Masters Thesis

Habitat use of Nearctic-Neotropic migrant birds in northeastern Costa Rica

Many birds replenish energy reserves during semiannual migratory stopover periods in northeastern Costa Rica. Despite the importance of tropical staging areas to migrants, little research has focused on tropical stopover ecology. In this study, habitat use of 11 fall migrant species in northeastern Costa Rica were examined using bird banding data in association with a priori modeling methodologies. Frugivore capture rate and ripening of fruit peaked correspondingly in mid-October indicating a potential relationship between migrant arrival and the timing of ripe fruit availability. Top migrant habitat use models (encompassing a cumulative 95% AICc weight) contained fruit or arthropod abundance for 73% of the study species. Only Canada Warbler, Mourning Warbler and Eastern Wood-pewee, all insectivores, had top models that emphasized vegetative attributes without resource variables. Model results suggest that frugivorious migrants used fruit and insectivorous migrants used structure as cues for habitat use. Insectivores may have used habitat structure as a cue because of inherent difficulties associated with directly assessing arthropod availability.

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