Does Vertical Partitioning of Nest Sites Decrease Nest Predation?

Abstract

Partitioning of nest heights among co-occurring species in response to nest predation has been proposed as a process that helps to structure avian species assemblages. In the experiment reported here, we used artificial nests baited with Japanese Quail (Coturnix japonica) eggs to test (1) whether both rate and final level of nest predation differed among nests placed at ground, shrub, and tree strata; and (2) whether vertical partitioning of nest sites among the three strata decreased nest predation. Although rates of nest predation increased from ground, to partitioned, to shrub, to tree strata, the only significant pairwise differences were between predation on ground nests versus all other treatments. The proportion of nests depredated at the conclusion of the experiment was lowest for the ground treatment, intermediate for the partitioned treatment, and highest for the shrub and tree treatments. Predation was significantly higher in 1988 than in 1989, and significant variation in predation occurred among five spatial replicates of the experimental treatments. Although the results show different susceptibilities to nest predation according to vegetative stratum, they show only a slight and nonsignificant reduction in nest predation as a consequence of vertical nest-site partitioning.