Aim: Introduced species offer insight on whether and how organisms can shift their ecological niches during translocation. The genus Amazona offers a clear test case, where sister species Red-crowned (A. viridigenalis) and Lilac-crowned Parrots (A. finschi) have established breeding populations in southern California following introduction via the pet trade from Mexico where they do not coexist. After establishment in the 1980s, introduced population sizes have increased, with mixed species flocks found throughout urban Los Angeles. Here, we investigate the differences between the environmental conditions of the native and introduced ranges of these now co-occurring species.

Location: Southern California and Mexico.

Methods: Using environmental data on climate and habitat from their native and introduced ranges, we tested whether Red-crowned and Lilac-crowned Parrots have divergent realized niches between their native ranges, and whether each species has significantly shifted its realized niche to inhabit urban southern California. We also analyzed data from Texas and Florida introductions of Red-crowned Parrots for comparative analysis.

Results: There are significant differences in the native-range niches of both parrot species, but a convergence into a novel, shared environmental niche into urban southern California, characterized by colder temperatures, less tree cover, and lower rainfall. Texas and Florida Red-crowned Parrots also show evidence for niche shifts with varying levels of niche conservatism through the establishment of somewhat different realized niches.

Main Conclusions: Despite significant niche shifts, introduced parrots are thriving, suggesting a broad fundamental niche and an ability to exploit urban resources. Unique niche shifts in different U.S. introductions indicate that Amazona parrots can adapt to diverse environmental conditions, with cities offering a resource niche and the timing of introduction playing a crucial role. Cities can potentially serve as refugia for threatened parrot species, but the risk of hybridization between species emphasizes the need for ongoing monitoring and genetic investigations.

Observations for the Amazona parrots in southern California were collected on iNaturalist through the Free-Flying Los Angeles Parrot Project (FLAPP). Individual parrots were scored based on morphological features to confirm species identification. Only research-grade observations were included in our analysis, which was determined by two agreeing independent scorings of species identification. Observations for Amazona parrots in their separate native ranges of Mexico were downloaded from the eBird database, with filtering done to remove any observations found in introduced areas surrounding their native ranges. Red-crowned Parrot data for Texas and Florida was downloaded from eBird as well and filtered to only include observations with media for species identification. Buffers were created for each population to create randomly generated background points. Environmental data was downloaded from various online databases including Bioclim, MODIS data, and global scatterometer data. The environmental data was then pulled for each parrot (and randomly generated background points) for environmental comparison.

All data were processed using R 4.2.1