Agroecology of birds in organic and nonorganic farmland

Ecological relationships between wildlife conservation and farm management provide common ground for the enhancement of bird habitat and the natural suppression of pests on farmland. We compared bird populations in 15 paired organic and nonorganic sites ( cornfields plus edges, 30 sites total) that were similar in environment and edge habitat but that differed in use of fertilizers, herbicides, cultivation, and crop rotations. At each site, we used one strip transect to sample birds and vegetation in the bordering edge and cornfield perimeter (0-25 m from the edge) and another to sample in the cornfield (50-150 m from the edge). During the 1995 and 1996 growing seasons, we recorded 54 bird species, 51 in organic and 39 in nonorganic sites. On average, bird abundance on organic sites was 2.6 times higher than on nonorganic sites, and mean species richness per visit was 2.0 times greater. When analyzed separately, organic edge, perimeter, and field transects supported higher bird abundance and greater richness than did their nonorganic counterparts. Abundance and richness were higher on organic sites for insectivores, omnivores, and granivores, and for each of three migratory groups. Twelve species were individually more abundant on organic sites, and one regularly observed species was observed only on organic sites. No species had greater abundance on nonorganic sites. More non-crop vegetation on organic cornfields, most likely a result of no herbicide use, may have provided better foraging opportunities for birds. The plant food, cover, and invertebrate prey in organic cornfields appeared to augment birds not only in the field but also in the uncropped edges. Organic fields appear to benefit birds, but reproductive success needs further study. Modifying farm-management practices, especially near field edges where bird activity is concentrated, may enhance the conservation of birds and their potential predation on crop pests.