Functional responses in habitat selection by tropical birds moving through fragmented forest.
The ability of animals to move through a landscape is a fundamental determinant of population persistence in fragmented habitats. This movement can be affected by both the composition and configuration of the remaining habitat. To date, few studies have examined the habitat selection of animals moving in novel landscapes or addressed whether animals exhibit a functional response in selection as available habitat changes. To assess habitat selection during movement, we translocated 60 individuals of two species of birds with differing forest dependency in three configuration treatments in a highly fragmented, tropical dry forest landscape: along a forested riparian corridor, along a fencerow (row of live trees) or across pasture. We closely followed the return routes of translocated birds to determine their choice of habitat and proximity to the forest edge. We then tested whether habitat composition or configuration (treatment) best explained individual variation in habitat selection. Both species preferred habitat closer to the forest edge, but this preference was weaker in the forest specialist, the barred antshrike Thamnophilus doliatus. This species selected routes in forest habitat, which included riparian corridors, over fencerow and stepping stone habitat, which were all preferred over pasture habitat. By contrast, the forest generalist, the rufous-naped wren Campylorhynchus rufinucha preferred forest equally to fencerow and stepping stone habitat over pasture habitat. For it, fencerows were selected more strongly than stepping stones. Analysis of the individual variation in selection for forest habitat revealed that both species exhibited a functional response to habitat configuration, selecting forest more strongly in riparian corridor treatments where it was also more abundant. The forest specialist also reduced its preference for edge habitat in riparian corridor treatments. Synthesis and applications. The unprecedented precision of our route information demonstrates the extent to which our forest specialist preferred to travel in forest relative to fencerow and stepping stone habitat. Functional responses to habitat configuration indicated that both species make more use of other habitats when forested corridors are not present. Stepping stones in particular may be important features to the conservation of forest birds in highly fragmented habitats.