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.
