Effects of remnant size and connectivity on the response of Brown Treecreepers to habitat fragmentation

We studied approximately 50 groups of the cooperatively breeding Brown Treecreeper ('Climacteris picumnus') in connected and unconnected (isolated) woodland remnants in the New England Tablelands of north-eastern New South Wales during 1996-98. Large and small, unconnected remnants were more likely to contain territories lacking females than were connected habitat remnants. Using General Linear Mixed Models to control for the non-independence of groups studied in the same remnants, we found that neither remnant size nor connectivity affected nest success rate, brood size, or fledgling production. Survival of females was lower in small remnants and greatest in large, unconnected remnants. Lower survival in small remnants suggests area-sensitivity, but this effect cannot explain patterns in recruitment of females because there was no shortage of females in small, connected remnants. We conclude that remnant connectivity influences dispersal success of Brown Treecreepers, with dispersal being disrupted when remnants are unconnected. Therefore, isolation-sensitivity, not area-sensitivity, is the primary basis of the species' sensitivity to habitat fragmentation.