Comparative Behaviour and Ecology of Some Australian Bark Foraging Birds

Abstract

Four species of bark-climbing birds occur in south-eastern Australia: the White-throated 'Climacteris leucophaea', Red-browed 'C. erythrops' and Brown 'C. picumnus' Treecreepers, and the Varied Sittella, 'Daphoenositta chrysoptera'. Preliminary studies of the three treecreepers showed that White-throated and Red-browed, similar in external morphology, were arboreal, while the larger Brown was semi-terrestrial. The White-throated and Red-browed were similar in foraging behaviour, but differed in social organization. The present study aimed to investigate the relationship between social organization and ecology in all of the above-mentioned bark foragers. Data were collected on all aspects of their life history, as such information was not available in the literature. The White-throated, Red-browed and sittella were studied at Wollomombi Falls, and the White-throated and Brown at Swan Vale, both sites in north-eastern New South Wales. ... Many of the differences between the White-throated Treecreeper and its congeners in life history characteristics presumably relate to ecological factors in their past. It is argued that the White-throated evolved in rainforests, where lack of suitable holes forced it to have generalized nesting sites and roost on the surface of tree-trunks. To avoid predation in the dense, dark rainforests, individuals spaced out and relied more on acoustic cues for communication. The protracted nesting cycle may have evolved to reduce activity at the nest (and thus, conspicuousness to predators), and possibly to compensate for relatively low food abundance. By contrast, the relatively open sclerophyll habitat of the Red-browed and Brown probably placed a high premium on gregariousness. Predation was particularly important to the ground foraging Brown, as evidenced by the evolution of an alarm call, distraction displays and mobbing. Food localization may have been more significant in the Red-browed, in view of their present localized distribution, specialized feeding sites, and lack of morphological adaptations for climbing compared to the White-throated. In addition, it is proposed that the relatively homogeneous bark texture of rainforest trees predisposed the White-throated, and possibly the sittella, towards stringybarks when they moved into adjacent sclerophyll forests, but it is difficult to see why these two species occupy opposite ends of the social continuum.