if we want to zoom out (and in, simultaneously) further still, the multiverse. Regardless of the particular phenomena under investigation, it’s essential that the methods employed replicate—to the extent possible—real-world conditions as closely as possible.

Easier said than done—especially when the work is set in the messy, often uncooperative, real world, where researchers struggle to balance the desire for laboratory-like control (necessary for valid analysis) with the vérité-like need for authenticity (necessary for valid conclusions). Or not, as a study published last week in Science demonstrates.

According to a story on the publication’s website, the research “shows that the mere sound of predators reduces both the number and survival rate of songbird offspring, regardless of the true threat.”

In fact, the songbirds in question were subject—Waco- or Guantánamo-style—to a round-the-clock barrage of menacing sounds over the entire four-month breeding season. Little wonder, then, their productivity was affected; what’s surprising is that these birds and their offspring survived at all (and didn’t decamp to quieter—even inviting (more on that shortly) terrain nearby).

What’s this got to do with cats? As Michael Clinchy, Adjunct Assistant Professor in the University of Victoria’s Department of Biology, and co-author of the study, explains in the ScienceNOW story, “our results show that the mere presence of this introduced predator is enough to negatively impact native wildlife.”

Perhaps Clinchy was expecting readers to overlook the bizarre methods he and his colleagues used. Or read their paper, “Perceived Predation Risk Reduces the Number of Offspring Songbirds Produce per Year” (PDF), in which there is no mention of cats at all.

But for those of us who are paying attention, it’s clear: Clinchy is simply in no position to comment on the possible impact of cats—or, for that matter, any predator that doesn’t routinely participate, together with a host of other predators, both avian and mammalian, in a maniacal chorus incessantly tormenting the song sparrows breeding on British Columbia’s Gulf Islands (culminating, by the way, in no physical attack—which, no doubt, only further unsettles and disorients the targeted birds).

The Study
Joining Clinchy in the research was frequent collaborator Liana Zanette, Associate Professor in the University of Western Ontario’s Department of Biology (lead author of the paper), along with Aija F. White and Marek C. Allen, both of UWO. The objective, they explain, “was to test whether perceived predation risk per se affected offspring production.” [1]

To do so, the researchers exposed song sparrows on five of BC’s Gulf Islands to “playlists” of various “calls and sounds” either of predators known to frequent the area, or of the area’s non-predators. Among the predators were the common raven, northwestern crow, Cooper’s hawk, brown-headed cowbird, raccoon, and three species of owls. (The closest we get to a cat is a “brush disturbance sound.”) Non-predators included the Canada goose, mallard duck, northern flicker, Rufous hummingbird, belted kingfisher, downy woodpecker, common loon, harbor seal, and two species of frog (along with “surf sound,” a benign match to the aforementioned brush disturbance sound).

“To compose our playlist of non-predator calls and sounds,” write Zanette et al., “we:

“(i) excluded any associated with either obvious competitors (other songbirds), or potential food sources (invertebrates, e.g. crickets chirping); (ii) included only calls and sounds known to be heard at our study locations; (iii) matched our diurnal predator list with a diurnal non-predator list, and our nocturnal predator list with a nocturnal non-predator list; and then (iv) matched each predator with a non-predator call or sound that had acoustic properties that were as similar as possible.” [1]

Twelve nesting females were exposed to the predator playlist; while 12 others, located nearby, were exposed to the non-predator playlist. “Playbacks were broadcast every few minutes, 24 hours per day on a 4-day-on-4-day-off cycle, throughout the 130-day breeding season.” [2] (Average daytime interval: 2 minutes 20 seconds of playback followed by 3 minutes 30 seconds of silence; average nighttime interval: 2 minutes 20 seconds/5 minutes 22 seconds. [1])

Nest predation was prevented by “protecting every nest in the experiment with both electric fencing and seine netting.” [2]

To evaluate the effect of the predator playback broadcasts, the researchers compared several metrics between the two groups of sparrows. Among them:

“the number of offspring produced per year… egg and brood mass, nestling susceptibility to thermoregulatory stress (skin temperature 10 min after mother flushed from nest), and four measures of behavior reflective of effects on habitat use: nest site selection, vigilance (flight initiation distance, i.e., distance of experimenter from nest when mother flushed from nest), nest attendance (incubation bout duration), and foraging (parental feeding visits per hour during brood-rearing).” [2]

(Note: A detailed description of the methods and analysis employed, as well as photos of the site and equipment used, can be found in the paper’s “Supporting Online Material” (PDF))

The data show that predator-playback females produced, on average, few eggs, nestlings, and fledglings than their non-predator-playback counterparts, for a 40 percent reduction in offspring overall. In addition:

“predator-playback females built their nests in denser, thornier vegetation, were more skittish… and spent shorter times on and longer times off the nest during incubation, and predator-playback parents made fewer feeding visits per hour during brood-rearing. Effects on all four behaviors were associated with effects on offspring number and condition.” [2]

The Researchers
Zanette and Clinchy have been studying the Gulf Island’s song sparrows for 12 years or more now, their work focused largely on the demographic impacts of predatory pressures and food supply (as well as the interaction of the two: “We conclude that annual reproductive success in song sparrows is a function of both food-restricted production and predator-induced loss and indirect food and predator effects on both clutch and brood loss.” [3]). Predation by cats plays only a minor role in their published work, yet both Zanette and Clinchy seem quite eager to talk up that role for more mainstream audiences.

In an interview on CBC’s The Current about her participation in the documentary Cat Crazed, for example, Zanette describes research in which she and Clinchy used video cameras to “capture predators in the act of preying upon songbird nests” in Rithet’s Bog, 10–15 miles south the Gulf Islands.

“What we’ve found over the years is that, of all predation events that we recorded, cats are responsible for 22 percent of those. OK, so that’s cats going in and taking songbird eggs, and chewing on songbird nestlings—completely wiping out the reproductive effort of those parent birds… They chomp, and sometimes they look at the camera and they lick their lips afterwards.”

Although Zanette does acknowledge some other culprits—rats and brown-headed cowbirds, mostly—it’s with far less enthusiasm. Granted, the interview wasn’t about rats or cowbirds, but the context doesn’t explain the outsized impact Zanette ascribes the bog’s cats.

Clinchy’s also interviewed for the film—which, I need to point out, I’ve yet to see, as it’s unavailable for online streaming outside of Canada (and, for reasons that will become clear momentarily, I refuse to purchase the DVD). However, in a story appearing in the online version of Vancouver’s Georgia Straight, which the publication describes as “Canada’s largest urban weekly,” Judith Webster (author of the highly recommended 2007 paper “Missing Cats, Stray Coyotes: One Citizen’s Perspective”) notes: “it’s clear Clinchy was directed by the Cat Crazed interviewer to focus on his lack of fondness for cats.”

And then there’s his comment last week about “this introduced predator.” All in all, it’s difficult to take these two seriously when they start talking about the impact of cats on the song sparrows they study.

(None of which explains, however, why I haven’t bought the Cat Crazed DVD. That’s because of my dislike for the film’s director, Maureen Palmer, who, in addition to the obvious bias she brought to Cat Crazed, apparently lied to the Toronto Star about the conditions of the cats treated by FixNation, a top-notch high-volume spay-neuter clinic north of Los Angeles. I’d hate to see even a dime of my money—10.2 cents Canadian—used to support her agenda.)

The Sparrows
“Our results suggest that the perception of predation risk is itself powerful enough to affect wildlife population dynamics,” write Zanette et al., “and should thus be given greater consideration in vertebrate conservation and management.” [2] Even setting aside for the moment the unrealistic methods employed, the fact that these sparrows produced 40 percent fewer offspring doesn’t necessarily demonstrate population-level impacts; a single breeding season’s observations are hardly sufficient to make such projections.

And, more to the point, the authors don’t actually mention anything about the population dynamics of song sparrows in the real world. The Song Sparrow is, according to the Cornell Lab of Ornithology website, a species of Least Concern. That said, Breeding Bird Survey data indicate a 0.6 percent annual decrease, on average, from 1966 through 2009. (Among the most credible BBS data, the steepest decline, 2.1 percent, was seen in Alberta, while the greatest annual increase, 5.0 percent, comes from Missouri.)

So, is the decline suggested by BBS data the result of song sparrows subject to the “calls and sounds” of cats (or any number of “brush disturbance sounds”)? I suspect it has much more to do with the calls and sounds of humans—whose numbers in the U.S. soared 55 percent, from 197 to 307 million, between 1966 and 2009.

In fact, the interaction of cats and song sparrows has been studied in some detail when Cole Hawkins conducted his PhD work during the mid-1990s in two Alameda County, CA, parks. As I’ve mentioned previously, Hawkins’ conclusions are largely indefensible, but I take him at his word when it comes to his bird counts. And song sparrows were among five (of nine total) ground-feeding species that demonstrated “no clear preference for the no-cat or cat area [where up to 26 cats were being fed regularly].” [4] (In fact, in nine of the 14 surveys conducted over the course of Hawkins’ research, the number of song sparrows seen in the cat area exceeded the number seen in the no-cat area—in some cases by a factor of two or three.)

Yet, for all Zanette and Clinchy’s apparent concern for cats predating song sparrows, they never once cite Hawkins’ work.

The Take-away
I’ve no doubt that this study was, as the researchers themselves describe it, “logistically very challenging.” [1] Managing the technology involved (which doesn’t always cooperate in the field) and the constant monitoring of nests and nestlings would, alone, keep a team of bright, ambitious researchers on their toes. But hard work, in and of itself, does not necessarily produce meaningful results.

As Julie Levy, Maddie’s Professor of Shelter Medicine in the University of Florida’s College of Veterinary Medicine, mentioned in a comment on the ScienceNOW website, the study would have benefited from a “baseline control group” not subjected to the same “high degree of investigator interference.”

Levy goes on to speculate (admitting “it may be far-fetched”) that the non-predator-playback sparrows may have been “so relaxed and comfortable that their fledgling rate increased by 40 percent.”

Maybe it’s not so far-fetched.

Australian National University biologists Tonya Haff and Robert Magrath, whose work is cited by Zanette et al., argue that nestlings are “finely tuned to their acoustic world, and responded appropriately to sounds of danger nearby.” [5] So why couldn’t adult birds pick up on cues—broadcast continuously every 96 hours—suggesting that (1) there is no danger, and (2) food supplies are plentiful?

The predator-playback group, by contrast, would be picking up cues unlike anything they’d ever experienced: round-the-clock danger, in the air and on the ground.

One wonders, too, what impact a single-predator playback—say, Cooper’s hawks—might have had, used in intervals that mimic real-world conditions. Although Zanette et al. “have yet to observe them attacking a nest, they have been recorded doing so elsewhere and are known to represent a significant threat to adult sparrows.” [1] And, as Zanette and Clinchy point out in a previous paper, their research site has “the highest density of Cooper’s hawks in Canada.” [6]

In fact, Zanette et al. have already set the stage for such investigations—and funding: “it will be fruitful to evaluate the effects of cues from specific predators in future studies.” [1]

The Reaction
Not surprisingly, “Perceived Predation Risk” made UWO’s homepage, the proud university overstating the (already-overstated) implications of the work (even the authors must wince at the word prove): “New findings from Western prove fear of predation risk is powerful enough to affect wildlife populations even when predators are prevented from directly killing any prey.”

And it took The Wildlife Society’s Michael Hutchins less than 24 hours to endorse the paper, calling it “devastating to feral cat TNR advocates.” Misquoting Clinchy, Hutchins goes on to say the paper “is just another example of the growing peer-reviewed literature on this topic, which are providing strong evidence for the negative impact of feral cats on our native wildlife.” Demonstrating once again (as if we needed any more evidence) his commitment not to sound science, but to any headline that might drum up support for his witch-hunt (and year-end donations). (My comment, by the way, is awaiting approval.)

•     •     •

In the end, I’m left to wonder how studies such as this one—with its deeply flawed design—receive funding in the first place (in this case, by the Natural Sciences and Engineering Research Council of Canada and the Canada Foundation for Innovation and the Natural Sciences) and then warrant publication in Science (“the world’s leading outlet for scientific news, commentary, and cutting-edge research”).

Instead of increasing our understanding of the world, this research only adds to our misunderstanding.

I attempted to contact both Zanette and Clinchy by e-mail on Friday, but have yet to receive a reply (though there have been multiple visits to the Vox Felina site from in and around London, Ontario, where Zanette is based). Zanette never replied to my previous inquiry, either, related to her comments in the CBC interview.

Literature Cited
1. Zanette, L.Y., et al., “Perceived Predation Risk Reduces the Number of Offspring Songbirds Produce per Year (Supporting Online Material).” Science. 2011. 334(1398).

2. Zanette, L.Y., et al., “Perceived Predation Risk Reduces the Number of Offspring Songbirds Produce per Year.” Science. 2011. 334(6061): p. 1398–1401.

3. Zanette, L., Clinchy, M., and Smith, J.N.M., “Combined food and predator effects on songbird nest survival and annual reproductive success: results from a bi-factorial experiment.” Oecologia. 2006. 147: p. 632–640.

4. Hawkins, C.C., Impact of a subsidized exotic predator on native biota: Effect of house cats (Felis catus) on California birds and rodents. 1998, Texas A&M University.

5. Haff, T.M. and Magrath, R.D., “Vulnerable but not helpless: Nestlings are fine-tuned to cues of approaching danger.” Animal Behaviour. 2010. 79(2): p. 487–496.

6. Zanette, L., et al., “Synergistic effects of food and predators on annual reproductive success in song sparrows.” Proceedings of The Royal Society B. 2003. 270: p. 799–803.

Devolution In the Classroom: Three Editions of F. Gill’s “Ornithology”

For more than 20 years now, Gill’s classic text has been required reading for ornithology students. While the book’s attention to conservation issues has expanded over its three editions, its treatment of the impact of cats on bird populations reflects an unsettling shift away from science.

The hoards of students descending upon college campuses this fall will—despite the rise of the eco-friendly PDF and a great variety of online content—more often than not find their arms and backpacks stuffed with old-school printed-and-bound books. Among them will be Frank Gill’s Ornithology, a regular offering on campus bookstore shelves for 21 years now.

Gill’s Ornithology is, I’m told by one Vox Felina reader, “considered (at least in these parts) the text regarding ornithology.” From what I can tell, it’s popularity as required reading for third- and fourth-year undergraduates isn’t limited to any one region of the country. Indeed, according to, the book is “the classic text for the undergraduate ornithology course.” Its third edition, published in 2007, “maintains the scope and expertise that made the book so popular while incorporating a tremendous amount of new research.”

Unfortunately, none of this new research made it into the section—a single paragraph—meant to address the “threat” of cats. Indeed, students interested in this topic are better off with the first edition, published 17 years earlier.

First Edition
“The numbers of deaths attributable directly or indirectly to human actions each year during the 1970s are staggering,” writes Gill in the 1990 edition of Ornithology, “but are apparently minor in relation to the population level.” [1] Citing a 1979 U.S. Fish and Wildlife Service report by Richard C. Banks, Gill continues:

“Human activities are responsible for roughly 270 million bird deaths every year in the continental United States. This seemingly huge number is less than two percent of the 10 to 20 billion birds that inhabit the continental United States and appears to have no serious effect on the viability of any of the populations themselves, unlike human destruction of breeding habitat and interference with reproduction… Miscellaneous accidents such as impact with golf balls, electrocution by transmission lines, and cat predation, may amount to 3.5 million deaths a year.” [1]

Predation by cats (included under “All Other Indirect”), then, according to Banks, represents about 1.3 percent of overall human-caused mortality—a loss of, at most, 0.04 percent of the U.S. bird population annually. By contrast, hunting and “collision with man-made objects” combine to make up “about 90 percent of the avian mortality documented” in Banks’ report. [2]

Second Edition
Five years later, in the second edition, the story changes dramatically. Gill discards Banks’ reference to cats and uses his 270 million figure purely for dramatic effect—the set-up for a punch line in the form of Rich Stallcup’s back-of-the-envelope guesswork (which Stallcup himself considered “probably a low estimate” [3]). Gill even includes a bar chart to drive the point home. (Apparently, he didn’t find Banks’ pie chart compelling enough to include in the his first edition of Ornithology.)

“Human activities are directly responsible for roughly 270 million bird deaths every year in the continental United States, about 2 percent of the 10 to 20 billion birds that inhabit the continental United States (Banks 1979)… Dwarfing these losses are those attributable to predation by pets. Domesticated cats in North America may kill 4 million songbirds every day, or perhaps over a billion birds each year (Stallcup 1991). Millions of hungrier, feral (wild) cats add to this toll, which is not included in the estimate of 270 million bird deaths each year.” [4]

But Stallcup’s “estimate”—published in the Observer, a publication of the Point Reyes Bird Observatory (which Stallcup co-founded)—lacks even the slightest scientific justification. In fact, “A Reversible Catastrophe” is little more than Stallcup’s advice—at once both folksy and sinister—about defending one’s garden from neighborhood cats (“…try a B-B or pellet gun. There is no need to kill or shoot toward the head, but a good sting on the rump seems memorable for most felines, and they seldom return for a third experience.” [3]).

“Let’s do a quick calculation, starting with numbers of pet cats. Population estimates of domestic house cats in the contiguous United States vary somewhat, but most agree the figure is between 50 and 60 million. On 3 March 1990, the San Francisco Chronicle gave the number as 57.9 million, ‘up 19 percent since 1984.’ For this assessment, let’s use 55 million.

“Some of these (maybe 10 percent) never go outside, and maybe another 10 percent are too old or too slow to catch anything. That leaves 44 million domestic cats hunting in gardens, marshes, fields, thickets, empty lots, and forests.

“It is impossible to know how many of those actively hunting animals catch how many birds, but the numbers are high. To be very conservative, say that only one in ten of those cats kills only one bird a day. This would yield a daily toll of 4.4 million songbirds!! Shocking, but true—and probably a low estimate (e.g., many cats get multiple birds a day).” [3]

It’s hardly surprising that Stallcup’s “estimate” grossly exaggerates predation rates since his research never went any further than the Chronicle’s mention of the U.S. pet cat population. His assumptions about how many of these cats go outdoors and their success as hunters stand in stark contrast to the trend suggested by pet owner survey results and various predation studies (some of which suggest that just 36–56 per­cent of cats are hunters. [5, 6])

(It was, no doubt, the “shocking” aspect of Stallcup’s numbers that appealed to Nico Dauphine, who, in her “Apocalypse Meow” presentation, acknowledges that Stallcup “didn’t do a study” but nevertheless concludes, inexplicably, that his “is a conservative estimate.”)

Unnatural Selection
So, how did Stallcup’s indefensible “estimate” make it into the standard ornithology textbook? It was, Gill told me recently by e-mail, “one of the few refs [he] could find.”

Referring to what he calls “the great cat debates,” Gill writes: “I claim no great expertise or authority… now or in the ancient histories of early textbook editions.”

Fair enough. Writing, editing, and revising multiple editions of Ornithology was an enormous undertaking—one for which Gill deserves much credit. But there was, available at the time, work by scientists who, unlike Stallcup actually studied predation. Indeed, even before the first edition of Ornithology was published, a great deal of work had been done—and compiled in the first edition (published in 1988) of The Domestic Cat: The Biology of Its Behaviour. In it, Mike Fitzgerald, one of the world’s foremost experts on the subject, reviewed 61 predation studies, concluding:

“Predation on songbirds by domestic cats is noticed because it takes place during the day, whereas much predation on mammals takes place at night. People generally enjoy having songbirds in their gardens, and providing food in winter may increase the numbers of birds. When cats kill some of these birds, people assume that cats are reducing the bird populations. However, although this predation is so visible, and unpopular, remarkably little attempt has been made to assess its impact on populations of songbirds.” [7]

Two years later, Fitzgerald had a brief letter on the subject published in Environmental Conservation. His comments are as relevant today as they were some 21 years ago:

“Before embarking… on programmes to educate the public so that they will pressure elected officials to act on ‘cat delinquency,’ we must discover what effect domestic cats really have on the wildlife populations in various urban localities—not merely what effect we assume they have on the basis of prey brought home by cats in one English village. Although we know what prey cats bring home in a few urban localities, we do not know what effect this predation has on the prey populations, or how the wildlife populations might differ if cat populations were reduced. Until we have this information we cannot ensure sound educational programmes. We should perhaps also try to discover what values urban people place on their wildlife and their pets—it seems likely that many of the people who love their pets also treasure the wildlife.” [8]

Surely, Fitzgerald’s work would have been more appropriate for, and useful to, Ornithology’s audience. Instead, unsuspecting undergraduates were treated to biased editorializing dressed up as science.

Third Edition
Gill tells me I wasn’t the first to “react… to the Stallcup paper,” and that the push-back was sufficient to prompt its removal from the third edition. Gone, too, is Banks’ report. Instead, Gill employs the now-common kitchen-sink approach, rattling off a litany of sins—borrowed, it seems, from the American Bird Conservancy.

“Domestic house cats in North America, for example, may kill hundreds of millions of songbirds each year. Farmland and barnyard cats kill roughly 39 million birds (and lots of mice, too) each year. Millions of hungrier, feral (wild) cats add to this toll. There is a common-sense solution. Letting cats roam outside the house shortens their expected life span from 12.5 years to 2.5 years and increases their risk of rabies, distemper, toxoplasmosis, and parasites. Evidence is mounting that cats help to spread diseases such as Asian bird flu. The message is clear: Keep pet cats inside for their own well being and for the future of backyard birds (” [9]

That 39 million birds figure, of course, comes from the infamous “Wisconsin Study,” the authors of which claim: “The most reasonable estimates indicate that 39 million birds are killed in the state each year.” [10] (The “reason” is, in fact, notably absent from Coleman and Temple’s figure—which can be traced to “a single free-ranging Siamese cat” that frequented a rural residential property in New Kent County, Virginia. [11])

Its implied use as a nationwide estimate, Gill says, was “a lapse.” The more serious lapse by far, though—not in copyediting but in judgment—is Gill’s endorsement of ABC.

A Constructive Approach
While he readily admits that he’s “not tracked nor verified [ABC’s] stats (and have paid precious little attention to the issue for almost 10 years),” Gill’s support is unwavering.

“ABC has taken a lead role on the cat-bird issues, generally with a constructive approach, which I applaud, given how polarized the debates can be.”

Constructive? As I’ve pointed out repeatedly, no organization has been more effective at working the anti-TNR pseudoscience into a message neatly packaged for the mainstream media, and eventual consumption by the general public. (The Wildlife Society, though, which shares ABC’s penchant for bumper-sticker science and public discourse via sound-bites, is at least as eager to participate in the witch-hunt.)

Among the more glaring examples: senior policy advisor, Steve Holmer’s claim, quoted in the Los Angeles Times, that “there are about… 160 million feral cats [nationwide]” [12]; ABC’s promotion of “Feral Cats and Their Management,” with its absurd $17B economic impact “estimate,” published last year by the University of Nebraska-Lincoln; and the numerous errors, exaggerations, and misrepresentations that persist in their brochure Domestic Cat Predation On Birds and Other Wildlife (PDF)—including a rather significant blunder that Ellen Perry Berkeley brought to light seven years ago in her book TNR Past, Present and Future. [13]

A constructive approach begins, by necessity, with sound science. But when it comes to the issue of free-roaming cats, at least, ABC has demonstrated neither an interest nor an aptitude.

So how does such an organization end up as the sole resource listed in a widely-used undergraduate textbook? (One written by the same man who served as the National Audubon Society’s chief scientist from 1996 to 2005, no less.) What’s next—physiology and nutrition books directing students to the PepsiCo Website for their hydration lesson? Psychology texts deferring to Pfizer (makers of Zoloft) on selective serotonin reuptake inhibitors?

Frank Gill’s View
Gill never responded to my follow-up questions for this post. Still, his comments during our first exchange shed some light on his general attitude toward cats. “I have owned some wonderful (Siamese) cats in my life,” Gill explained, “so I do view them positively in many ways. But when they are dumped near a research station by returning vacationers and then eat the ringed birds I have been studying for many years, I take a different view.”

He followed this last sentence with a smiley-face emoticon, though the joke was clearly wasted on me.

“My informal view now is that managed feral cat colonies are potentially a serious threat to local bird populations, including both migrants that stopover in urban parks and endangered shorebird colonies. Sustaining those colonies should be prohibited generally. The return of coyotes to suburban landscapes is most welcome both to add a top predator to these ecosystems and to counter the numbers of feral cats as well as other midsized predators that impact breeding productivity. Just their presence in a neighborhood should persuade cat owners to keep their cats safely inside!”

•     •     •

It would be a mistake to suggest that the sloppy, flawed research I spend so much time critiquing can be traced directly to the second or third editions of Frank Gill’s textbook. Still, for many students, the path to a degree in ornithology (and onto related graduate degrees) leads through the book of the same name. As such, Ornithology may well be their first exposure to issues of population dynamics, conservation, and the like.

First impressions tend to be lasting ones. If, as a wide-eyed undergraduate, you “learned” that cats kill up to four million songbirds every day, how might that shape your future studies? Your career? What if you “learned” that such predation takes a $17B toll on the country annually?

Considering the tremendous burden we’re placing on future generations, why would we hobble them—before they even get started, really—with such misinformation and bias? They’ve got more than enough on their plate without having to fact-check their textbooks, too.

Literature Cited
1. Gill, F.B., Ornithology. 1st ed. 1990, New York: W.H. Freeman and Company. 660.

2. Banks, R.C., Special Scientific Report—Wildlife No. 215. 1979, United States Department of the Interior, Fish and Wildlife Service: Washington, DC. p. 16.

3. Stallcup, R., “A reversible catastrophe.” Observer 91. 1991(Spring/Summer): p. 8–9.

4. Gill, F.B., Ornithology. 2nd ed. 1995, New York: W.H. Freeman and Company.

5. Perry, G. Cats—perceptions and misconceptions: Two recent studies about cats and how people see them. in Urban Animal Management Conference. 1999.

6. Millwood, J. and Heaton, T. The metropolitan domestic cat. in Urban Animal Management Conference. 1994.

7. Fitzgerald, B.M., Diet of domestic cats and their impact on prey populations, in The Domestic cat: The biology of its behaviour, D.C. Turner and P.P.G. Bateson, Editors. 1988, Cambridge University Press: Cambridge; New York. p. 123–147.

8. Fitzgerald, B.M., “Is Cat Control Needed to Protect Urban Wildlife? Environmental Conservation. 1990. 17(02): p. 168-169.

9. Gill, F.B., Ornithology. 3rd ed. 2007, New York: W.H. Freeman. xxvi, 758 p.

10. Coleman, J.S., Temple, S.A., and Craven, S.R., “Cats and Wildlife: A Conservation Dilemma.” 1997.

11. Mitchell, J.C. and Beck, R.A., “Free-Ranging Domestic Cat Predation on Native Vertebrates in Rural and Urban Virginia.” Virginia Journal of Science. 1992. 43(1B): p. 197–207.

12. Yoshino, K. (2010, January 17). A catfight over neutering program. Los Angeles Times, from,0,1225635.story

13. Berkeley, E.P., TNR Past present and future: A history of the trap-neuter-return movement. 2004, Bethesda, MD: Alley Cat Allies.

Fantasy Islands

Thirty-three: that’s how many species of birds have been driven to extinction by feral cats. At least.

I’ve lost track of how many times I’ve stumbled across references to this figure over the past couple years. Not once, however, have I seen more than one species (usually the Stephens Island Wren, its story having been twisted into mythology over the years) mentioned as an example.

Which species? From where? Under what circumstances?

I seemed to be the only one interested in these questions. Indeed—as is often the case with such “facts”—the impact of the 33 extinctions reference increases the further it’s separated from its original context.

Recent Sightings
The most recent reference comes from Kiera Butler’s article in the July/August issue of Mother Jones. Domestic cats, Butler writes, are “responsible for at least 33 avian extinctions worldwide.” [1]

The authors of Feral Cats and Their Management, published last year by the University of Nebraska-Lincoln, qualified the role of cats somewhat: “While loss of habitat is the primary cause of species extinctions, cats are responsible for the extinction of at least 33 species of birds around the world.” [2]

Nico Dauphine mentioned the 33 extinctions in her now-infamous “Apocalypse Meow” presentation, and in her 2009 Partners In Flight paper, co-written with Robert Cooper: “Historically, cats have been specifically implicated in at least 33 bird extinctions, making them one of the most important causes of bird extinctions worldwide (Nogales et al. 2004).” [3]

In “A Review of Feral Cat Eradication on Islands,” Nogales et al. explain: “Feral cats are responsible for the extinction of at least 33 bird species. Insular endemic landbirds are most frequently driven to extinction.” [4, emphasis mine]

So we’re talking about islands? That’s no small distinction, as Fitzgerald and Turner make clear in their contribution to The Domestic Cat: The biology of its behaviour:

“Cats have become established within the last century or two on many oceanic islands that, by the nature of their origin, had very few if any mammals but possessed avian faunas that had evolved without mammalian predators. In these circumstances, cats have had severe effects, that were often combined with the effects of other introduced mammals and habitat modification.” [5]

In Search Of 33 Extinctions
As their source, Nogales et al. cite a 1994 book by Christopher Lever, Naturalized animals: The ecology of successfully introduced species, which in turn points us to a 1977 text:

“According to Jackson (1977), naturalized predators have collectively been responsible for the extermination throughout the world of no fewer than 61 avian taxa, the principal culprits being feral domestic Cats which have caused 33 extinctions, rats 14, and the Small Indian Mongoose nine. These are in addition to the numerous occasions of local extinctions.” [6]

Now we’re getting somewhere. Jackson provides a bar chart illustrating the “Relative importance of causes of avian extinctions since 1600; data are summarized from Ziswiler (1967).” [7]

Now, a truly thorough search wouldn’t end with Ziswiler’s work—as he cites four additional sources. Nevertheless, Ziswiler provides what I was looking for: the various species that were driven to extinction, their location, and an approximate date.

And—just as important—the various other factors that acted in combination with predation by cats (which Ziswiler lists in what appears to be hierarchical order, though it’s not entirely clear).

That’s right: not only are these extinctions limited to island habitats, they typically involve two or three contributing factors. In fact, of the 33 extinctions tabulated by Ziswiler, only eight are attributed to cats exclusively (and it turns out some of those have been “overturned” in the 44 years since Ziswiler first published his list, as we’ll see shortly).

All of which is pretty difficult to reconcile with, say, Butler’s straightforward indictment: cats are “responsible for at least 33 avian extinctions worldwide.” [1]

Cats and Avian Extinctions
Of the eight extinctions Ziswiler attributes to cats alone, just two have stood the test of time: the Stephens Island Wren and the Macquarie Island kakariki (red-crowned parakeet), as described below.

  • Stephens Island Wren (Xenicus lyalli; Traversia lyalli)
    Location: Stephens Island
    Cause (Ziswiler): feral cats
    What we know now: “Traversia lyalli is only known from recent times from Stephen’s Island, New Zealand, although it is common in fossil deposits from both of the main islands. It is not thought to have existed beyond 1894… Construction of a lighthouse on Stephens Island in 1894 led to the clearance of most of the island’s forest, with predation by the lighthouse keeper’s cat delivering the species’ coup-de-grace.” (BirdLife International)

    In fact, the story of the “lighthouse keeper’s cat” is only partly accurate.

    Drawing upon “archival and museum records,” Galbreath and Brown found that, contrary to popular accounts, it was not a single cat, but “a small population of cats… preying on the birds and other life of the island.” [8]

    “They had a considerable impact on the land birds of the island: the flightless Traversia lyalli was only the first to disappear. Judging by the numbers of specimens obtained in 1894 and subsequent years, the species was reduced considerably in that first year and eliminated entirely within perhaps a few more years. Extermination was rapid, although probably not as rapid as usually stated, nor by a single cat. But although the extinction of the Stephens Island wren may not have been quite as dramatic as it has usually been portrayed, it was tragic enough. Traversia lyalli was only one of the casualties of human exploitation of Stephens Island, which could, with just a little more care, have remained a safe haven for this and other species now entirely extinct.” [8]

  • Macquarie Island kakariki (Cyanoramphus novaezelandiae erythrotis)
    Location: Macquarie Island
    Cause (Ziswiler): feral cats
    What we know now: “For 70 years following the discovery of Macquarie Island in 1810 the endemic parakeet Cyanoramphus novaezelandiae erythrotis remained plentiful, despite the introduction of cats (Felis catus) and other predators. The crucial factor in the bird’s rapid disappearance between 1881 and 1890 appears to have been the successful liberation of rabbits (Oryctolagus cuniculus) in 1879. This led to great increases of feral cats and introduced wekas (Gallirallus australis) and presumably to greatly intensified predation on parakeets.” [9]

    Macquarie Island provides an interesting footnote: A 15-year cat eradication effort on the island, a United Nations Educational, Scientific and Cultural Organization World Heritage Site, concluded in 2000 with “unintended consequences [that] have been dire.” In the absence of cats, the population of rabbits and rodents has skyrocketed, prompting the Australian government to commit AU$24 million to further eradication efforts. [10]

Other Factors
Three of the other six cat-caused extinctions described by Ziswiler actually involve a host of factors, as revealed by 44 years of additional research

  • Guadalupe storm petrel (Oceanodroma macrodactyla)
    Location: Guadalupe
    Cause (Ziswiler): feral cats
    What we know now: “The main cause of its demise is thought to be heavy predation by feral cats, compounded by goats destroying and degrading nesting habitat.” However, “it cannot yet be presumed to be Extinct because there have been no thorough surveys of this difficult-to-detect species in the appropriate season since 1906, and relatively recent reports of unidentified storm-petrels calling at night, plus the persistence of Leach’s Storm-petrel breeding on the island provide some hope that it may survive. Any remaining population is likely to be tiny, and for these reasons it is treated as Critically Endangered (Possibly Extinct).” (BirdLife International)
  • Choiseul crested pigeon (Microgoura meeki)
    Location: Choiseul Island
    Cause (Ziswiler): feral cats
    What we know now: “Its extinction was presumably caused by predation by feral dogs and cats, as suitable habitat survives on the island… It has not been recorded since 1904 despite searching and interviews with villagers.” (BirdLife International)
  • Bonin crested pigeon (Comumba versicolor)
    Location: Bonin Islands
    Cause (Ziswiler): feral cats
    What we know now: “Its extinction presumably resulted from clearance of the islands’ subtropical evergreen forest, and from predation by introduced cats and rats… It was last recorded in 1889.” (BirdLife International)

Natural Disaster
The case of the St. Christopher Bullfinch is intriguing in that cats may not have been involved at all.

  • St. Christopher Bullfinch (Loxigilla portoricensis grandis)
    Location: St. Christopher Island
    Cause (Ziswiler): feral cats
    What we know now: In 1979, Herbert Raffaele offered an explanation that makes no mention of cats whatsoever, picking up the story where James Greenway [11], one of the sources cited by Ziswiler, left off:

    “The only explanation yet put forward for the extinction of L. p. grandis is that of Bond (1936, 1956), who suggested the bird’s demise resulted from heavy predation by Green Monkeys (Cercopithecus aethiops) which were introduced on St. Kitts. Greenway (1958) noted that this hypothesis appears weak because the related Lesser Antillean Bullfinch (L. noctis) has survived disturbance by the same monkeys on Barbados (indeed, L. noctis thrives on St. Kitts itself); he further suggested that “Other unknown factors may have been involved.” Greenway, however, did not propose an alternative hypothesis. I shall examine the often-quoted monkey hypothesis and suggest an alternative explanation.” [12]

    Readers interested in the details of the “often-quoted monkey hypothesis” will want to download the PDF. The short answer is: two hurricanes during August 1899 were “probably enough to eliminate L. p. grandis.” [12]

Extinction Is (Not) Forever
Perhaps the most surprising finding, though, is that two of the species Ziswiler claims were driven to extinction by feral cats—the Aukland Islands rail and the Eyrean grass-wren—turn out not to be extinct at all.

  • Aukland Islands rail (Rallus muelleri; Lewinia muelleri)
    Location: Aukland Islands
    Cause (Ziswiler): feral cats
    What we know now: “It was once thought to be extinct but was rediscovered on Adams Island (100 km2) in 1966 and Disappointment Island (4 km2) in 1993… Population numbers are apparently stable.  Although both rail-inhabited islands are predator-free, Auckland Island (a few hundred metres from Adams) supports feral cats, mice and pigs, and therefore the introduction of these animals is a possible threat.” (BirdLife International)
  • Eyrean grass-wren (Amytornis goyderi)
    Location: Australia
    Cause (Ziswiler): feral cats
    What we know now: “Although this species may have a restricted range, it is not believed to approach the thresholds for Vulnerable under the range size criterion… the population trend criterion… [or] the population size criterion… For these reasons the species is evaluated as Least Concern.” (BirdLife International)

Plenty of Blame to Go Around
The remaining 25 extinctions, while not as dramatic as some of those already mentioned, illustrate very well complexities generally lost to those who blindly cite the 33 extinctions (reason enough, they seem to argue, to outlaw the feeding of feral cats and TNR programs everywhere).

  • Iwo Jima rail (Poliolimnas cinereus brevipes)
    Location: Iwo Jima
    Cause (Ziswiler): rats and feral cats
    What we know now: “Due to an increasing human population on Naka from 1910 onwards, its habitat degraded, and natural water sources became scarce. Therefore, the birds had to depend on water tanks near houses in the dry season, where they were easily caught by feral or domestic cats. The last birds collected for science were in 1911 (the 12 birds of the type-series of brevipes), and the last bird seen was in 1920–1925 (Greenway 1967).” (Zoological Museum Amsterdam)

  • Bonin night heron (Nycticorax caledonicus crassirostris)
    Location: Bonin Islands
    Cause (Ziswiler): “habitat altered through civilization or monocultures” and feral cats
    What we know now: “The most likely reason for its extinction is predation by rats and feral cats. However, collectors fascinated by its plumes may also have been responsible; birds shot for use in millinery (a burgeoning business in contemporary Japan) would not have ended up in scientific collections… The Bonin Night Heron became extinct only 50 years after its description. The last specimen was taken in 1889 on Nakōdo-jima.” (Wikipedia)
  • Red-billed rail (Rallus pacificus)
    Location: Tahiti
    Cause (Ziswiler): rats and feral cats
    What we know now: “It was flightless, and its extinction was presumably caused by introduced cats and rats… there were reports from Tahiti until 1844, and from the nearby Mehetia until the 1930s.(BirdLife International)
  • Chatham Island banded rail (Rallus dieffenbachii)
    Location: Chatham Island
    Cause (Ziswiler): feral cats and rats
    What we know now: “Its extinction was presumably due to predation by introduced rats, cats and dogs, and habitat loss from fire… The species was already scarce when the type was collected in 1840, and was extinct by 1872.” (BirdLife International)
  • Samoa wood rail (Pareudiastes pacificus; Gallinula pacifica)
    Location: Samoa
    Cause (Ziswiler): feral cats and rats
    What we know now: “Cats, rats, pigs and dogs have no doubt contributed to its disappearance, and hunting may also have been a factor as it was formerly a favoured food of the human population… it was last recorded in 1873. In 1984 there were two possible sightings in upland forest west of Mt Elietoga, and in October 2003 a possible sighting of two individuals was made at 990 m on Mount Sili Sili. A recent survey of the island yielded no record of the species.” (BirdLife International)
  • Jamaica Pauraque (Siphonornis americanus americanus; Siphonorhis americana)
    Location: Jamaica
    Cause (Ziswiler): feral cats and “mongoose forms”
    What we know now: “This species has not been recorded since 1860, and it may have been driven to extinction by introduced mongooses and rats, whose effect may have been exacerbated by habitat destruction. However, it cannot yet be presumed to be Extinct because there have been recent unconfirmed reports, and surveys may possibly have overlooked this nocturnal species. Any remaining population is likely to be tiny, and for these reasons it is treated as Critically Endangered (Possibly Extinct).” (BirdLife International)

    Note: there is no mention of cats at all.

  • Lord Howe grey-headed blackbird (Turdus poliocephalus vinitinctus)
    Location: Lord Howe Island
    Cause (Ziswiler): feral cats and feral pigs
    What we know now: “It was quite common in 1906 but its population began to diminish in 1913 due to disturbance by man, cats, dogs, goats and feral pigs. When the SS Makambo was shipwrecked on Lord Howe in June 1918 rats escaped from the vessel and overran the island. With other endemic bird species this ground-nesting bird became extinct within six years.” (Wikipedia)
  • Raiatea thrush (Turdus ulietensis)
    Location: Society Islands
    Cause (Ziswiler): feral cats and rats
    What we know now: “Raiatea was visited in 1850 by explorer and natural history collector Andrew Garrett, who failed to record the species. Evidently it became extinct between 1774 and 1850, almost certainly as a consequence of the inadvertent introduction of Black or Brown Rats to the island.” (Wikipedia)

    Again, no mention of cats.

  • Kittlitz’s thrush (Zoothera terrestris)
    Bonin Islands
    Cause (Ziswiler): feral cats and rats
    What we know now: “Whalers started to use the island in the 1830s and it was probably driven to extinction by introduced rats and cats shortly after.” (BirdLife International)
  • Hawaiian honeycreepers (16 forms)
    Location: Hawaii
    Cause (Ziswiler): “habitat altered through destruction of the forest,” “habitat altered through civilization or monocultures,” and feral cats
    What we know now: “Some 20 species of Hawaiian honeycreeper have become extinct in the recent past, and many more in earlier times, between the arrival of arrival of the Polynesians who introduced the first rats, chickens, pigs, dogs, and hunted and converted habitat for agriculture.” (Wikipedia)

    Also: “The birds face a host of hungry new arrivals such as rats, cats, and pigs, as well as the age-old problem of habitat destruction. But their main enemy was the arrival of avian malaria in the 1940s.” (The Cornell Lab of Ornithology)

•     •     •

So, how many avian extinctions have cats caused? I don’t know.

Then again, neither do Butler, the authors of the UNL paper, Dauphine, or any of the others who suggest they do—and then use that “knowledge” to fuel the witch-hunt against free-roaming cats.

It’s funny how the same people who make so much noise about the U.S. population of pet cats tripling over the past 40 years (without acknowledging the increasing likelihood that these cats are indoor-only, of course) have demonstrated no interest at all in updating their island extinctions factoid.

Then again, they only rarely acknowledge the fact that the extinctions occurred on islands, or the fact that feral cats were just one of many contributing factors. In those instances where cats were involved at all—and where birds were actually driven to extinction.

Considering what these people are proposing—the wholesale killing of cats by the tens of millions—is it really too much to ask that they do a little more fact-checking and a little less Kool-Aid drinking?

Literature Cited
1. Butler, K., “Faster, Pussycat! Kill! Kill!” Mother Jones. 2011. July/August. p. 72–73.

2. Hildreth, A.M., Vantassel, S.M., and Hygnstrom, S.E., Feral Cats and Their Managment. 2010, University of Nebraska-Lincoln Extension: Lincoln, NE.

3. Dauphine, N. and Cooper, R.J., Impacts of Free-ranging Domestic Cats (Felis catus) on birds in the United States: A review of recent research with conservation and management recommendations, in Fourth International Partners in Flight Conference: Tundra to Tropics. 2009. p. 205–219.

4. Nogales, M., et al., “A Review of Feral Cat Eradication on Islands.” Conservation Biology. 2004. 18(2): p. 310–319.

5. Fitzgerald, B.M. and Turner, D.C., Hunting Behaviour of domestic cats and their impact on prey populations, in The Domestic Cat: The biology of its behaviour, D.C. Turner and P.P.G. Bateson, Editors. 2000, Cambridge University Press: Cambridge, U.K.; New York. p. 151–175.

6. Lever, C., Naturalized animals: The ecology of successfully introduced species. 1994, London: T & A.D. Poyser Natural History.

7. Jackson, J.A., Alleviating Problems of Competition, Predation, Parasitism, and Disease in Endangered Birds: A Review, in Endangered Birds: Management Techniques for Preserving Threatened Species, S.A. Temple, Editor. 1977, The University of Wisconsin Press: Madison. p. 75–84.

8. Galbreath, R., “The tale of the lighthouse-keeper’s cat: Discovery and extinction of the Stephens Island wren (Traversia lyalli).” Notornis. 2004. 51: p. 193–200.

9. Taylor, R.H., “How the Macquarie Island Parakeet Became Extinct.” New Zealand Journal of Ecology. 1979. 2: p. 42–45.

10. Bergstrom, D.M., et al., “Indirect effects of invasive species removal devastate World Heritage Island.” Journal of Applied Ecology. 2009. 46(1): p. 73–81.

11. Greenway, J.C., Extinct and vanishing birds of the world. 1958, American Committee for International Wild Life Protection.

12. Raffaele, H.A., “Comments on the extinction of Loxigilla portoricensis grandis in Saint Kitts.” Condor. 1977. 79: p. 389–390.

Video Games

Northern mockingbirdNorthern mockingbird. Photo courtesy of Wikimedia Commons and Ken Thomas.

“I thought the cats probably really hammered them when they were fledglings,” said former University of Florida doctoral student Christine Stracey in a press release about her study of Northern mockingbirds, “but when they were in the nests, I didn’t really expect the cats to be a huge problem. But I was really wrong about that.”

So, how big a problem are “the cats,” exactly?

No doubt it depends who you ask. But even Stracey, now an assistant professor of biology at Westminster College in Salt Lake City, seems to have rather different opinions on the matter.

In a paper documenting her research, to be published in Biological Conservation, Stracey readily acknowledges the limitations of her work:

“Before we can fully understand the role of nest predation in shaping urban bird communities, we need studies of a suite of species that do and do not thrive in urban environments and we need to study how predator diets change on a rural-urban gradient.” [1]

In the press release, however, Stracey’s not nearly so reserved: “We don’t see any reason why cats wouldn’t also eat cardinal nestlings, brown thrashers, towhees—anything else that is nesting in similar locations.” Noting that some of the cats caught on camera were wearing collars, she warns:

“People should not let their cats roam outdoors at all, but at the very least, keeping them inside at night will cut down on nest predation. Beyond that, we need to think hard about the feral cat problem.”

No wonder the story was picked up so enthusiastically by science sites (e.g., “To Kill a Mockingbird, Just Get a Cat” and “Cats No. 1 Predator to Urban Mockingbird Nests”).

While I agree completely that “we need to think hard about the feral cat problem,” I’m not convinced by Stracey’s work that cats are having any appreciable impact on the population of Gainesville’s Northern mockingbirds—never mind “anything else that is nesting in similar locations.” Indeed, Stracey herself describes the Northern mockingbird as an “urban winner,” and a “native species that is able to not only live with us, but do really well living with us.”

Well, which is it?

The Study
Stracey’s Biological Conservation paper combines the results of her work videotaping nest predators with data from 2005 and 2006, when she and her advisor, Scott Robinson, “documented [without the use of cameras] reduced nest predation in urban habitats at many of the same study sites.” [1]

The later work, conducted for her PhD thesis, involved collecting “data on nest predation rates at seven study sites (two parking lots, three residential neighborhoods, two pastures, and one wildlife preserve) in areas in and around Gainesville, FL between February and August of 2007–2008.” [1] In 2009, “one of the residential neighborhoods, one of the parking lots, and one of the pastures” were not included. [1]

Over this same period, Stracey used video cameras (clips are available at her Website) mounted at several nest locations (eight in 2007, 52 in 2008, and 84 in 2009) “to compare the identity of nest predators at nests in the urban matrix and non-urban habitats.” [1] Which, presumably, will shed light on the generally accepted urban nest predator paradox, which Stracey describes as the “mismatch between predation rates, which are often lower in urban areas, and predator abundance, which is often higher in urban areas.” [1]

In other words: if there are so many more predators is urban areas, why do predation levels tend to be lower?

Nest Survival
Using the logistic exposure method, Stracey calculated daily survival rates for Northern mockingbird nests for each habitat and each year of her study.

Here, the daily survival rate (DSR) is a measure of the odds that the eggs or nestlings will remain in the nest from one day to the next. A DSR of 90 percent, for example, means there’s a 90 percent chance—or nine-to-one odds—of a nest surviving from day to day. Or, to put it another way, there’s a 10 percent chance that the nest’s contents will be destroyed by a predator. (More generally, DSR includes any nest “failure,” but because Stracey was interested in predation, she “only considered nests that failed due to predation as ‘unsuccessful,’ thus her “daily survival rates… are not a measure of overall nest survival, but rather the probability of a nest escaping predation.’’ [1])

Nine-to-one odds sound great if you’re in Las Vegas, but no winning streak lasts forever. Over the course of the entire nest cycle, even a DSR of 96 or 97 percent takes its toll.

In the case of the Northern mockingbird, it takes about 13 days for the eggs to hatch and another 12 for the subsequent nestling stage. [2] (At least this is what Fischer found working in south Texas; Stracey doesn’t go into such details in her paper.) A DSR of 97 yields a 46.7 percent nest survival rate; a DSR of 96, only 36 percent (and this doesn’t take into account the additional “3 to 5 days for nest construction [and] 3 to 5 days for egg laying” observed by Fischer, who found that “a successful nest was used for an average of 33 days.” [2])

Assuming (conservatively) that there was essentially no risk of predation prior to the eggs being hatched, I used Stracey’s DSR data and a nest cycle of 25 days to estimate nest survival rates. (I also reordered the data to better compare habitats year-to-year.)

The result illustrates three important points:

  1. The residential neighborhoods—the only sites where cats were observed predating nests (more on that shortly)—are safer than either of the non-urban sites (the two pastures and the wildlife preserve) during 2005 and 2006, when cameras weren’t in use. (While I’m not suggesting that this difference is the result of the cameras, I’m not convinced that the cameras were as impartial as Stracey would have us believe—this, too, will be addressed shortly.) Indeed, even during 2007–2009, the results are, at best, mixed.
  2. The wildlife preserve, contrary to what its name suggests, fails to “outperform” the other habitats’ nest survival rates across all five years—sometimes (as in 2005, when the rate was just over 14 percent) spectacularly.
  3. Perhaps the most striking result, though, is the nest survival rates of Stracey’s two parking lot sites, which, in every year but 2008, top those of the other habitats—two to four times the rates documented at the wildlife preserve in some years. “Urban winner” is right. With apologies to Joni Mitchell, then, perhaps the best thing for the mockingbirds is to pave paradise and put up a parking lot.

Strong Nest Predators
My interest in Stracey’s work has less to do with nest survival itself, and much more to do with the role of cats in nest failure. Of the 24 predation events caught on tape in the residential neighborhoods, 17 (71 percent) were attributed to cats. By contrast, no cats were observed predating nests in the pastures or at the nature preserve. There, Cooper’s hawks were responsible for 15 of 33 (45 percent) predation events taking place at occupied nests. (One abandoned nest was raided by a blue jay.)

“I found no evidence,” writes Stracey, “that urban areas provide a refuge from strong nest predators.” [1]

“The strongest predator, cats, were essentially only found in urban areas, and Cooper’s hawks, the dominant predator in rural habitats, were found at roughly the same abundance in the two habitats (pers. obs.)… These results suggest that simple considerations of predator abundance do not explain habitat-specific patterns of nest predation.” [1]

Dig into the details of Stracey’s study, though, and it becomes clear that she’s probably overestimating the strength of cats as urban predators. In fact, her camera placement (intentionally or not) almost certainly biased her data.

Stracey didn’t use nest cameras in the parking lots “for fear of theft,” [1] a perfectly reasonable concession, but that means excluding approximately 36 percent (according to my calculations) of “urban” nest predation from her “whodunit” data set. And it’s easy to imagine that predation at these sites was skewed heavily toward predators other than cats (probably birds).

In terms of identifying individual predators, then, “urban” habitats include only residential neighborhoods.

Stracey also eliminated as candidates for video cameras 21 (7 percent) nests located more than 4 meters (approximately 13 feet) off the ground. These nests would seem to be largely inaccessible to cats. Similarly, she eliminated 18 of 124 (14.5 percent) of nests “located in trees that were right on the edge of a sidewalk or street that did not afford a place to hide the set-up.” [1] Again, perfectly understandable, but this almost certainly biased her results.

In short, it seems Stracey observed predation by cats largely because she placed the cameras where the cats were.

In addition to the 58 events caught on camera, “22 predation events were missed due to problems with the camera set-up, including drained batteries and damaged wires.” [1] Whether or not these incidents were evenly distributed across the three different habitats isn’t clear, and the implications could be significant.

As it is, the majority (58.6 percent) of videotaped predation occurred at non-urban sites; had the bulk of the technical problems (which accounted for 27.5 percent of the 80 predation events Stracey had the opportunity to videotape) also occurred at those sites, Stracey would have a more difficult time concluding, as she does, that “urban areas clearly do not provide a generalized refuge from nest predators.” [1]

Or maybe not. Even if Cooper’s hawks accounted for twice the nest predation as cats, I suspect the focus would merely shift from absolute predation rates to predation by non-native predators.

And finally there’s the question of whether the nest cameras had any effect on predation levels. Stracey says they didn’t, but it appears that she simply compared failure rates for nests with and without cameras for each year the cameras were in use.

Richardson et al. (whose work Stracey cites) point out that “expression of neophobia and wariness among larger mammals, corvids, and raptors is likely to differ according to the extent to which those predators have been persecuted [inline citations omitted]. Such variation should be considered when interpreting the results of camera studies from different habitats and among different groups of nest predators.” [3, emphasis mine]

“Although camera equipment at nests likely does attract the attention of generalist predators, we propose that many predators may not respond positively to these potentially novel objects. Some small rodents, in particular, can be highly neophobic, reacting to novel stimuli with extreme caution and often avoidance (Barnett and Cowan 1976, Innes 1978). Though seemingly fearless and inquisitive, wild corvids likewise can be highly neophobic, particularly toward objects that do not resemble natural food items (Coppinger 1969, Heinrich et al. 1995), which may explain why Thompson et al. (1999), expecting to document nest predation by American crows and blue jays based on their abundance at the study site and their reputation as nest predators, did not record predation by any corvids. Raptors may exhibit a degree of neophobia as well (Ruggiero et al. 1979). Both canids and corvids have demonstrated aversion toward remote camera equipment, possibly driven more by wariness of human activity than generalized neophobia (Hernandez et al. 1997, Harris and Knowlton 2001, Herranz et al. 2002, Sequin et al. 2003). For nest studies using remote cameras, neophobia may be reinforced by the fact that camera equipment is seldom left in place for >2 weeks. As nests fail or fledge, camera equipment is relocated to active nests at new locations.” [3]

To illustrate what they mean by persecution, Richardson et al. cite the work of Herranz et al. (one of those in-line citations omitted above): “In our study area, Black-billed Magpies are shot and trapped by hunters, and this may increase their awareness of strange objects in the environment.” [4]

It seems reasonable, then, to expect that cats—the most “welcome” (especially those kept as pets) of the predators in Stracey’s study—would also be the least neophobic. (Though, of course, from a historical perspective, cats are arguably the most persecuted of the lot.)

It may well be, then, that Stracey caught more cats on camera largely because (1) the cameras were located—literally—in the cats’ backyards, and (2) the cats weren’t put off by the equipment.

•     •     •

I asked Stracey about all of this by way of e-mail, but received no response. My follow-up e-mail also went unanswered, but I did notice some Website traffic from the Salt Lake City area that same day. Of course, it could be nothing more than coincidence.

The same can be said for the traffic I saw from Columbus, OH, late last week on the same day I contacted Dr. Amanda Rodewald, professor of wildlife ecology at Ohio State University. From what I can tell, Rodewald had nothing to do with Stracey’s mockingbird study; nevertheless, she was quoted in the UF press release:

“There are a lot of loud voices that deny cats are important predators of birds in our cities… But this study shows clearly that cats were the dominant predator in this Florida system—and that wasn’t presumed, it was recorded on video, so it was fact.”

So, I sent Rodewald an e-mail—identifying myself as one of those “loud voices.” I explained that I wasn’t asking her to speak for Stracey, nor to defend the research. But, given her own research interest—and her obvious concern with Stracey’s work—perhaps she might be able to answer one question for me: What impact might we expect on the area’s Northern mockingbird populations if the cats were removed from the environment?

No response yet—though it’s only been a few days. Still, I’m not holding my breath.

Literature Cited
1.  Stracey, C.M., “Resolving the urban nest predator paradox: The role of alternative foods for nest predators.” Biological Conservation. 2011. In Press, Corrected Proof.

2. Fischer, D.H., “Factors Affecting the Reproductive Success of the Northern Mockingbird in South Texas.” The Southwestern Naturalist. 1981. 26(3): p. 289–293.

3. Richardson, T.W., Gardali, T., and Jenkins, S.H., “Review and Meta-Analysis of Camera Effects on Avian Nest Success.” Journal of Wildlife Management. 2009. 73(2): p. 287–293.

4. Herranz, J., Yanes, M., and Suárez, F., “Does photo-monitoring affect nest predation? Journal of Field Ornithology. 2002. 73(1): p. 97–101.[0097:DPMANP]2.0.CO;2

The Daily Show’s Take on the Cat-Bird Debate

Screenshot--The Daily Show

By now, many—perhaps most—readers have already seen the segment of Monday night’s episode of The Daily Show with Jon Stewart in which correspondent Aasif Mandvi satirized the cat-bird debate (described all too accurately, I’m afraid, by Mandvi as an “intractable war”).

Interviewed for the piece were American Bird Conservancy president George Fenwick and Alley Cat Allies president Becky Robinson (the cats’ “moneyed lobbyist,” as Mandvi explained, tongue firmly in cheek), while Jackson Galaxy’s contribution was, sadly, reduced to little more than a cameo.

I can’t imagine Fenwick’s pleased with how he came off, but perhaps he should be counting his blessings.

Frankly, I’d like to have seen Fenwick in the hot seat—Jim Kramer-style—defending his talking points (e.g., “cats are super-predators, especially when it comes to birds,” “cats kill hundreds of millions of birds,” etc.) to an unsympathetic Stewart.