A Comparison of Predation Rates on Real and Artificial Nests of Grassland Birds

I compared rates of predation between real and artificial nests of grassland birds in order to test the impact of nest type, nest position, and egg size on predation rates. I distributed wicker avicultural baskets and realistic grass nests baited with a clay egg and either northern bobwhite (Colinus virginianus) or house sparrow (Passer domesticus) eggs in four Conservation Reserve Program (CRP) grasslands in east-central Illinois. Nest success averaged 86.5% for 12 days of exposure for artificial nests. For real nests, nest success was markedly lower; averaging 39% over the entire nesting cycle and 59% during approximately 12 days of incubation. Wicker nests were depredated more often than realistic grass artificial nests (18% versus 8%), and nests baited with house sparrow eggs were depredated more often than nests baited with quail eggs (22% versus 9%). Elevated and ground nests were depredated at the same rate. No edge effects were detected for real or artificial nests at road, rowcrop, or wooded edges. Patterns of nest predation on wicker nests were markedly different from depredation patterns on real nests over time and among fields. In contrast, patterns of nest predation on realistic grass artificial nests corresponded much more closely with predation rates of real nests over time and among fields. I suggest that future artificial nest studies use nests and eggs that mimic as closely as possible the real nests and eggs of target species. Use of unrealistic artificial nests and eggs, at least in grasslands, may result in patterns of predation that do not accurately reflect the variation in predation rates over time and locations for real nests