https://orcid.org/0000-0001-7717-2642
ABSTRACT
The ranges of many raptor populations are changing, presumably in response to direct and indirect anthropogenic effects on their habitats. Anecdotal evidence suggests shifts in the distributions of Crested Caracaras (Caracara plancus; hereafter caracaras) over time across their range in the United States (USA), yet formal analysis is lacking. Here we used 30 yr of National Audubon Society Christmas Bird Count and US Geological Survey Breeding Bird Survey data partitioned into ten consecutive 3-yr time periods to assess range shifts and expansions for caracara populations in Arizona, Texas, and Florida, USA, from 1992 through 2021. Data were insufficient to evaluate the Arizona population. In contrast, observations of caracaras increased over time in Texas where the range centroid moved 72.6 km north-northeast with the population expanding into Louisiana. Observations of caracaras also increased over time in Florida, where the range centroid moved 34.3 km southwest. We suggest five competing nonexclusive hypotheses for these changes: (1) temperature increases due to climate change may have allowed expanded breeding in North America of this primarily South American species, (2) increased abundance and use of anthropogenic nesting substrates may have allowed caracara populations to expand, (3) increased foraging opportunities associated with anthropogenic landscape changes may have released otherwise constrained caracara populations, (4) reduced persecution may have allowed this behaviorally plastic species to coexist in proximity to human populations, and (5) habitat saturation may have forced increased dispersal. Future research is needed to evaluate and compare these hypotheses.