diversity Review The Number and Distribution of Introduced and Naturalized Parrots Carlos E. Calzada Preston and Stephen Pruett-Jones *   Citation: Calzada Preston, C.E.; Pruett-Jones, S. The Number and Distribution of Introduced and Naturalized Parrots. Diversity 2021, 13, 412. https://doi.org/10.3390/ d13090412 Academic Editors: Michael Wink, José L. Tella, Guillermo Blanco and Martina Carrete Received: 15 June 2021 Accepted: 26 August 2021 Published: 29 August 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Department of Ecology and Evolution, University of Chicago, 1101 East 57th St., Chicago, IL 60637, USA; carlosc@uchicago.edu * Correspondence: pruett-jones@uchicago.edu; Tel.: +1-630-248-2360 Abstract: 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. Keywords: naturalized parrots; introduced species; invasive species; world parrot trade; invasion biology 1. Introduction Parrots have been transported and traded by humans for at least the last 2000 years and this trade continues today [1]. Cardador et al. [2] summarized trade data available through the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES [3]) and documented that during the 20-year period 1975 to 2015, more than 19 million individual parrots of 336 species were legally traded among countries. This involved an average of more than half a million birds each year, with the parrot trade representing approximately 25% of all legal bird trade [2]. Inevitably, some individuals of introduced alien species either escape captivity and/or are accidentally or purposefully released and may begin breeding in the wild in the novel area [4,5]. Parrots are no exception and released or escaped parrots are often quite successful at surviving in the wild in new areas. Over time, if a successful breeding population is established, the species would be considered naturalized in that area. In some cases, the new populations can expand rapidly and grow exponentially in size [6–10]. If the species extends its naturalized range and establishes additional populations, it may become invasive. Naturalized and invasive species are increasing worldwide, and parrots represent an increasingly large proportion of the naturalized bird species [11,12]. Although the Diversity 2021, 13, 412. https://doi.org/10.3390/d13090412 https://www.mdpi.com/journal/diversity