An intensive, three-year feral cat eradication project on remote San Nicholas Island is complete, and has been deemed successful according to partners in conservation directly involved with the felines’ removal.

Located 61 miles off the Ventura County coastline, the distant, windswept isle has been owned by the U.S. Navy since 1933, and feral cat control has been a long-term endeavor. The island has a long history of feral populations, including goats and dogs. The cats were the last of the feral populations to go. Over time they’ve had a negative impact on land and seabird populations and island night lizards. They also were in direct competition with endemic island foxes, a federally protected species.

The Montrose Settlements Trustee Council contributed $3 million to the project, working jointly with the U.S. Navy, Island Conservation, Institute for Wildlife Studies (IWS) and the Humane Society of the United States.

“The cats were utilizing the entire island, from coast to coast, and the interior plateaus,” said Chad Hanson, project manager for Island Conservation. “They were particularly active during nesting season.”

Over the years the nests of western snowy plovers, Brandt’s cormorants, western gulls, black oystercatchers and horned larks have been easy targets for feral cats. They also preyed on sluggish island night lizards, and competed with island foxes for similar prey items and denning sites. The threat of rabies and other diseases being spread to island foxes was also a concern.

Following five years of project planning from 2004 through 2008, and completion of the final environmental assessment in May 2009, Island Conservation and IWS began using camera traps across the 14,562-acre island that June. From there, they implemented padded leg-hold live traps. The feral cats were trapped, then transported off the island to a rehabilitation facility designed by the Humane Society in Ramona in San Diego County.

More than 70 islands around the world have successfully removed feral cat populations. San Nicholas, however, is the largest island in the world for successful cat eradication without the use of a toxicant, and the largest island in the U.S. to complete a cat eradication project.

“Feral cats proved to be more ravenous, more aggressive than island foxes,” explained Dave Garcelon, president of IWS, who has worked extensively in the recovery of California Channel Islands species for 30 years.

A makeshift hospital was built on the island in case any cats or island foxes were injured during trappings. Island foxes are similar in size to feral cats and were sometimes accidentally trapped. A total of 1,011 fox captures took place during the feral cat eradication project.

“Feral cats aren’t much different than bobcats,” continued Garcelon. “They weren’t real happy about being in captivity.”

Cats were likely brought to the island as pets and for pest control in the early 1900s, during the island’s ranching era. By the 1950s large numbers of feral cats were roaming the 9-mile-long, 3.5-mile-wide island.

By the time Island Conservation and IWS took on trapping duties, a total of 66 cats were removed. Ten kittens were transferred off the island and adopted. The other cats are being rehabilitated and in time will be up for adoption. The last cat detected and removed was in June 2010, but monitoring continued until December 2011.

“They were very feral,” said Kim D’Amico, a wildlife care specialist for the Humane Society. “They’ve become accustomed to humans and have grown more friendly. This is the first time we’ve done anything like this off an island.”