Experimental Study of Predation on Eggs of Ground-Nesting Birds: Effects of Habitat and Nest Distribution

Predation pressure on nests of ground-nesting birds was examined experimentally by offering predators artificial nests with small, white chicken eggs in three adjacent habitats: marsh, wet meadow, and upland thicket. In each habitat, 40 nests with eggs were distributed in three 80- × 80-m quadrats according to random, uniform, and clumped distribution patterns and nests were examined for predation on days 5 and 10. In three sets of experiments during which each quadrat in each habitat received all nest distribution treatments, predation rates were highest in the upland thicket, intermediate in the wet meadow, and generally low in the marsh. The pattern of nest distribution consistently affected predation rates in the upland thicket only, where the uniform distribution resulted in lower predation. In the upland thicket many predators were responsible for high predation and unpredictable predation patterns which presumably favor spacing out (uniform nest distribution) in this habitat. In contrast, low predation in the marsh, resulting from exclusion of many predators, appears to be unimportant in determining spatial distribution of marsh-nesting birds.