Ecological Bulletins 54: 141–156, 2013 Avian distribution along a gradient of urbanization in northeastern Puerto Rico Edgar O. Vázquez Plass and Joseph M. Wunderle Jr We studied avian distribution along an urban to forest gradient in northeastern Puerto Rico to document how dif- ferent species, species groups, and diet guilds respond to urbanization. Mean avian abundance and species richness sampled at 181 point count sites increased with urbanization and was associated with measures of developed habitat, pasture and elevation. Endemic species were sensitive to urbanization as evidenced by their negative association with an urbanization index, positive association with forest cover, and their rarity in urban habitat in contrast to their abundance and species richness in forest. Exotic species showed the opposite pattern by a positive association with an urbanization index and highest abundance and species-richness in suburban/urban habitats and absence from forest. Resident (non-endemic) species were found throughout the gradient, although species differed in the locations of peak abundance along the gradient. Resident species also displayed a positive association with the urbanization index and their abundance and species richness increased with urbanization. The increased avian abundance and species richness with urbanization was attributed to exotic granivores and omnivores and resident insectivores, granivores and omnivores. We hypothesize that availability of nearby undeveloped habitats may be critical for maintaining avian abundance and species richness in Puerto Rico’s urban areas, but emphasize that research is needed to test this hypothesis. E. O. Vázquez Plass (
[email protected]), Dept of Biology, Univ. of Puerto Rico, Río Piedras, PR 00931-3360, USA, present address: Dept of Natural Sciences, Univ.