Domestic Cat Predation in California

Background

Most of California's threatened or endangered birds and land mammals are vulnerable to domestic cat predation. Although loss and fragmentation of habitat due to human development are the main causes of wildlife population declines, large numbers of pet, stray, and feral cats roaming the remaining habitat is a serious concern. Compounding this problem are the people and organizations who insist on maintaining cats in parks or adjacent to other sensitive wildlife areas (see "Managed" Cat Colonies in California). The following studies show effects of cat predation on some of California's native wildlife.

Cat Predation Studies in California

Cats can impact California Quail populations. Photo: Alan Hopkins

East Bay Regional Park District:  A two-year study was conducted in two grassland parks in the East Bay Regional Park District. One park had no cats, but over 20 cats were fed daily in the other park. Almost twice as many birds were seen in the park with no cats as in the park with cats. California Thrasher and California Quail, common ground-nesting birds, were seen in the no-cat area, but were never seen in the cat area. In addition, over 85 percent of the native deer mice and harvest mice trapped were in the no-cat area, whereas 79 percent of the house mice, an exotic pest species, were found in the cat area. Most likely, the cat food was supporting the house mice in that park. Native deer and harvest mice are important in maintaining the native grassland habitat. According to Dr. Cole Hawkins who conducted the study, "Cats at artificially high densities, sustained by supplemental feeding, reduced the abundance of native rodent and bird populations, changed the rodent species composition, and may have facilitated the expansion of the house mouse into new areas. Thus . . . the feeding of cats in parks should be strictly prohibited."

Scrub-breeding birds such as the Greater Roadrunner can be impacted by cats. Photo: Peter LaTourette

San Diego: In studying the relationships between coyote, mid-sized predators such as cats, and scrub-dwelling birds, a survey was conducted of cat owners living along the rims of steep-sided canyons to determine the amount and type of prey their free-roaming cats brought home. These canyons are isolated fragments of habitat with many endemic species (occuring nowhere else). Survey respondents reported that on average, each outdoor cat that hunted returned 24 rodents, 15 birds, and 17 lizards to the residence each year. Researcher Dr. Kevin Crooks estimates, ". . . that all the cats living along the rim of a moderately-sized canyon . . . return about 840 rodents, 525 birds, and 595 lizards to residences each year." "This level of bird predation appears to be unsustainable." The study also found that in small canyons where the coyote was absent, there was an increase in mid-sized predators such as cats, raccoons, and opossum, and a drastic decline in diversity, and in some cases elimination, of scrub breeding birds such as Cactus Wren, California Gnatcatcher, and Greater Roadrunner. However, in larger canyons where coyotes were still present, scrub-breeding birds were also seen.

Rare Species Vulnerable to Cat Predation in California

Domestic cat predation is most critical for the following state and federally listed threatened and endangered species. See the U.S. Fish and Wildlife Service Endangered Species web site for more information about each species.

Snowy Plover. Photo: Don Baccus

Birds:
Light-footed Clapper Rail, Rallus longirostris levipes
California Clapper Rail, Rallus longirostris obsoletus
California Least Tern, Sterna antillarum browni
Western Snowy Plover, Charadrius alexandrinus nivosus
California Brown Pelican, Pelecanus occidentalis californicus
California Gnatcatcher, Polioptila californica
San Clemente Loggerhead Shrike, Lanius ludovicianus mearnsi

Mammals:
Pacific Pocket Mouse, Perognathus longimembris pacificus
Stephens' Kangaroo Rat, Dipodomys stephensi
Morro Bay Kangaroo Rat, Dipdomys heermanni morroensis
Point Arena Mountain Beaver, Aplodontia rufa nigra

Reptiles:
Island Night Lizard, Xantusia riversiana
Blunt-nosed Leopard Lizard, Gambelia silas
Alameda Whipsnake, Masticophis lateralis euryxanthus

Cats and Disease Transmission

Domestic cats are carriers of many diseases and parasites, some of which can be transmitted to other cats, wildlife or humans, such as rabies, roundworm, fleas, and plague. Cats are suspected of spreading Feline leukemia virus (FeLV), and Feline infectious peritonitis (FIP) to mountain lion in California. FeLV is the leading cause of death due to infectious disease in cats. Cats are also the source of the parasite, Toxoplasma gondii, which causes a brain infection deadly to endangered California sea otters. Researchers believe the parasite spreads as outdoor cats’ feces, laden with millions of parasite oocysts (eggs), wash into the ocean from streams and drainage ditches. The oocysts are then absorbed by filter-feeding shellfish that are food for the otters. A recent study found that 42% of live otters and 62% of dead otters tested positive for T gondii. For more information on diseases and parasites of cats, see The Great Outdoors is no Place for Cats.

Further Information

"Managed" Cat Colonies in California

California Department of Fish and Game

References