Nesting success of a disturbance-dependent songbird on different kinds of edges

We compared the nesting success of a disturbance-dependent species, the Indigo Bunting (Passerina cyanea), on different kinds of habitat edges in five sites (225 total nests) in southern Illinois from 1989 to 1993. Nest predation rates along agricultural and abrupt, permanent edges (e.g., wildlife openings, campgrounds) were nearly twice as high as rates along more gradual edges where plant succession was allowed to occur (e.g., treefalls, streamsides, gaps created by selective logging). Levels of brood parasitism by Brown-beaded Cowbirds (Molothrus ater) varied significantly among sites and years, but not among edge types. Clutch sizes, however, were significantly smaller at agricultural edges where nest predation rates were also high, which suggests either decreased food availability or a population dominated by younger and/or lower-quality (poor condition) birds. The results of this study illustrate the need to reevaluate management practices (e.g., wildlife openings) that are designed to promote populations of disturbance-dependent wildlife.