Influence of landscape composition on bird use of rowcrop fields

We evaluated the influence of landscape composition on bird use of rowcrop (corn and soybean) fields in 6 watersheds in Iowa from mid-May to late July 1993 and 1994. We counted birds within 50-m-radius circular plots positioned randomly within rowcrop fields and determined coverages for 21 habitats within 800-m-radius circles centered on each bird census plot. We evaluated the relationships between bird abundances in rowcrop fields and the habitat coverages in the landscape by using 2 multivariate procedures. We derived 3 landscape scenarios from a cluster analysis of the original habitat variables; the abundances of 7 bird species different significantly among the 3 scenarios. Species abundances in rowcrop fields were greater in landscapes with more grassland block-cover and/or more wooded block-cover and strip-cover. Principal component analysis illustrated the responses of bird species to landscape composition: species responses depended upon the relative use (ranging from resident to occasional) that the birds made of the lowcrop fields. Habitat selection and use in birds is a multiscale phenomenon, and the landscape context should be considered when evaluating bird use of rowcrops.