Local extinctions in flocking birds in Amazonian forest fragments

Abstract

Questions: Does the tendency to join flocks predispose a bird species to local or global extinction? Does the ability to revise particular social preferences in fragmented landscapes confer greater persistence? Do solitary species of birds persist longer in small forest patches? Background: Social carnivores range more widely than solitary carnivores and are more prone to local extinction in fragmented landscapes. Flocking bird species typically range over larger areas than solitary ones, thus potentially encountering threats in and beyond the edges of their habitat more often than solitary species. Data: A 14-year bird-capture database from the Biological Dynamics of Forest Fragments Project (BDFFP) near Manaus, Brazil. Methods: From the literature, from independent field observations and mist-net captures we identified 30 species that join mixed flocks or follow ant swarms. We quantify the tendency for these species to flock both before and after habitat fragmentation. We test the effect of flocking on understory species' persistence in forest fragments of 1, 10 and 100 ha. Results: Species that typically forage in flocks before plot isolation persist for shorter times than those that infrequently join flocks. Species that drop out of flocks after fragmentation persist longer than those that remain in flocks. Our model outperformed a nested analysis of variance that treated each species as a variable, inherently testing for life-history idiosyncrasies and phylogeny. Recapture rates, calculated using MARK, did not explain the residual variation from our model. Flocking behaviour, and its plasticity, influence species persistence and so are important criteria in understanding local extinction. © 2006 Stuart L. Pimm.