Impacts of cattle grazing on forest structure and raptor distribution within a neotropical protected area

Uncontrolled cattle grazing is frequent in protected areas across the tropics but its effect on habitat structure and biodiversity is poorly known. We used generalized additive models to examine the precise relationships between cattle grazing intensity, vegetation structure, and raptor occurrence and richness across 39 1-km(2) plots within the North West Biosphere Reserve, Peru. Cattle grazing was widespread and intensity was negatively correlated with average canopy height and percentage of vegetation cover at 5-15 m. Raptors were influenced by cattle density but they were probably more strongly influenced by canopy and sub-canopy characteristics. Raptor species responded differently to increasing cattle density: presence of species that hunted or searched for food in open habitats increased with cattle density, while presence of range restricted species that hunted from perches, and declining species decreased. Moderate cattle densities (20-60 cows km(-2)) may actually benefit some raptor species and help to maintain the high raptor diversity in the study area. Reserve authorities should, however, act to reduce cattle densities in some areas, which can exceed 120 cows km(-2), that seriously affect some key raptor species, and cause forest to be converted to permanent cattle pasture.