Habitat relationships of diurnal raptors at local and landscape scales in southern temperate grasslands of Argentina

Abstract

We evaluated the relationship between an assemblage of diurnal raptors and local-and landscape-scale habitat variables in the eastern portion of South America's temperate grasslands in Argentina (37°32'-37°45'S, 57°19'-57°26'W). The landscape is a mosaic of agroecosystems and natural grasslands. Raptor species were sampled using fixed-distance point-counts, from October 2004 to February 2005. We used generalised additive models to analyse the relationship between raptor occurrence or abundance and environmental predictors at two spatial scales: local (at plot level) and landscape (areas of 25 and 100 km2 around the survey points). At local scales we measured vegetation height and percentage cover. Landscape-scale variables included percentage of each habitat type, landscape diversity, and fractal dimension. Higher values of species richness were recorded in landscapes with a complex matrix of disturbed and undisturbed plots. The abundance of Chimango Caracara (Milvago chimango) was positively associated with roads, sites with a complex matrix of disturbed and undisturbed plots, and high levels of forest cover. The presence of Long-winged Harrier (Circus buffoni) increased in landscapes dominated by natural habitats, mainly natural grasslands. The presence of Southern Crested Caracara (Caracara plancus) increased mostly in plots with high amounts of short grass cover and away from roads. Based on our results, we suggest that maintenance patches of natural grassland is essential for the preservation of ground-nesting species, and preservation of habitat diversity would ensure that most of the raptor species in the assemblage had their ecological requirements met.