Nest Predation and Its Relationship to Habitat and Nest Density in Dickcissels

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Abstract
Analysis of the histories of over 500 dickcissel (S. americana) nests found in eastern Kansas [USA] 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 chambers 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.