State wildlife authorities on Tuesday asked that bird baths and feeders in residential yards be taken down in an effort to stem the spread of a parasite that is taking a heavy toll on California's only native pigeon.
Necropsies on the carcasses of Pacific Coast band-tailed pigeons collected since December at locations from the Bay Area to San Diego determined they were infected with the protozoa responsible for avian trichomonosis, said Krysta Rogers, an environmental scientist with the California Department of Fish and Wildlife.
The parasite, which scientists know as Trichomonas gallinae, lives in the mouth and throat of infected birds, causing lesions that block the passage of food and air. Infected birds typically die from starvation or suffocation.
The non-native urban pigeon is thought to be the main source of infection for the band-tailed pigeon, a migratory game bird that winters in California. But state veterinarians are also concerned about the risk of spillover to hawks, falcons and owls that prey on pigeons.
Bird feeders and artificial water sources may increase transmission of the disease because they bring band-tailed pigeons in close contact with other birds.
"We're recommending that residents not feed or water wild birds while the pigeons are wintering here," Rogers said. "But if they must, we ask that they make sure their birdbaths and feeders are cleaned well and regularly."
In Southern California, band-tailed pigeon carcasses have been reported in oak and conifer forests in Santa Barbara and Los Angeles counties, and in the San Bernardino Mountains.
"As a precautionary measure, we drained a large pond on our grounds," said David Myers, executive director of the nonprofit Wildlands Conservancy, which is headquartered in the San Bernardino County community of Oak Glen. "We've also sent nine pigeon carcasses to state wildlife officials for inspection."
Epidemics of trichomonosis involving tens of thousands of band-tailed pigeons have been sporadic in California since 1945. Research suggests they tend to occur more often in warmer, drier winters, state officials said.
There were two reported trichomonosis events between the early 1950s and early 1980s, officials said. Over the last decade, however, there have been six such events.
The overall population of the reclusive pigeons with purplish heads and breasts, dark-tipped yellow bills, yellow legs and broad gray tail bands has been in steady decline since the 1940s, according to annual surveys and takes reported by hunters.