Convergent niche shifts of endangered parrots (genus Amazona) during successful establishment in urban southern California

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 analysed 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.