Preliminary Test of the Ecological Trap Hypothesis

Abstract

We tested factors associated with predation near forest-field edge and with the ecological trap hypothesis using artificial bird nests containing Japanese quail (Coturnix japonica) eggs. Predation rates were determined for 759 nests placed in a systematic pattern within plots perpendicular to a forest-field ecotone created by commercial timber harvest in northern Idaho. One plot contained an abrupt edge and 1 contained a wide feathered edge of partial timber removal. Nests of 2 diameters (80 and 100 mm) were located on the ground and above ground in shrubs, and were placed in high- (20 nests/ha) and low-density (9 nests/ha) patterns. No difference was detected for predation rate with respect to nest location or size. Nests placed in a low-density pattern received higher percent predation than nests in a high-density pattern. The high-density plot had greater shrub cover, which may have restricted predator effectiveness. Predation rates were >4× higher in forest plots than field plots; these results may reflect relatively infrequent use of field subplots by avian predators requiring perch sites. Our data do not support the ecological trap hypothesis; we found no relationship between distance from edge and predation rate. However, our abrupt-edge subplots had higher predation than the feathered-edge subplots. These data support earlier hypotheses that birds are poorly adapted to abrupt, artificial-edge habitats, and that these habitats may have a barrier effect and create a travel lane for predators. CR - Copyright © 1988 Wiley