Plasticity and Stereotypy in Avian Foraging during Secondary Succession in Temperate Forests

Abstract

Some bird species cannot persist during early secondary succession after natural or anthropogenic disturbance of Australian Mountain Ash (Eucalyptus regnans) forest, whilst others remain abundant throughout regeneration. To conserve bird species diversity optimally in such forests, we need to know, inter alia, exactly why the latter species can persist after disturbance. Using a chronosequence approach, we documented four facets of foraging in a suite of these persistent species effectively covering 100 years of succession in E. regnans forest disturbed by wildfire or timber harvesting, namely the foraging strata, locations, substrates and behaviours used. Most species showed plasticity in their use of foraging strata and locations during succession, but four exhibited some limited stereotypy in these facets. In contrast, use of foraging substrates and behaviours was largely invariant within species during secondary succession. We suggest that switching foraging strata and locations was probably critical to persistence of most of these bird species during secondary succession, given the marked variation in structural and floristic variables that characterises this regeneration process. Some plasticity in foraging behaviour repertoire and substrate use was probably possible, but not beneficial. Although some resident bird species’ populations were severely reduced by disturbance in these forests, a substantial subset of species was sufficiently flexible in choosing foraging microhabitats to persist throughout secondary succession at pre-disturbance abundances.