A multivariate analysis of bird species composition and abundance between crop types and seasons in southern Ontario, Canada

Many farmland bird species are declining in North America and Europe, yet t here are few data documenting bird use of agricultural landscapes, especial ly in Canada. This information is needed in order to identify candidate fac tors contributing to declines. We examined the influence of crop type and a djacent habitat on birds in fields of four crop types in three southern Ont ario counties during the 1988 breeding (May-July) and 1987 and 1988 migrati on (August-September) seasons, using canonical correspondence analysis (CCA ). Crops included apple Malus spp. orchards in Norfolk, soybeans Glycine ma x in Essex, vineyards Vitae spp. in Niagara and corn Zea mays (maize) in al l three counties. Bird assemblages differed between counties because corn i n Norfolk had more adjacent wetlands and woodlands than those in Essex. Dur ing the breeding season (1988), significant habitat variables explaining va riation in bird assemblages tin order of importance) were adjacent apple or chards, wetlands, and "other" wooded habitats and apple as the crop las dis tinct from adjacent apple orchards). During migration, apple as the crop wa s most important, followed by crop type corn (distinct from adjacent corn), adjacent wetlands and adjacent other crops in 1988. Apple as the crop was most important, followed by grape as the crop (distinct from adjacent viney ards) and wetlands in 1987. Based on median vector distances in ordination space as a measure of the difference between breeding and migration periods , bird assemblages in soybean and corn in Essex changed most, while birds a ssemblages in apple orchards changed least, although differences were not s ignificant among crops. Our results emphasize the importance of non-crop an d crop habitats for birds during both breeding and migration seasons.