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Parrots have been transported and traded by humans for at least the last 2000 years and this trade continues unabated today. This transport of species has involved the majority of recognized parrot species (300+ of 382 species). Inevitably, some alien species either escape captivity or are released and may establish breeding populations in the novel area. With respect to parrots, established but alien populations are becoming common in many parts of the world. In this review, we attempt to estimate the total number of parrot species introduced into the wild in non-native areas and assess how many of these have self-sustaining breeding populations. Based the public databases GAVIA, eBird, and iNaturalist, 166 species of Psittaciformes have been introduced (seen in the wild) into 120 countries or territories outside of the native range. Of these, 60 species are naturalized, and an additional 11 species are breeding in at least one country outside of their native range (86 countries or territories total). The Rose-ringed Parakeet (Psittacula krameri) and Monk Parakeet (Myiopsitta monachus) are the most widely distributed and successful of the introduced parrots, being naturalized in 47 and 26 countries or territories, respectively. Far and away, the United States and its territories support the greatest number of naturalized parrots, with 28 different species found in either the continental US, or Hawaii or Puerto Rico. Naturalized species as well as urbanized native species of parrots are likely to continue increasing in numbers and geographical range, and detailed studies are needed to both confirm species richness in each area as well mitigate potential ecological impacts and conflicts with humans.
Preston et al. (Sun,) studied this question.