Frugivory and Coexistence in a Resident and a Migratory Vireo on the Yucatan Peninsula

Abstract

The White-eyed Vireo (Vireo griseus) and the Mangrove Vireo (V. pallens) are two of the most common species of insectivorous bird on the Yucatan Peninsula. Mangrove Vireo pairs maintain year-long territories primarily in scrub, whereas individual White-eyed Vireos defend territories in a broad range of terrestrial habitats. The two species show a strong reciprocal distribution along a successional gradient from regenerating pasture and old field to mature dry forest. Within second growth scrub, White-eyed Vireos are primarily associated with patches of trees. Despite minor morphological differences typical of migrant- resident comparisons, we found no significant differences in the rates of different locomotory movement, in the relative proportion of attack type used, nor in foraging substrate. The major foraging differences were a lower reduced attack rate and greater use of fruit (primarily Bursera simaruba) in the White-eyed Vireo. Playback experiments failed to draw significant interspecific responses to song playback and elicited weak responses to conspecific and heterospecific chatter calls. Simultaneous call-in experiments and opportunistic observations failed to provide evidence of interspecific aggression. White-eyed Vireos, however, consis- tently chased Mangrove Vireos out of fruiting Bursera. We hypothesize that the extensive use of Bursera fruit allows White-eyed Vireos to over-winter in mature forest on the Yucatan Peninsula, a habitat that apparently cannot support breeding by vireos in the White-eyed Vireo complex.