Non-random patterns and temporal trends (1912-2012) in the transport, introduction and establishment of exotic birds in Spain and Portugal

Aim Invasion processes are probably better understood for birds than for any other taxon, thanks to detailed information available on deliberate introductions performed by Europeans when they colonized other continents. Little is known, however, about current avian introductions in developed countries, including Europe. Using an unprecedented dataset on exotic birds, we assessed the sources and magnitude of recent avian introductions and characterized the transitions between main invasion stages (transport, introduction and establishment) and their temporal evolution. Location Spain and Portugal. Methods We compiled records of species introduced between 1912 and 2012, including information on transport and introduction pathways. We assessed non-randomness in the phylogenetic relationships and the biogeographic origin of species crossing each invasion stage and evaluated temporal changes in introduction patterns. Results At least 1026 exotic species have been transported to Spain and Portugal (ca. 10% of the world's birds) during the last 100 years. Of these, 377 (37%) have been recorded as introduced into the wild, of which up to 32 (9%) species have established breeding populations. Exotic species entered the invasion pathway mostly through the accidental escape of internationally traded birds, and temporal changes in introduction rates mirrored changes in the number of imported birds. The subsets of taxa successfully passing through the different invasion stages were non-random with respect to their biogeographic origin and were phylogenetically clustered in several distantly related clades. Main conclusions Our findings show that the magnitude of transport, introduction and establishment of exotic birds is much greater than usually described at a regional level, and support the hypothesis that most species fail to transit the different steps of the invasion process (the so-called tens rule). The temporal changes in introduction rates are broadly consistent with the recent global rise of accidental introductions associated with the wildlife trade.