Wing Shape in Insectivorous Passerines Inhabiting New Guinea and Australian Rain Forests and Eucalypt Forest/Eucalypt Woodlands

Abstract

AssTAcr.-Based on museum skins of 47 bird species in 17 genera, I evaluated the suppositions for members of various taxonomic groups in New Guinea and Australian rain forest compared to open eucalypt forest/eucalypt woodland that in rain forest birds compared to eucalypt forest/eucalypt woodland counterparts in each group: (1) outer primary 9 tends to be proportionately shorter; (2) secondary 1 is proportionally longer; and (3) the longest primary is more proximally placed relative to the body in its series. The postulations are largely confirmed. The results are presaged by the findings of earlier writers that species operating in confined spaces should have broad wings with rounded tips, with low wing loading conferring high manoeuvrability, and that distance flyers should have wings with long wingspans and pointed tips for economy of effort. Received 1 April 1993, accepted 4 September 1994. WHEN MEASURING SKINS of New Guinea and Australian tropical rain-forest insectivorous passerines, and eucalypt forest/woodland counterparts, I found regularly occurring differences in wing form. The former tended to have more rounded wings, with the outer primary 9 relatively short, while the longest primary in the series was placed more proximally than the others in its series relative to the body in the rain-forest species. Examples were found in foliage-gleaning warblers (Gerygone), whistlers (Pachycephala), ground-feeding robins, and several other groups, suggesting that a general habitat adaptation was operating, as has been shown for several body structures by Winkler and Leisler (1992). In this paper, I quantitatively explored this observation and postulated connection in a diverse set of ecomorphological types of birds. An early paper by Savile (1957) documented the occurrence of two alternative wing types in small birds-elliptical wings found in birds that lived in confined spaces, and wings characteristic of species that remain in the air for long periods. In the former group the wing is curved to increase negative pressure and, hence, lift above, with slotting of the tips serving to minimize turbulence and ensure uniform pressure over the entire surface. The result is high lift, as well as good control and manoeuvrability. By contrast, the high-speed wing has a lower camber, a slender tapering tip, a sweepback of the leading edge, and a short chord. These features reduce drag and conserve power.