EFFECTS OF OLFACTORY ATTRIBUTES AND SIZE OF EGG ON RATES OF PREDATION OF ARTIFICIAL GROUND NESTS IN TALLGRASS PRAIRIE

Abstract

We examined influence of type of nest, olfactory attributes of nests, and size of egg on rates of predation of artificial ground nests in a tallgrass prairie site in Oklahoma during 1998–1999. Our objective was to investigate the role that odors of nests might play in predation of artificial grassland nests. In the first experiment, using eggs of the house sparrow (Passer domesticus) as bait, rates of predation on artificial reed nests purchased commercially were compared to artificial grass nests constructed from on-site vegetation. Rate of predation did not differ between type of nest. A second experiment tested effects of the odor of nests that mimicked presence of an incubating female. Artificial nests baited with eggs of the house sparrow were used with one-half being lined with 25–35 feathers from an adult house sparrow, and half being allocated no feathers. Overall depredation did not differ between these types of nest. In a third experiment, which tested effects of novel odors on predation, artificial nests were baited with either painted or unpainted eggs of the house sparrow. Nests with both types of eggs were depredated heavily (70–75% losses). A final experiment tested effects of size of egg by comparing predation among nests baited with eggs of the house sparrow, northern bobwhite (Colinus virginianus), or domestic chicken (Gallus gallus). Nests with eggs of the house sparrow (smaller eggs) were preyed upon significantly more (75% cumulative losses) than nests with either eggs of the northern bobwhite or domestic chicken (both with 5% cumulative losses). Although our observed rates of predation on artificial nests were similar to those from studies of predation of both artificial and natural ground nests, our results indicated that odors associated with artificial nests were unimportant relative to size of egg with respect to predation at this grassland site.