Morphological over-dispersion in game birds (Aves: Galliformes) successfully introduced to New Zealand was not caused by interspecific competition

A pattern of significant morphological over-dispersion among successfully introduced bird species has previously been documented on several islands. In a recent paper, Moulton et al. also document this pattern for game birds introduced to New Zealand and, in line with previous studies, infer that competition among morphologically similar species played an important role in determining the outcome of these introductions. Here, we show that competition among morphologically similar species could not have been responsible for the failure of most game bird introductions to New Zealand because most species were released at widely separated locations or at different times, did not spread and rapidly became extinct if they failed to establish, and would never have encountered other morphologically similar introduced game birds. Even when morphologically similar species were released in the same district at the same time, historical records suggest that it is unlikely that two species were ever released at precisely the same location and, even if they were, competition is an unlikely cause of introduction failures because most species were present in extremely low numbers. Our results imply that factors other than competition can generate patterns of significant morphological over-dispersion in introduced avifaunas. We show that greater introduction effort expended on more morphologically distinct species could account for over-dispersion in game birds introduced to New Zealand.