Band-tailed pigeons in Woodside, Portola Valley, Los Gatos and Saratoga are dying. A parasite -- avian trichomoniasis -- is making its way through the band-tailed population, often through contaminated water in birdbaths, according to the California Department of Fish and Wildlife.
It's happening now because the pigeons, which are native to the West Coast, flock around this time of year, bringing them into close proximity with one another and making it convenient for the parasite to spread, said state wildlife biologist Krysta Rogers. Once infected, the band-tail quickly dies.
Other bird species may encounter the parasite but not fall ill. Trichomoniasis is "fairly bird-species-specific," Ms. Rogers said.
The band-tail pigeon is dark gray with bright yellow legs and beak and without the wide band of iridescent feathers that circle the neck of the city-dwelling rock pigeon.
Recent reports of dead band-tails in Los Gatos and Portola Valley led the state to declare an outbreak, Ms. Rogers said. Why those two communities? They aren't exactly neighbors. "As the pigeon flies, they're close," she said.
Birdbaths are suspected to be a transmission catalyst. The parasite lives in and may escape from band-tails' mouths when they drink, perhaps infecting other pigeons drinking the now-infected water, according to the National Wildlife Health Center in Madison, Wisconsin, an agency of the U.S. Geological Survey.
Birdbaths should be drained and not refilled, Ms. Rogers said, adding that feeding or providing water for wild birds, even in a drought, is a bad idea. It brings unfamiliar birds together and increases the likelihood of diseases spreading. "Wild birds are capable of finding food on their own. They can survive without handouts from people," she said.
Band-tails avoid bird feeders in that they prefer acorns, particularly those of the coast live oak. The birds swallow them whole, she said.
Feeding wild birds "comes with a lot of responsibility," she added. About twice a week, feeders and water containers should be thoroughly washed with soap and water and then decontaminated with a 10 percent bleach solution. Using the bleach without first washing the object will undermine the cleansing effect of the bleach.
If you see a sick or dead bird in your yard, to break the disease cycle, you should stop feeding altogether for at least two weeks, Ms. Rogers said.
One bird species believed to carry and spread the parasite while staying immune to its toxicity is the rock pigeon, that annoying orange-eyed denizen of sidewalks and ledges in cities around the world.
If you see a rock pigeon in your yard, in the interest of "biological security," you should treat it as an unwelcome guest, particularly if you have chickens, she said.