Why killing cats on remote islands will not help biodiversity

And why killing dogs, rats,  pigs,  goats,  mice & mongooses too would be mainly make-work for exterminators

            SANTA CRUZ,  California––Appealing for funding to kill cats,  dogs,  rats,  pigs,  goats,  and mongooses on at least 107 islands belonging to 34 nations,  in the name of promoting biodiversity,  the previously obscure 25-year-old organization Island Conservation scored a double coup on March 27,  2019.

First,  the appeal concept,  a paper entitled “Globally important islands where eradicating invasive mammals will benefit highly threatened vertebrates,”  was published by the Public Library of Science online journal PLOS One.  This lent the imprimatur of science to what is in truth a values-based argument for a make-work project on behalf of at least some of the authors,  and a shaky argument at that.

Scare tactics

Second,  the PLOS One paper was abstracted and globally amplified by mass media under headlines such as “Should cats be culled to stop extinctions?,”  the version offered by Helen Briggs of BBC News.

Such headlines framed the paper as generations of cat-hating birders have framed the underlying arguments since the 19th century,  as a matter of cats and a handful of other species allegedly jeopardizing biodiversity,  mostly of rare birds.

This argument has long been a big fundraiser for organizations such as the American Bird Conservancy.  It may be an effective scare tactic among people who have not already taken sides,  pro-cat or anti-cat,  at a time when the notion that we are in the midst of a so-called “Sixth Extinction” enjoys general currency and is seldom challenged in mass media except by climate change denialists.

The first premise is wrong

Yet the “Sixth Extinction” hypothesis,  popularized by entomologist E.O. Wilson in 1997,  was and is wholly based on mathematical modeling,  using input data now decades obsolete.

Over the 22 years since then,  the numbers of identified species have exponentially increased,  the numbers of known extinctions have been dwarfed by the numbers of rediscoveries of species believed to have been extinct,  and––despite well-publicized declines of large,  charismatic megafauna in the oceans and Southern Hemisphere––net biodiversity has increased on every continent if one counts non-native species.

Which are the majority of species in most habitats.

Self-serving economic arguments

For several generations now,  most arguments against doing things to protect endangered species and prevent a supposed “Sixth Extinction” have been based not on refuting the weak arguments that a “Sixth Extinction” is happening in the first place,  or considering that the recommended responses may not be effective,  but instead on self-serving short-term cost/benefit analyses advanced by various ecologically destructive industries,  hellbent on escaping regulation.

The self-serving nature of most of the arguments made against controversial approaches to protecting endangered species,  always offered in contexts involving economic interests,  superficially seems to lend moral force to arguments for undertaking drastic measures immediately,  to prevent the catastrophe presumably looming,  even if the drastic measures might accomplish nothing at all.

Concealed self-interest

The purported urgent need to respond to the alleged “extinction crisis” meanwhile obscures the reality that the people and organizations pushing drastic measures also tend to have a significant economic interest as stake.  Saving endangered species is in itself a big business,  involving billions of dollars and tens of thousands of workers.

Killing island populations of cats,  dogs,  rats,  pigs,  goats,  and mongooses by any means possible,  no matter how ecologically destructive the methods may be,  is a drastic measure,  employing lots of technicians and scientists,  but not really well-considered,  even as a means of saving biodiversity in the specific habitat where the killing is done.

New Zealand

A case in point is the ongoing saturation of New Zealand forests with the pesticide Compound 1080,  as part of a national putsch against “invasive predators” that is in truth designed to diminish biodiversity by exterminating “non-native” mammals,  including brush possums,  cats,  rats,  and rabbits,  to benefit “native” birds.

Not all mammals are targeted,  however.  Livestock and hoofed species favored by hunters are supposedly exempt,  regardless of their considerable impact on bird habitat.

But it is not really possible to exterminate one category of animal with mass deployment of a broad-spectrum pesticide without catastrophically harming others.

Killed 98% of non-target deer

An investigation commissioned by the Marlborough branch of the New Zealand Deerstalkers Association on March 21,  2019 extracted from the New Zealand Department of Conservation an admission that an October 2017 deployment of Compound 1080 over a highland farm called Molesworth Station killed 97% of the non-target deer there,  perhaps as many as 4,000.

Undeterred,  the New Zealand Department of Conservation authorized a scheme to kill 300 feral Himalayan tahr,  an endangered species in their native habitat,  to feed to kea,  a native carrion-eating parrot,  while keas’ usual prey is depleted in the wake of Compound 1080 drops in the hills behind Whataroa.

Ironically,  kea became scarce in the first place because farmers persecuted them as seasonal lamb predators,  and the New Zealand government even paid bounties on them.

Focal points of paper can backfire

Fourteen people are listed as co-authors of “Globally important islands where eradicating invasive mammals will benefit highly threatened vertebrates.”

Altogether,  “Fifty authors representing more than forty institutions from around the world contributed to publishing this paper,”  according to Island Conservation publicist Sally Esposito.

The paper is long,  as PLOS One papers go,  at 6,194 words,  but if 14 people were genuinely co-authors,  their average contribution was about half a page;  if 50 people contributed,  their average contribution might have been just a paragraph.

Among all this claimed input,  none of the participants seem to have realized that their focal points could be turned around and cited as arguments for not funding their intended extermination campaign,  even if their input data is accepted without dispute.

75% of extinctions have occurred on islands

Most of “Globally important islands where eradicating invasive mammals will benefit highly threatened vertebrates” is unfortunately written with the quotable fluency of gravel rattling out of a dump truck.  Publicist Esposito,  however,  in her media statement did a reasonably good job of translating the noise into English.

Compiling the paper was led,  Esposito said,  “by conservation biologists from Island Conservation,  the Coastal & Conservation Action Laboratory at the University of California at Santa Cruz,  BirdLife International,  and the International Union for the Conservation of Nature Species Survival Commission Invasive Species Specialist Group.

“There are approximately 465,000 islands in the world,”  Esposito summarized in bullet point, “yet they comprise just 5.3% of the Earth’s terrestrial area.  Islands have hosted 75% of known bird,  mammal,  amphibian and reptile extinctions since 1500.

Critical refuges?

“Islands provide critical refuges for highly-threatened species,”  Esposito continued,  “currently supporting 36% of bird,  mammal,  amphibian and reptile species that are classified as Critically Endangered on the IUCN Red List.”

Not acknowledged is that many and perhaps most of these species occupy habitat so limited that they were probably critically endangered from the beginning of their existence.

“Many islands’ species are threatened as a direct consequence of invasive alien species,”  Esposito paraphrased.  “Cats and rats are the most damaging invasive species known on islands,”  a comment taking surprisingly little notice of human activity.

Average success rate of 85%?

The paper,  “Globally important islands where eradicating invasive mammals will benefit highly threatened vertebrates,”  contends,  Esposito said,  that “Eradication of invasive mammals from islands is a proven conservation tool”;  “more than 1,200 invasive mammal eradications have been attempted on islands worldwide,  with an average success rate of 85%”;  and that “Larger more remote and technically challenging islands are being successfully cleared of invasive species populations each year.”

All of this is contradicted by other scientific literature favoring eradication of “invasive species,”  especially cats and rats.

For example,  “A Review of Feral Cat Eradication on Islands,”  by eight co-authors,  published in 2004 in the journal Conservation Biology,  lamented that while feral cats had been extirpated from 48 islands in 30 years of effort,  “cats have been successfully removed from only 10 islands larger than 10 square kilometers in size,”  representing a 21% success rate.

To be sure,  though,  the efficiency of cat purges may have improved over the past 15 years.

Exterminating four species to maybe save five,  for a while

“Globally important islands where eradicating invasive mammals will benefit highly threatened vertebrates,”  added Esposito,  “highlighted restoration opportunities including Floreana Island, Galápagos Archipelago, Ecuador;  Gough Island, Tristan da Cunha Archipelago,  United Kingdom Overseas Territories; and Alejandro Selkirk Island, Juan Fernandez Archipelago,  Chile.”

According to the paper,  extirpating cats,  rats,  mice,  and goats from these three islands “would remove the threat of non-native predation” allegedly threatening two species of petrel,  one endangered species of albatross,  one critically endangered bunting,  and one critically endangered songbird.

On Floreana Island,  eradicating cats and rats “will also allow for the reintroduction of 13 locally extinct species.”

How 292 islands were narrowed to 107

How was this determined?

Asserts the paper itself,  “Based on extinction risk,  irreplaceability,  severity of impact from invasive species, and technical feasibility of eradication,  we identified and ranked 292 of the most important islands where eradicating invasive mammals would benefit highly threatened vertebrates.

“When socio-political feasibility was considered,  we identified 169 of these islands where eradication planning or operation could be initiated by 2020 or 2030 and would improve the survival prospects of 9.4% of the Earth’s most highly threatened terrestrial insular vertebrates (111 of 1,184 species).

“Of these, 107 islands in 34 countries and territories could have eradication projects initiated by 2020.  Concentrating efforts to eradicate invasive mammals on these 107 islands would benefit 151 populations of 80 highly threatened vertebrates and make a major contribution towards achieving global conservation targets adopted by the world’s nations.”

Predation is usually not the first or greatest threat

Those are bold but largely unsupported claims.  “Globally important islands where eradicating invasive mammals will benefit highly threatened vertebrates” says practically nothing about the many threats to the species at risk from sources other than predation.

And predation is often not the main factor,  if even a factor,  in driving those species to endangerment.

In all likelihood,  factors such as climate change,  diminished gene pools,  loss of food sources, and disease have already condemned most of the critically endangered species to extinction,  regardless of any and all heroic last-ditch measures that might be undertaken on their behalf.

Consider the Bramble Cay melomys

For example,  wrote Countdown to Extinction editor John R. Platt on March 21,  2019,  beneath the headline “Climate Change Claims Its First Mammal Extinction,”  a tiny rodent called the Bramble Cay melomys,  last seen in 2009,   “lived in just a single habitat,  a small reef island at the northern tip of the Great Barrier Reef,  near Papua New Guinea.  The sandy cay—which only measures about 1,100 feet by 500 feet and rises just three feet above sea level—has in recent years been buffeted by storm surges from extreme weather events.  The heavy waters have reportedly wiped out about 97% of the land mass’s vegetation—the melomys’s only source of food.”

Killing such vulnerable species’ predators might buy some of them a little more time,  but they are nonetheless barely hanging on,  in habitat that has substantially changed from the conditions in which they evolved.

Killing cats,  rats,  or goats will not bring back a lost marine food web

Because of global warming,  for instance,  oceanic currents have shifted;  more acidic waters are inhibiting the ability of crustaceans and shellfish to build shells,  but jellyfish are more abundant than they have been in millions of years;  and different plants are favored on the islands in question.  These three factors alone have permanently altered the food webs upon which many critically endangered species depend.

No amount of killing “invasive predators” is going to bring back a lost marine food web.

Not only are remnant species doomed by habitat change,  but reintroducing species to habitat that no longer suits their needs is foredoomed to failure as well,  at significant cost meanwhile in animal suffering.

Meanwhile,  extirpating species who are thriving in the altered habitat in hopes of recovering others who are not,  and likely never will again,  is a cruel exercise in futility.

But suppose the paper’s authors are right?

But,  for the sake of argument,  let us suppose that the authors of “Globally important islands where eradicating invasive mammals will benefit highly threatened vertebrates” are entirely correct in their assessment of how much they could accomplish to preserve vanishing species if funded to kill “invasive predators” to their hearts’ content.

What would this mean,  relative to the greater picture of species and habitat conservation?

The most hostile opponents of endangered species protection,  for example in the energy industry,  might welcome the news,  and even donate toward killing cats,  rats,  dogs,  pigs,  goats,  mice,  and mongooses,  because the purported 9.4% of the world’s most endangered species that the killing might save are not the species interfering with oil drilling,  building pipelines,  clearing rainforests to plant palm oil plantations,  shipping crude oil through treacherous waters,  and operating nuclear reactors.

Endangered species not all equal in ecological importance

Saving that 9.4% of endangered species,  however,  might make an impressive “offset”––on paper––for the loss of perhaps 5% of endangered species as result of reckless mainland and offshore energy development schemes.

Consider,  though,  that the 9.4% of endangered species on the “globally important islands” are all very few in number,  of limited range,  make little contribution to the survival of other species,  and are of miniscule biomass and biological needs compared to the great whales,  grizzly bears,  sage grouse,  orangutans,  and myriad other species put at risk by energy development.

All endangered species are not equal in ecological importance.  Saving the 9.4% spotlighted by “Globally important islands where eradicating invasive mammals will benefit highly threatened vertebrates” could not begin to compensate for the losses to mainland and offshore ecosystems if such trade-offs benefiting industry and economic development were to be made.

Wildlife overpasses

Even excluding the possibility of cynical trade-offs,  however,  the resources available for species and habitat conservation are limited.  Every cent spent to save the 9.4% of endangered species on remote islands from cats,  rats,  dogs,  pigs,  goats,  mice,  and mongooses is a cent not spent to save the other 90.6% of endangered species.

Many of the other 90.6% have a much better prognosis for longterm survival if their critical habitat is protected by relatively simple,  inexpensive,  and less ecologically risky measures––including just not doing things that destroy the habitat.

Dollar for dollar spent,  building wildlife overpasses and purchasing land to enable species including grizzly bears,  bison,  elk,  bighorn sheep,  and pronghorn to migrate safely throughout the Rocky Mountains region,  to cite just one example,  probably has more potential to benefit more species at risk––including all the many small species whose existence depends on the activity of the large,  charismatic megafauna­­––than anything that can be done for island species whose entire habitat is at imminent risk.

Descended from Edward Howe Forbush

In gist,  despite having been published with the trappings of science,  “Globally important islands where eradicating invasive mammals will benefit highly threatened vertebrates” is just the latest of a long series of screeds descended philosophically from the 1916 Edward Howe Forbush tract The Domestic Cat:  Bird Killer,  Mouser & Destroyer of Wild Life;  Means of Utilizing and Controlling It.

Forbush (1858-1929) was a late 19th and early 20th century Massachusetts state ornithologist,  whose enduring influence has been huge,  but whose inveterate hatred of cats was based largely on his own scientific ineptitude.

Blamed cats for gull predation

Among other conspicuous errors, Forbush wrongly blamed cats who were never there in the first place for the decline of roseate terns on Muskeget Island,  off Nantucket.  The predation that Forbush misattributed to cats was later established to have been caused by gull predation.

Forbush also conflated the Quebecois slang term for raccoons,  chat sauvage,  and descriptions of raccoon behavior,  with second hand anecdotal accounts of cat behavior,  and conflated bobcats with domestic cats.

Much that Forbush recommended was attempted,  in the name of saving rare birds,  including killing thousands of cats,  but the recovery of most of those bird species,  including roseate terns,  awaited much better science,  conducted generations later with much less hyperbole.

(See How a birder’s mistakes incited 100 years of cat hatred.)

Paper inadvertently suggests that maybe cats et al are not really a big problem after all

In one sense,  though,  “Globally important islands where eradicating invasive mammals will benefit highly threatened vertebrates” represents a retreat from Forbush,  if perhaps an unwitting retreat.

While ailurophobes from Forbush to the present national policymakers in Australia and New Zealand have argued that cats menace birds and other wildlife anywhere and everywhere,  the authors of “Globally important islands…” expand the purported threat to include dogs,  rats,  goats,  pigs,  mice,  and mongooses,  yet narrow the scene of the alleged crimes to much less than 1% of terrestrial habitat.

This suggests some recognition that these so-called “invasive” species are much less a threat to biodiversity than has been widely advertised,  and are perhaps not really any threat at all.

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