Environment & Science

Calif.'s only native pigeons dying by the thousands from disease

A band-tailed pigeon perches in a tree at Blue Canyon, CA in July 2013.
A band-tailed pigeon perches in a tree at Blue Canyon, CA in July 2013.
Krysta Rogers
A band-tailed pigeon perches in a tree at Blue Canyon, CA in July 2013.
A sick band-tailed pigeon in Los Gatos, CA in January 2015.
Krysta Rogers

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During one of the worst winters on record for California's only native species of pigeons, they are dying of disease, and state officials are seeking the public's help to monitor the disease’s progression and remove transmission sources from their yards.

The band-tailed pigeon, the only pigeon native to California, is especially susceptible to avian trichomonosis, a disease caused by a single-cell protozoan called Trichomonas gallinae.

The protozoan is believed to have co-evolved with the common rock pigeon, which was introduced from Europe. It causes lesions to form in infected birds’ mouths and throats. The birds, which subsist largely on acorns that they swallow whole, are unable to move food down their throats and starve or can even suffocate.

A state scientist said the ongoing drought may be aiding in the disease’s transmission among the band-tailed pigeon population.

“These mortality events seem to occur more frequently in winters with lower precipitation, so it’s certainly possible that the mortality events that we’re seeing this winter are related to drought conditions,” said Krysta Rogers, an environmental scientist with the California Department of Fish and Wildlife.

The drought has reduced the number of available water sources, thereby concentrating the numbers of birds at remaining watering holes.

“Anytime you have a small volume of water and lots of band-tailed pigeons utilizing it, if there is this parasite circulating within the population, it can spread more rapidly in that close contact,” Rogers said.

Rogers gave a rough estimate that as many as 10,000 band-tailed pigeons have died in California this winter as a result of the disease. Hard numbers are difficult to produce, because birds are difficult to monitor. Current estimates of the disease’s impact are based on reports of dead birds submitted by the public.

Rogers said the department is continuing to ask for citizens to report on sick or dead birds that they find.

The department is also asking for residents to remove feeders, birdbaths and fountains until the pigeons leave their wintering grounds. Rogers said that it’s unclear whether past calls for restricting the features have aided in disease control but that the request is logical.

“I can’t really put a number on whether or not it helps, because I don’t know if people are actually doing it or not,” Rogers said. “I think it’s one of the easiest things that can be done. If that bird feeder and that bird bath aren’t available for wild birds, then disease transmission definitely will not happen there.”