"From my personal experience as Palo Alto park ranger for over a decade, I have personally seen feral cats hunt and catch birds in the Baylands Nature Preserve," said Daren Anderson, the city's division manager of open space, parks and golf.
Not only do feral cats kill mammals, reptiles, insects and birds, they also eat their eggs and can spread diseases. They also compete for prey with other predators, who shift to hunting endangered species, he said.
It's unknown how many feral cats live in the Baylands, but 14 endangered, threatened and sensitive wildlife species, including the California clapper rail and salt marsh harvest mouse, are affected by the cats, wildlife officials said.
The populations of the Baylands' endangered species are shrinking. In 2011, about 14 clapper rails were found there; as many as 19 are known to exist at Palo Alto Harbor and Hooks Island, according to a 2011 Point Reyes Bird Observatory Conservation Science report. Those numbers are down from 2010, when the Baylands had as many as 22 of the birds.
No one knows how many salt-marsh harvest mice live in the Baylands, but they too are being devoured by cats and other predators, Anderson said.
Ann Nussbaum, a volunteer with the Palo Alto Humane Society, disagreed with wildlife experts' view that feral cats are killing the wildlife at any significant rate.
"Many people blame feral cats for being predators and accuse them of hurting the bird population. The real problem is habitat loss, pollution and pesticide use. Humans are the top predators. Studies show that feral cats do their hunting at night and much prefer rodents to birds," she said.
She defended the program that feeds the feral cats, known as "trap, neuter, release."
"When they are fed in neutered, managed colonies, they are not starving and have less impulse to hunt at all. Compared to people, the damage feral cats do is minor," she said.
Because the feral cats are spayed and neutered, the program actually reduces the number of cats over time, she added. The Stanford Cat Network reduced the university's population of feral cats from 1,500 to an estimated 25 or 35, feeding-program proponents have said.
But Anderson said he has seen an increase in the cat population in Palo Alto's open space.
"Feral-cat feeding stations, which leave large quantities of cat food in park and open space areas, lure in other stray cats, and encourage people who are looking for a place to abandon their cats to choose that site. I've personally caught dozens of people dropping off a variety of animals — dogs, ducks, roosters, turtles, rabbits and cats — at the Baylands Duck Pond because they thought it was a site where people would feed them," he said.
At any rate, wildlife experts say, cats are not native animals, and they have no place in refuges where there are endangered and threatened species.
Doug Cordell, spokesman for the U.S. Fish and Wildlife Service's San Francisco Bay National Wildlife Refuge Complex, said the argument that fed cats don't hunt wildlife doesn't hold up. Remote cameras show feral cats hunting and catching endangered species near the feeding stations. Postmortems have found remains of endangered species in their stomachs, according to research by the Fish and Wildlife Service and U.S. Geological Survey.
A two-year study by the East Bay Regional Parks in two grassland parks found that cats had a significant impact on wildlife. One park had no cats; the other had more than 20 cats, who were fed daily. Scientists saw almost twice as many birds in the park with no cats. California thrasher and California quail were found in the cat-free area; the birds were never seen in the park with cats.
More than 85 percent of the native deer mice and harvest mice that researchers trapped were in the catless park. In contrast, 79 percent of house mice, an exotic pest species that had replaced the native species, were found in the area that had cats.
Anderson said city staff is researching the best ways to handle the feral cats.
Trapping and euthanizing cats that cannot be adopted out is one method. But wildlife experts are exploring cutting into berms. The method would inundate areas with water so predators don't have access into marshes, according to a California Coastal Conservancy clapper-rail habitat plan.
The City Council this fall will consider adopting the ban on feeding wildlife and feral cats in city parks and open-space preserves.
Threatened/sensitive/endangered species found in Palo Alto open space:
Black-crowned night heron
California clapper rail
Pygmy blue butterfly
Salt marsh harvest mouse
Threatened/sensitive/endangered species rarely found in Palo Alto open space:
California brown pelican
California least tern
California tiger salamander
Western snowy plover