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.


Cats and Birds