“Invasive” Feral Cats Aren’t So Bad After All

These days, almost everyone involved with trying to increase live release rates for cats supports Trap-Neuter-Return (TNR) and Return-To-Field (RTF) programs for community cats. The barriers still in the way of TNR and RTF include old-fashioned ordinances in a lot of localities, and bird conservationists. Advocates for cats are chipping away at the ordinances, but the conservationists are stubborn. Many of them argue that all cats should be kept indoors and that any cat found outdoors should be captured and killed.

One of the arguments made by the conservationists is that cats have no place in the outdoors in the United States because they are an “invasive” species (also called “non-native”  or “alien”). Cats first came to the Americas in ships from Europe many centuries ago. The conservationists argue that non-native species such as cats destroy native wildlife because the native wildlife species have not evolved ways to protect themselves from the invaders. The idea that invasive species are bad is deeply ingrained in conservation biology, and it has been a difficult argument for cat advocates to address.

A new book by science journalist Fred Pearce calls the traditional thinking about invasive species into question. The book, “The New Wild: Why Invasive Species Will Be Nature’s Salvation” (Beacon Press, 2015), uses the term “green xenophobia” to refer to what Pearce considers to be an overblown concern about damage done by invasive species, and a failure to appreciate their value and their place in nature. He argues that the success of roaming species can be seen as a positive counterweight to environmental destruction caused by humans.

One of the non-native species that Pearce mentions is the cat. He challenges a cost-benefit analysis made by one scientist that purported to show that cats cost the United States economy $30 for every bird they kill, or $17 billion total each year. The $17 billion number itself is questionable, but Pearce points out that the considerable benefits to the economy that are provided by cats, including rodent control and the documented health benefits to people who have pet companions, were not weighed against the $17 billion figure.

Pearce has an interesting discussion of the unintended consequences of efforts to control invasive species on Macquarie Island, a remote island between Australia and Antarctica that is a nesting place for seabirds. The first invaders on Macquarie Island were rats who had stowed away on sealers’ ships. Then cats were brought in to control the rats, and rabbits were brought in for food for the sealers. Many years later the rabbits were eating a lot of the island’s vegetation, so conservationists wiped out most of the rabbits by introducing a disease. But then the cats, with few rabbits to hunt, started killing the birds. The cats were shot, and then the rats, with no cats to control their population, ate the birds. Meanwhile, the remaining rabbits, with the cats no longer there to keep them in check, began to multiply again. (Today the invasives are thought to be gone, but how long will that last?)

Much of the evidence that conservation biologists cite in an attempt to prove that invasive species cause damage to native species comes from islands like Macquarie. It is true that there have been some dramatic examples of bird extinctions caused or aided by non-native species on islands. Pearce notes, however, that new studies indicate that plant diversity of ocean islands usually rises after “invasions” by alien species, even in cases where the number of birds declined.

Moreover, what happens on islands cannot and should not be generalized to mainlands. Cat advocates for years now have been pointing out the weaknesses in the argument made by conservationists that cats are doing damage to birds at the species level on the United States mainland. This important new book supports the arguments that have been made by advocates, but it goes beyond them in arguing that the success of invasive species is an example of the power of nature to change and adapt. Something to be welcomed, perhaps, rather than feared.

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