The expansion of the eastern house finch population and its impact on populations of house sparrows, purple finches and American goldfinches
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Abstract
Houses Finches became a breeding species in Indiana in 1981 and subsequently went through a rapid population increase. This study was an investigation of the growth of the House Finch population and its impact on House Sparrows, American Goldfinches and Purple Finches in Indiana. Data from the Annual Christmas Bird Counts of the National Audubon Society (CBC) were used to construct five winter range maps to show the expansion of the House Finch population since 1940. A population density map based on the CBCs of 1988 and 1989 was constructed using birds counted per party hour.CBC data collected during 1965 to 1989 at twelve locations in Indiana were used to track long-term changes in the populations of House Finches, House Sparrows, American Goldfinches and Purple Finches. The number of House Finches counted in Indiana since 1981 increased dramatically. The size of the House Sparrow population appears to have been in a long-term decline for the last 25 years. However, American Goldfinches have, in general, increased in abundance since 1979. The abundance of Purple Finches in Indiana in the winter varies erratically.Observations at backyard feeding stations frequented by House Finches and House Sparrows show that House Finches tend to displace other House Finches more often than would be expected if the displacements occurred in proportion to the frequency at which the birds appear in the population. House Sparrows were found to displace other House Sparrows at a rate which greatly exceeded the expected frequency based on their proportion of the population. Both species tend to avoid interspecific interactions.Field studies in Muncie, Indiana show that House Finches commonly nest in shrubbery and building decorations while House Sparrows often nest in crevices in old buildings and bird houses. No direct competition for nesting sites was observed.Banding studies indicate that during the fall and winter there is a constant turnover of House Finches in Muncie. Using banding data from the U. S. Fish and Wildlife Service it was found that House Finches in the Midwest tend to travel in a southern direction as the season changes from summer to winter and in a northern direction as the season changes from winter to summer. The study shows that House Finches have a strong propensity to return to the same general area each summer.