Nesting resource availability for cavity adopter birds in a tropical dry forest of Central Mexico

Nesting resources for cavity-adopter birds commonly have spatial aggregation patterns within tropical dry forests. Spatial aggregation occurs because large trees, carrying large cavities, are restricted within small semideciduous forest areas. In contrast, deciduous forests occupy most of the coverage with smaller trees and cavities. Consequently, semideciduous forest loss could imperil cavity-adopter birds with large bodies. To test this hypothesis, we performed an intensive search in a tropical dry forest in Central-Mexico. We surveyed 5 transects -0.2 ha- in both deciduous and semideciduous forest, totalizing a survey of 2 ha. There were no differences in resource density between deciduous (4 +/- 6.51 cavities/ha) and semideciduous forest (11 +/- 6.51 cavities/ha). However, semideciduous forest cavities had wider entrances and were in larger trees. Besides, 90% of nesting resources for birds with bodies > 6 cm were restricted within the semideciduous forest, including Megascops seductus, an endemic owl, and Ara militaris, a threatened macaw. Bird-excavated cavities were associated with deciduous forest and Pachycereus weberi cacti. In contrast, decay cavities were associated with semideciduous forest and Enterolobium cyclocarpum trees. Our results suggest that the conservation of large-bodied cavity-adopter birds within dry forest depends on semideciduous forest coverage.