Corridor use, habitat selection, and route choice by forest birds in the fragmented tropical dry forests of Costa Rica

Abstract

Tropical forests hold the majority of the world’s biodiversity, but face tremendous threats from agricultural expansion. Among these forests, dry forests have already undergone extensive clearing and only 2% of the original tropical dry forest remains in Mesoamerica. In such fragmented landscapes, the movement of individuals among subpopulations is fundamental to long term population persistence. Despite the importance of movement, little is known about how forest-dependent birds move through fragmented areas and use connecting habitat elements, like corridors. To address this deficiency, I translocated individuals of two species of forest birds with differing forest dependence in three treatments in the fragmented tropical dry forests of northwestern Costa Rica: along a riparian corridor, along a fencerow, or across pasture. I then followed their return trajectories with unprecedented resolution, recording positions approximately every 15 min for up to four days. Detailed route information yielded four main conclusions. First, riparian corridors facilitated the movement of the forest specialist barred antshrike (Thamnophilus doliatus). In riparian corridor treatments, returns to their original territories were faster and more likely, they selected forest habitat more strongly, and they traveled further from the forest edge. Second, fencerows were not sufficient corridors for the specialist, which generally chose longer routes in forest rather than more direct routes via fencerows. Third, individuals adjusted their behaviours based on habitat context. In addition to changes by the specialist in riparian corridor treatments (above), the generalist rufous-naped wren (Campylorhynchus rufinucha) selected forest more strongly in riparian corridor treatments and selected edge habitat more strongly with decreases in forest cover. Finally, the specialist chose more forested steps when they were far from their territories and when in forest habitat. They preferred steps ending in stepping stones (isolated trees) when available routes had low forest cover, but avoided them when forest cover was higher. I conclude that forested habitat and corridors benefit the movement of forest specialist birds and the conservation of these habitats will be important in this landscape and likely others. Furthermore, stepping stones may be an important element for the movement of birds through the most inhospitable matrix where forested alternatives do not exist.