Conservation Implications Of A Limited Avian Cross-Habitat Spillover In Pasture Lands

Increasing evidence demonstrates a role for the cross-habitat spillover process in the maintenance of biodiversity in managed agricultural landscapes. However, the mechanisms that drive this process are less well understood. In particular, it is critical to know how landscape structure modulates spillover movements, and whether species are moving through the matrix to acquire resources or simply to disperse between habitat fragments. We tested landscape effects and food resource use within cattle pasture matrices. We used mist-nets to collect data on avian communities across 51 sampling sites, spanning a forest cover gradient. We additionally integrated stable isotopic analysis (delta C-13 signature) to determine the provenance of resources used (either forest - dominated by C-3 plants; or pasture, dominated by C-4). Bird movement across pasture matrices was extremely reduced, and bird occupation was concentrated near forest edges. There was a clear distinction of resource use according to species' habitat preferences, with forest-species foraging predominantly in-forests, open-area species in pastures, and generalist species having more varied diets, but still relying on a large proportion of C-3 sources. Forest cover was unrelated to avian spillover from forests into pastures, but positively related to C-3 signatures for both forest and open-area associated species. Finally, we found that most birds moving from forests to pastures were habitat generalists (63%), and that pastures work as a barrier for forest-associated species movement. Landscapes dominated by pasture are very unfavorable to the conservation of forest species, but potentially can maintain ecosystem services from the spillover of generalist species.