Edge Effects on Nesting Dickcissels (Spiza americana) in Relation to Edge Type of Remnant Tallgrass Prairie in Kansas

Abstract

Edge effects on grassland-nesting birds should be less pronounced or absent near cropland edges of grasslands that lack wooded-edge habitat often used by nest predators and brood parasites. We compared nest predation, brood parasitism and densities of dickcissel (Spiza americana) nests in relation to distance from woodland and cropland edges of Kansas tallgrass prairie. Daily nest predation rates did not differ (P > 0.25) among distance intervals (≤50 m, 51–100 m, ≤100 m and >100 m) from either edge type or among 50-m intervals adjacent to each edge type. Brood parasitism rates by the brown-headed cowbird (Molothrus ater) were higher ≤100 m vs. >100 m from woodland edges (P = 0.04), being highest ≤50 m from woodland edges (P = 0.09). Parasitism rates were not related to distance from cropland edges, although parasitism rates ≤50 m from woodland and cropland edges were statistically similar (P = 0.16). Dickcissel nest densities were lower ≤50 m from woodland edges relative to farther distance intervals (P = 0.004), indicating dickcissel avoidance of this edge type. There was no similar pattern of nest density on cropland-edged sites, but nest densities ≤50 m from woodland and cropland edges were statistically similar (P = 0.17). Thus, some woodland edge effects on this grassland bird species were apparent but might vary geographically.