Habitat selection in two Australasian treecreepers: what cues should they use?

Abstract

When habitats differ in quality, individuals may attempt to maximise fitness through habitat selection. However, complete tests of habitat selection are rare, in part because many studies fail to quantify fitness consequences of habitat choice. We studied habitat selection of Australasian treecreepers (Passeriformes: Climacteridae) in temperate eucalypt woodland by examining the influence of habitat characteristics and confounding factors on annual reproductive success. In the pair-breeding White-throated Treecreeper (Cormobates leucophaeus), older females and territories with fewer stumps and less woody debris produced more young, possibly because these habitat characteristics lead to reduced conflict with Brown Treecreepers (Climacteris picumnus). In the cooperatively breeding Brown Treecreeper, larger groups and territories with lower densities of shrub, moderate levels of ground cover, and greater amounts of foraging substrate produced more fledglings, whereas territories with greater invertebrate biomass produced more independent young. Predicted annual reproductive success in the best territory was up to two offspring more than predicted success in the worst territory; thus, treecreepers would benefit from selecting good quality habitat. However, complete tests of habitat selection need to evaluate whether dispersers actively sample multiple habitats and choose the best available, and thus whether individual-level processes determine large-scale patterns of distribution and abundance. These results also suggest that current conservation efforts to exclude grazing from remnant patches of eucalypt woodland may be inappropriate if not used in conjunction with other management actions, because such exclusion may dramatically increase shrub density and ground cover. Alternative management tools need to be investigated that will maintain a mosaic of microhabitat types and thus protect the eucalypt woodland ecosystem, not just a few of its species.