Introduction

Is an organism that spends only five to ten days a year exhibiting a certain type of behaviour likely to possess anatomy specialised to perform it? The key feature that has allowed birds to be such notable builders is a bodkin beak on a mobile neck close to a pair of sharp eyes. Nevertheless, evidence that the morphology of the beak or any other part of the bird is determined to any degree by building technique is weak or absent. The partial fusion of the front three toes of kingfishers (Alcedinidae) may assist with burrow excavation (Sick 1993), but such claims of morphological adaptations for nest building are hard to find.

Feeding is, day to day and year round, what beaks are used for, so this is likely to be the dominant influence on beak shape. Evidence to support this, although not always compiled in a systematic way, is very generally evident. Such a relationship has been deduced, for example, from the markedly different beak shapes of the Hawaiian honeycreepers (Drepanidini, Fringillidae) accompanying their radiation into different feeding specialisations (Buhler 1981, Fig. 4.1). The nests of the honeycreepers, however, are unremarkable cupshaped structures, lacking in diversity. The sturdy-billed palila (Loxioides bailleui) and Laysan finch (Telespiza cantans), birds of around 35 g (Dunning 1993), build with fine woody stems, rootlets and grasses, whereas the finer-beaked species, the apapane (Himatione sanguinea) and iiwi (Vestiaria coccinea), birds of 25 g, build with almost identical materials (Carlquist 1980).