MIGRATING TO THE CITY: RESPONSES OF NEOTROPICAL MIGRANT BIRD COMMUNITIES TO URBANIZATION

Birds that migrate to the neotropics have experienced dramatic population decreases over the last few decades. Although the transformation of their wintering habitats has been related to such decreases, several neotropical migrants are tolerant of human disturbances and winter in human-altered habitat. We surveyed a neotropical city broadly to evaluate how migrant birds respond to urbanization, finding that urbanization has a negative effect on communities of migrant birds: species richness and density of migrants decreased with urbanization. Although we recorded a significant decrease in the total number of individual neotropical migrants toward the center of the city, we found no differences among species when we assessed possible effects of the distance from the city's edge by species. Only tree cover had a positive significant relationship with both species richness and bird abundance. Our results show that urbanization can have an even greater negative effect on communities of neotropical migrant birds than for those of resident birds. However, some migrants that used the urban habitats we studied are of conservation concern, indicating that urbanization can act as a two-edged sword, affecting several migratory species negatively while offering winter habitats to others.