Temporal patterns of bird abundance in cornfield edges during the breedingseason

Bird abundance in cornfield edges in Iowa was documented from mid-April thr ough early August 1992. During this period the barren, sparsely vegetated f ields are transformed into fields with dense plant cover; the availability of food resources (corn and arthropods ) also changes. Temporal patterns of bird abundance in cornfield edges differed greatly among species-some were present in cornfield edges throughout most, if not all, of the study perio d (e.g., American robin and eastern kingbird),whereas others restricted the ir use to brief periods. Some were more abundant early in the season (e.g., killdeer and horned lark); others were more abundant later (e.g., black-ca pped chickadee and indigo bunting). Much of rile seasonal change in bird ab undance in cornfield edges was attributed to tile habitat affinities of the various species and to seasonal shifts in available food resources. Birds that feed on the ground or in low herbaceous vegetation became less abundan t later in the season, whereas species that characteristically feed in shru bs or the lower canopy of trees became more numerous. The availability of w aste corn on tile soil surface, the phenology) of the developing crop and t he life history stages of major corn insect pests all contribute to the tem poral dynamics of bird abundance in cornfields. Also, seasonal patterns of bird abundance in cornfields influence avian risk of exposure to agricultur al pesticides. Effective management and conservation of avian communities a ssociated with cornfields require understanding temporal patterns of bird a bundance and their implications.