FRUGIVORY AND COEXISTENCE IN A RESIDENT AND A MIGRATORY VIREO ON THE YUCATAN PENINSULA

The White-eyed Vireo (Vireo griseus) and the Mangrove Vireo (V. pallen s) are two of the most common species of insectivorous bird on the Yuc atan Peninsula. Mangrove Vireo pairs maintain year-long territories pr imarily in scrub, whereas individual White-eyed Vireos defend territor ies in a broad range of terrestrial habitats. The two species show a s trong reciprocal distribution along a successional gradient from regen erating pasture and old field to mature dry forest. Within second grow th scrub, White-eyed Vireos are primarily associated with patches of t rees. Despite minor morphological differences typical of migrant-resid ent comparisons, we found no significant differences in the rates of d ifferent locomotory movement, in the relative proportion of attack typ e used, nor in foraging substrate. The major foraging differences were a lower reduced attack rate and greater use of fruit (primarily Burse ra simaruba) in the White-eyed Vireo. Playback experiments failed to d raw significant interspecific responses to song playback and elicited weak responses to conspecific and heterospecific chatter calls. Simult aneous call-in experiments and opportunistic observations failed to pr ovide evidence of interspecific aggression. White-eyed Vireos, however , consistently chased Mangrove Vireos out of fruiting Bursera. We hypo thesize that the extensive use of Bursera fruit allows White-eyed Vire os to over-winter in mature forest on the Yucatan Peninsula, a habitat that apparently cannot support breeding by vireos in the White-eyed V ireo complex.