Felines Fatales
by Ted Williams
November 2009
The American Bird Conservancy estimates that 150 million free-ranging cats kill 500 million birds each year in the United States.
The University of Hawaii is overrun by feral house cats. They are fed by university professors and students, who also trap and medicate them, get them spayed and castrated, then release them. The idea is that the colony will eventually die out without individuals being subjected to the perceived hideous fate of euthanasia. Pioneered in North America at the University of Washington in the 1980s, the practice is called Trap, Neuter, and Return (TNR). It has become popular across the United States. But the evidence suggests it does not work.
My guide was Rachel Neville, manager of the Oahu Invasive Species Committee, which has accomplished the monumental task of ridding the island of coquí frogs from Puerto Rico. Her chances of ridding Oahu of feral cats: essentially zero. On this island alone there are about 1,200 registered feral-cat colony caregivers. From July 1, 2007 to June 30, 2008, the Hawaiian Humane Society sterilized 2,573 feral cats at no charge for 461 people. That sounds impressive until you consider that between 71 percent and 94 percent of a colony would have to be sterilized before its numbers could decline—assuming there is no immigration—and that at least 100,000 feral cats are believed to live on the island. Moreover, it is nearly as hard to trap cats as it is to herd them, and welfare programs for feral cats encourage the dumping of unwanted pets.
Wildlife biologists and law-enforcement officials contend that in many situations feeding feral cats violates federal law because it facilitates the “take” of species protected by the Migratory Bird Treaty Act and the Endangered Species Act.
The toll on wildlife is immense. The American Bird Conservancy estimates that 150 million free-ranging cats kill 500 million birds each year in the United States. A peer-reviewed study published February 24, 2009 in Conservation Biology found that TNR programs can lead to “hyperpredation,” in which well-fed cats continue to prey on bird, mammal, reptile, and amphibian populations so depressed they can no longer sustain native predators.
Feral cats can accelerate the extinction process. On Hawaii’s Big Island, for example, they destroy roughly one out of every ten nests of the endangered Palila, a native honeycreeper. At elevations of 10,000 feet on Mauna Loa, cats take endangered Hawaiian Petrels from their burrows. These seabirds produce only a single chick, which cannot fly for 15 weeks, and adults do not begin breeding until they are at least five years old.
On Kauai, threatened Newell’s Shearwaters become disoriented by artificial lights and crash to the ground. Usually they are unhurt, but because they cannot take off from land, people collect them and place them in special “mailboxes” at fire stations from which they are returned to the sea. Increasingly, however, feral cats congregate under the lights and kill the birds before they can be rescued.
On Maui, where the public maintains more than one hundred feral cat colonies, two cats killed 143 Wedge-tailed Shearwaters in a single night. These birds lay only one egg a year after reaching seven years of age, and if one parent is killed the chick dies. One study found Hawaiian Stilt remains in 12 percent of examined feral cat stomachs.
Scott Fisher of the Maui Coastal Land Trust points out that seabird guano once enriched coastal wetlands throughout Hawaii. With seabird populations declining, alien plants are increasingly taking over these habitats. When biologist Fern Duvall of the Hawaii Division of Forestry and Wildlife compared seabird nesting success on the main islands with that on offshore islands where cats were absent, he found 13 percent nesting success on the former and 83 percent on the latter.
Ted Williams is Editor-at-Large for Audubon magazine. This article was condensed, with permission, from the September–October 2009 issue.