The effects of habitat heterogeneity on avian density and richness in soybean fields in Entre Ríos, Argentina

Abstract

Birds play several roles in agricultural lands and respond to habitat heterogeneity within the agricultural landscape. Agricultural intensification in Argentina has increased the sown area, mainly with soybean, fragmenting landscapes in the pampas and mesopotamic region. In Entre Ríos Province, the original Espinal forest has been fragmented, leaving remnant patches of natural vegetation, in cases modified by cattle grazing. These changes represent a potential threat for avian conservation. In Entre Ríos, terraces may be a useful habitat in maintaining avian diversity, similar to other non-cropped linear habitats in agricultural landscapes. We tested the hypothesis that habitat heterogeneity created by terraces would maintain higher species richness and densities of avian species that use original or modified forests within cropped areas compared to fields without terraces. The study was carried out in soybean fields with an adjacent forest and either herbaceous, shrub or no terraces in two periods (March-April 2004). Birds were surveyed using line transects in field interior and edge, and observations were carried out in one forest remnant adjoining each field. Most bird species recorded in soybean fields were insectivorous or consume invertebrates during the breeding season. Species richness, total bird density and the density of granivores, insectivores and omnivores were higher in fields with terraces than in fields without terraces. Moreover, shrub terraces had higher effect on species richness and bird density than herbaceous terraces. Our results suggest that terraces may serve as a possible tool for maintaining avian diversity in agroecosystems in Entre Ríos.