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Nesting Biology of Dickcissels and Henslow's Sparrows in Southwestern Missouri Prairie Fragments
The Wilson Bulletin
Vol. 111, No. 4 (Dec., 1999), pp. 515-526
Published by: Wilson Ornithological Society
Stable URL: http://www.jstor.org/stable/4164137
Page Count: 12
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According to data from the North American Breeding Bird Survey, populations of Dickcissel (Spiza americana) and Henslow's Sparrow (Ammodramus henslowii) have declined severely during the last 30 years. The reasons for their population declines seem to differ; habitat fragmentation on the breeding grounds has been suggested to have little negative impact on Dickcissels, but appears to be a major reason for Henslow's Sparrow declines. Previous reports on the status of Dickcissels and Henslow's Sparrows largely were based on density estimates without considering the nesting biology of the two species. My comparison of the nesting biology of Dickcissel and Henslow's Sparrow provides some insight into potential factors that might contribute to their population declines. During 1995-1997, I studied the nesting biology of Dickcissels and Henslow's Sparrows in fragments of native tallgrass prairie in southwestern Missouri. Both species had similar clutch sizes, rates of hatching success, and numbers of young fledged per successful nest. Dickcissels tended to have lower rates of nesting success and higher rates of brood parasitism by Brown-headed Cowbirds (Molothrus ater) than Henslow's Sparrows. Although several vegetation characteristics at the nest differed between successful and depredated nests in Dickcissels, no differences were found between successful and depredated Henslow's Sparrow nests or between parasitized and unparasitized Dickcissel nests. My results indicate that Dickcissels might reproduce less successfully than Henslow's Sparrows in southwestern Missouri, and might therefore be of higher conservation concern on the breeding ground than previously thought.
The Wilson Bulletin © 1999 Wilson Ornithological Society