Tuesday, March 3, 2015

House Finch

Here are a male and female House Finch at the feeder last Saturday. It is hard to remember that this species, now one of the most numerous birds across the United States, southern Canada, and Mexico, was unknown in the East before 1939. Then caged birds either escaped or were released from a New York City pet store. They quickly expanded their range across the continent. Curiously, at the same time, House Finches expanded out of their desert southwestern range. Although a House Finch thought to be an escaped cage bird was discovered in Minneapolis in 1896, birds from the current expansion appeared in the state in the early 1980s (Janssen 1987).

In 1994, House Finches were super abundant across the country and found in almost every conceivable habitat. Then the species was struck by an outbreak of mycoplasmosis, a bacteria that formed grotesque pustules around finch eyes, bills, and feet.  Several species of mycoplasma bacteria also attack poultry, causing serious respiratory infections. Others infect people, resulting in pneumonia and pelvic inflammation. We bird banders were never thrilled to handle infected House Finches. Banding recoveries, however, demonstrate that the disease is not invariably fatal to birds.

Millions of House Finches died, and, in some areas, local populations disappeared. This disease has been called one of the “worst epizootics in history” (Badyaev et al. 2012). Other species, like goldfinches, occasionally showed symptoms, but not with the same devastating destruction of populations. One hypothesis is that eastern House Finches, since they originated from those few New York birds, were genetically less robust than western birds, and, thus, were exceptionally susceptible to the bacteria. Genetic studies demonstrate western birds do, indeed, have significantly greater genetic diversity than eastern ones.

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