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Birds of Indian Subcontinent

Flying the Gantlet: Population Characteristics, Sampling Bias, and Migration Routes of Eared Grebes Downed in the Utah Desert

Publication Type:Journal Article
Year of Publication:1999
Authors:Jehl, Jr., JR, Henry, AE, Bond, SI
Journal:The Auk
Volume:116
Issue:1
Date Published:1999
ISBN Number:00048038
Keywords:bias, Great Salt Lake, Mexico, Podiceps, Podiceps nigricollis, Podicipedidae
Abstract:In January 1997, an estimated 35,000 Eared Grebes (Podiceps nigricollis), about 3% of the population that stages at Great Salt Lake, Utah, were downed by snowstorms while migrating between Great Salt Lake and Mexico. Another 920 grebes crashed on the north-bound migration in late March 1997. We examined 1,500 carcasses to determine the characteristics of the population during fall versus spring migration with regard to age and sex ratios, body mass, plumage abnormalities, presence of parasites, and morphological defects. In many cases, large samples derived from mass downings provide a reasonable index of the composition of birds aloft. However, we found important differences in sex ratios between two samples derived from the same flight, which indicates that assumptions regarding unbiased sampling require testing. The possibility that regular catastrophic events in central and southern Utah have influenced the evolution of migration routes in Eared Grebes deserves further consideration.
URL:http://www.jstor.org/stable/4089464
Short Title:The Auk
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