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Nest Predation and Its Relationship to Habitat and Nest Density in Dickcissels
John L. Zimmerman
Vol. 86, No. 1 (Feb., 1984), pp. 68-72
Published by: American Ornithological Society
Stable URL: http://www.jstor.org/stable/1367348
Page Count: 5
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Analysis of the histories of over 500 Dickcissel (Spiza americana) nests found in eastern Kansas showed that those in old-field habitats suffered more predation than those in prairies. Predation rates on the prairie, were not correlated with the weeks of the nesting season, but those in old-fields varied significantly with time. Although both predation rates and nest densities increased concurrently to a peak during the middle of the nesting season in old-fields, an analysis of the relationship between nest densities per week and both daily predation rates and the percent of nests lost to predators each week indicated that predation was not density-dependent. Predation rates are higher in old-fields than in prairies, not because of greater nest densities, but perhaps because predators are more abundant in old-fields. Snakes are the most probable nest predator, and their method of hunting, by chance encounters rather than by directed search, is suited to the absence of a density-dependent effect of predation on Dickcissel nests.
The Condor © 1984 Cooper Ornithological Society