Avian cross-habitat spillover as a bidirectional process modulated by matrix type, forest cover and fragment size

Abstract

Cross-habitat spillover (i.e. the movement of individuals between different habitat types) occurs very often in agricultural landscapes, following temporary crop resource pulses that work as complementary resources for biodiversity. We tested how avian spillover at edges of forest fragments is affected by the adjacent agricultural matrix contrast (sun coffee plantations or pastures), forest fragment size, and forest cover at the landscape scale. We performed paired mist netting at forest edges (forest/sun coffee plantations and forest/pastures; N = 24) and estimated the spillover ratio and the dissimilarity of birds moving in- and out- forest fragments. We found that avian spillover in highly fragmented landscapes is a bidirectional process regardless of species habitat association or feeding guild. Matrix type is a key driver of spillover, and most spillover occurred when the matrix is of less contrast (i.e. sun coffee plantations). Spillover ratio at coffee interfaces increased with forest cover and also with fragment size, meanwhile at pasture interfaces spillover only increased at high values of forest cover and fragment size. Finally, we found that the dissimilarity between bird species entering and leaving the fragments was higher in pasture matrices, while at coffee interfaces the dissimilarity was lower. Landscape management aimed at reducing the contrast between matrix and habitat, increasing habitat cover and maintaining large fragments can intensify spillover movements across natural and anthropogenic habitats, and potentially, promote more ecosystem service provision by those species that are performing spillover movements.