The Greatest Conservation Success Story You’ve Never Heard Of

“From a conservation ecology perspective, the most desirable solution seems clear—remove all free-ranging cats from the landscape by any means necessary.”

Cat Wars: The Devastating Consequences of a Cuddly Killer

Hunters using 12-gauge shotguns killed 809 cats over three “hunting seasons” in 1986–1989 (photo by Kevin Language).


Roughly the size of Tampa, Florida, or Salt Lake City, Utah, Marion Island lies approximately 1,325 miles southeast of Cape Town, in the Indian Ocean. It is the largest island from which cats have been successfully eradicated, a campaign spanning more than 19 years during which an estimated 4,000–5,000 cats were killed. No cat has been seen there since July 1991 [1].

Nearly 33 years later, plans are underway for a new eradication campaign—this time to exterminate the island’s mice.

According to recent news accounts (warning: graphic images), the mice, whose numbers increased dramatically after the cats were exterminated, are literally eating seabirds alive. As a result, seabird recovery hasn’t been nearly as successful as had been hoped [2–4].

So, how did we get here? It wasn’t easy.

During the second phase of the seven-phase campaign, for example, the disease panleukopenia was introduced as this was deemed to be “the most efficient and cost-effective method” for quickly bringing down the island’s cat population [5].

“From July 1975, cats, which up to this point had been live trapped and then killed to obtain samples and measurements, were held captive in custom-made cages on the island to serve as future carriers for the establishment of the disease” [1].

It’s estimated that nearly 2,800 cats were killed over a five-year span from panleukopenia alone [5].

During the final phase of the campaign, 30,000 day-old chicken carcasses were injected with the toxin sodium fluoroacetate and distributed across the island [6].

Despite all the reports associated with the eradication campaign, little has been published regarding its economic costs. The only report I’ve found that mentions cost at all refers vaguely to “millions” having been spent during the first six phases with “more millions” required for the “the final, and most expensive, seventh phase” [4].

And eradication of the mice is expected to cost more than $20 million [4].

Given all this, it’s hardly surprising that TNR opponents never mention Marion Island. Pressed for an alternative, they instead resort to the vague arm waving, clumsy euphemisms, and tired dog whistles we’re all familiar with. Marion Island’s 19-year slog—quite literally, the removal of “all free-ranging cats from the landscape by any means necessary” [7]—is the best example they can point to.

Literature Cited

  1. Bester, M.N.; Bloomer, J.P.; van Aarde, R.J.; Erasmus, B.H.; van Rensburg, P.J.J.; Skinner, J.D.; Howell, P.G.; Naude, T.W. A Review of the Successful Eradication of Feral Cats from Sub-Antarctic Marion Island, Southern Indian Ocean. South African Journal of Wildlife Research 2002, 32, 65–73.
  2. Dilley, B.J.; Schramm, M.; Ryan, P.G. Modest Increases in Densities of Burrow-Nesting Petrels Following the Removal of Cats (Felis Catus) from Marion Island. Polar Biology 2017, 40, 625–637, doi:10.1007/s00300-016-1985-z.
  3. Preston, G.R.; Dilley, B.J.; Cooper, J.; Beaumont, J.; Chauke, L.F.; Chown, S.L.; Devanunthan, N.; Dopolo, M.; Fikizolo, L.; Heine, J.; et al. South Africa Works towards Eradicating Introduced House Mice from Sub-Antarctic Marion Island: The Largest Island yet Attempted for Mice. In Island invasives: Scaling up to meet the challenge: Proceedings of the international conference on island invasives; Veitch, C.R., Clout, M.N., Martin, A.R., Russell, J.C., West, C.J., Eds.; IUCN: Gland, Switzerland, 2019; pp. 40–46.
  4. Huntley, B.J. Marion Island: Birds, Cats, Mice and Men. In Strategic Opportunism: What Works in Africa : Twelve Fundamentals for Conservation Success; Huntley, B.J., Ed.; Springer Nature Switzerland: Cham, 2023; pp. 21–37 ISBN 978-3-031-24880-1.
  5. Bloomer, J.P.; Bester, M.N. Control of Feral Cats on Sub-Antarctic Marion Island, Indian Ocean. Biological Conservation 1992, 60, 211–219.
  6. Bester, M.N.; Bloomer, J.P.; Bartlett, P.A.; Muller, D.D.; Van Rooyen, M.; Buchner, H. Final Eradication of Feral Cats from Sub-Antarctic Marion Island, Southern Indian Ocean. South African Journal of Wildlife Research 2000, 30, 53–57.
  7. Marra, P.P.; Santella, C. Cat Wars: The Devastating Consequences of a Cuddly Killer; Princeton University Press: Princeton, N.J., 2016; ISBN 978-0-691-16741-1.



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