Distribution of Overwintering Nearctic Migrants in the Yucatan Peninsula, I: General Patterns of Occurrence'

Point counts and mist-net surveys were employed to study the winter distri­ bution of nearctic migratory landbirds in Mexico’s Yucatan Peninsula. Overwintering mi­ grants comprised 42 regularly occurring species, and accounted for 30-58% (mean = 41%) of the individual birds encountered in surveys of a wide range of natural and disturbed habitats. Some migratory species were encountered most frequently in pastures, agricultural fields, or brushy second growth, but the main habitat for many migrants was tropical forest. Migratory and resident species showed similar degrees of specialization with respect to the successional maturity of their habitats, but residents were more likely to specialize on particular types of mature forest. After mist-net capture data were standardized by rarefac­ tion, there were no statistically significant differences in the ratio of migrants to permanent residents in habitats that ranged from pasture, through brushy old fields, to mature semiever­ green forest. For any given number of captures, species richness of both migrants and residents was substantially higher in mist-net samples from pastures and brushy old fields than in those from mature semievergreen forest. With few exceptions, nearctic migratory species that breed in mature temperate-zone forest occurred both in forest and in brushy second growth during winter, although some species were substantially less frequent in the latter habitat. In contrast, overwintering migrants that breed in edge or field habitats tended to avoid tropical forest in the Yucatan.