Behavioural flexibility predicts invasion success in birds introduced to New Zealand

A fundamental question in ecology is whether there are evolutionary charact eristics of species that make some better than others at invading new commu nities. In birds, nesting habits, sexually selected traits, migration, clut ch size and body mass have been suggested as important variables, but behav ioural flexibility is another obvious trait that has received little attent ion. Behavioural flexibility allows animals to respond more rapidly to envi ronmental changes and can therefore be advantageous when invading novel hab itats. Behavioural flexibility is linked to relative brain size and, for fo raging, has been operationalised as the number of innovations per taxon rep orted in the short note sections of ornithology journals. Here, we use data on avian species introduced to New Zealand and rest the link between foreb rain size, feeding innovation frequency and invasion success. Relative brai n size was, as expected, a significant predictor of introduction success, a fter removing the effect of introduction effort. Species with relatively la rger brains tended to be better invaders than species with smaller ones. In troduction effort, migratory strategy and mode of juvenile development were also significant in the models. Pair-wise comparisons of closely related s pecies indicate that successful invaders also showed a higher frequency of foraging innovations in their region of origin. This study provides the fir st evidence in vertebrates of a general set of traits, behavioural flexibil ity, that can potentially favour invasion success.