ANTIOCH -- Skulking around the edges of parking lots and trash bins or lingering behind restaurants, feral cats seem to be everywhere, with estimates on their numbers ranging into the tens of millions nationally. And no one is quite sure how to get rid of them.
In the Bay Area, some government agencies have started working with animal rescue groups using a decades-old method of population control and say they are making headway. Others insist the approach is doing as much harm as good.
"It's a more humane approach, and more economical," said Jon Cicirelli, San Jose's deputy director of Animal Care and Services and a leading proponent of the practice known as "trap, neuter and release."
"Trap, neuter and release" -- TNR, to those in the know -- is an alternative to euthanasia, which is often the fate of cats whose wild temperaments make them unadoptable.
San Jose's animal shelter fixes the ownerless cats it receives, then turns them over to a nonprofit, which returns them to the wild.
Detractors argue that while the practice may stop feral cats from reproducing, they are still hard-wired to hunt. Releasing these animals back to environmentally sensitive areas enables them to continue preying on wildlife.
A national study published in January in the journal Nature Communications ramped up the debate between cat lovers and conservationists with its rough estimates that outdoor cats -- most of them feral -- kill from 1.4 billion to 3.7 billion birds and billions of wild mammals annually and as such are likely these creatures' biggest threat.
But Cicirelli says "trap, neuter and release" is working. Since the San Jose shelter adopted the practice three years ago, it has reduced its intake of cats by 25 percent. He also points to the number of dead cats his agency removes from city streets: That number has dropped by 17 percent in the past three years.
Santa Clara County's shelter, which works with the Humane Society of Silicon Valley, reports similar results: Whereas the facility euthanized 382 feral cats in 2009, the kill count dropped to zero last year, and the number of strays it takes in has dropped by nearly 25 percent since the partnership was established.
However, TNR's critics point out that it's difficult to wipe out even a single colony. Plenty of ferals are still out there to breed, and their numbers are bolstered because people are always abandoning cats.
Antioch restaurant owner Sheila White earlier this year confronted a woman after seeing her dump feral cats by the city's former boat launch ramp. The woman tearfully confessed that the cats her neighbor feeds had spilled onto her property, and she no longer could care for their kittens or cope with them using her yard as a bathroom, but she didn't want them killed at a shelter.
Indeed, 48 percent of the 940 cats that Antioch Animal Services euthanized last year couldn't be handled safely. The vast majority of them were feral.
Others focus on the welfare of wildlife.
A two-year study in the East Bay Regional Park District -- an area where about five dozen species are rare or have been declining -- found a marked difference between the number of birds in an area of a park that feral cats frequented and the number where there were no cats. Ample research shows feral cats kill native wildlife at a faster rate than non-native species, according to wildlife biologist Dave Riensche.
David Jessup, a former senior wildlife biologist with the state Department of Fish and Wildlife, strongly objects to feral cat groups that promote neutering ferals as the only answer.
Communities also should find homes for ferals tame enough to be adopted and place those that aren't in enclosures where colony feeders can care for them, he said.
"Look at all the tools available," he said. "(TNR) is being sold by its advocates as the only morally acceptable solution, and it simply isn't."
Reducing the number of feral cats requires a multipronged approach, agreed Margaret Slater, senior director of veterinary epidemiology with the American Society for the Prevention of Cruelty to Animals.
Lost pets are among the cats wandering around, so owners should protect theirs with microchips and collar tags, she said.
Pets allowed outside should be neutered so they don't contribute to feral colonies, and communities need to publicize places where owners can surrender a cat knowing that it will be properly cared for, Slater said.
"You've got ignorant people feeding the numbers," said Kathy Condron, a volunteer with the Richmond nonprofit Fix Our Ferals. "People are the cause of the problem -- not the cats. The cats are doing what any animals will do."
Contact Rowena Coetsee at 925-779-7141. Follow her at Twitter.com/RowenaCoetsee.