Raptors of a Neotropical City: Diversity and Habitat Relationships along an Urbanization Gradient

Urbanization involves changes in landscape terrain, hydrology, and vegetation. These changes allow some wildlife species to thrive in cities while inhibiting others. We analyzed how an urbanization gradient (i.e., percentage of impervious surface) in Xalapa, Mexico, affects raptors habitat associations and at what percentage of impervious surface these effects are the most pronounced. We also characterized the spatial distribution of species along this gradient and quantified seasonal effects. We conducted intensive area searches along an urban-to-conserved gradient inside 20, 500-m radius circular plots. Through direct observations and call-broadcast surveys, we estimated relative abundance, richness, and Shannon diversity index of diurnal and nocturnal raptors. From June 2019-February 2020, we visited each site during three seasons (breeding, fall migration, and winter), during two daily cycle periods, from 07:00-12:00 h and 19:00-00:00 h. We obtained 201 individual records of 14 species. Species abundance ranged from 1-45 individuals from 1-10 species (gradient richness), and the Shannon diversity index varied from 1-7.02 along the urban gradient. As expected, better conserved sites along the gradient held the highest diversity. Our results indicate that the transition from the intermediate to the most urbanized sites (> 70% impervious surface) is where the most abrupt filtering occurs, and we observed only four species in the most urbanized areas. According to Detrended Correspondence Analyses and two-way PERMANOVAs, the spatial distribution of the raptor community in Xalapa is significantly affected by the degree of urbanization, with some resident species using urban areas and migratory species using the intermediate and conserved areas. Our findings expand our understanding on how urbanization influences raptor communities in Neotropical cities. However, more research is needed to determine how urbanization filters raptor assemblages in cities worldwide.