Lessons from the establishment of exotic species: a meta-analytical case study using birds

1. The establishment of species outside their natural geographical ranges is an important driver of changes in global biodiversity. This creates an imperative to understand why some species are more successful than others at establishing viable populations following introduction. 2. Historical data are particularly useful in this regard, and those for birds especially comprehensive. This has resulted in the publication of regional-scale studies that have used these data to attempt to quantify relationships between establishment success and characteristics of bird introductions. 3. We use a meta-analytical approach to summarize quantitatively the results of these studies, and to assess the influence of variables invoked to explain the variation in establishment success in birds. 4. We find that variables describing characteristics specific to the individual introduction event (i.e. event-level variables), such as introduction effort (or 'propagule pressure'), are the most consistent predictors of establishment success.