![]() ![]() They declined to just 231 birds in 2012.Īlthough it's unclear whether blackbirds are dwindling across Southern California in general or whether the foot disease plays a role, Unitt said it's a piece of the puzzle. Starting in the 1990s, the numbers dropped to about 500. Counts in the 1980s consistently logged more than 1,000 Brewer's blackbirds, and in some years recorded several thousand of the gregarious, flocking birds. The San Diego Audubon Christmas Bird Count, a popular annual bird survey that Unitt helps coordinate, shows a steady decline. ![]() "When you look at the landscape of things going on in wildlife, you're going to focus on things that cause mortality rather than nonfatal foot problems," Rideout said.Ī chronic condition can become catastrophic, however, if other factors - such as changes in habitat, predation or other pathogens - set the stage for decline.īrewer's blackbird is a common species that visits suburban lawns, parking lots and shopping malls, Unitt said.īut the bird's everyday visibility may belie its health. Think West Nile virus and bird flu, which are both potentially lethal to birds and people, or Bluetongue disease, which kills deer and livestock. With limited resources, researchers target the most egregious plagues - those that cause mass die-offs or wreak havoc on humans and domestic animals in addition to wildlife. Unidentified wildlife diseases aren't unheard of, Rideout said. Molecular analysis of their tissue samples could help pinpoint a cause, he said. To solve the mystery, he said, he'd need to see live birds with sick feet. However, he cautioned: "None of these scenarios are a perfect fit with your descriptions and the high (affliction rate) you are seeing." Any number of contagions or contaminants could cause the lesions, he wrote in an e-mail to colleagues: avian pox or viral infection with secondary bacterial invasion, scaly leg mites, chronic irritation complicated by bacterial or fungal infections, exposure to caustic chemicals and blood parasites that constrict small blood vessels. ![]()
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