The ecological basis of sensitivity of brown treecreepers to habitat fragmentation: a preliminary assessment Original Research Article

We attempted to identify the mechanisms responsible for adverse effects of habitat fragmentation on brown treecreepers (Climacteris picumnus) inhabiting eucalyptus woodland in northeastern New South Wales, Australia by comparing demography and foraging ecology of birds in highly fragmented and relatively unfragmented landscapes. In particular, we investigated three possibilities, disrupted dispersal due to patch isolation, reduced fecundity due to elevated nest predation, and reduced food availability due to habitat degradation. Nesting success was high in both highly fragmented and less fragmented habitat. Of first nests, 88% were successful, and 60% of successful groups attempted a second brood. However, there were many more groups in the more fragmented habitat than in the less fragmented habitat that lacked a female for most or all of the breeding season, and thus did not attempt nesting (64% vs 13%). In both the more fragmented and the less fragmented habitat, both males and females spent about 70% of their time foraging and 65% of their foraging time on the ground. We reject reduced fecundity in fragmented habitat as an explanation of adverse effects of habitat fragmentation on brown treecreepers. Thus sensitivity to habitat fragmentation has a different basis for this species in this landscape than that suggested for Nearctic-Neotropical migrants in eastern North America. We also reject the possibility of reduced food availability in fragmented habitat. Our data support disrupted dispersal as a likely explanation for the decline of brown treecreepers in fragmented habitat. However, we can not rule out forms of habitat degradation other than reduced food availability.