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Alien birds are widely distributed across the globe, but information on their environmental impacts is available for less than a quarter of the regions in which they are located. We test a series of hypotheses better to understand why impact data are available for some regions but not others. Information on factors hypothesised to influence spatial variation in the availability of impact data were collated for 60 regions with actual, recorded alien bird impacts, and 187 regions without. These data were analysed using mixed effects models. The characteristics of alien bird invasions most strongly influence the availability of impact data, which are more likely to be available for regions with higher alien bird species richness and longer alien bird residence times. There are many regions of the world that lack impact data but are characterised by high alien bird species richness and long alien bird residence times: it is likely that the impacts of alien birds are going unnoticed within them. To a lesser extent, impact data are also more likely to be available for regions characterised by higher economic development. Improving the capacity for research amongst less developed regions may therefore be a key strategy to improve our understanding of the impacts of alien birds. Impact data availability was not found to be associated with impact severity, and therefore we cannot conclude that regions lacking impact data do so because the impacts sustained within them are less severe. [ABSTRACT FROM AUTHOR]

The global trade in alien cage birds is flourishing and is considered to be one of the major routes by which species are entrained into the human-mediated invasion pathway. Here, we explore the likely influence of the wild bird trade on alien bird invasions in Taiwan. Specifically, we analyse the characteristics of alien bird species that have been successfully introduced and established at large in the wild. We use phylogenetic regression models to compare the traits of alien species recorded in the cage bird trade in Taiwan that have (or have not) subsequently been recorded at large in the wild, and the traits of species recorded in the wild that have (or have not) established (species identified in the Breeding Bird Survey in Taiwan). Alien species were more likely to be recorded as successfully introduced if they were commonly for sale in the Taiwanese pet bird trade, and possessed songs considered to be more attractive to people. Species that have been sold in the pet market for a longer period were also more likely to have been recorded in the wild. Establishment success was more likely for large-bodied bird species, but not strongly related to other predicted determinants of success, including proxies for propagule pressure and climate matching. We conclude that the pet trade influences bird invasions in Taiwan by determining which species are exposed to novel environments there, but which of those introduced species goes on to establish may depend more on their intrinsic life histories. [ABSTRACT FROM AUTHOR]