Bill Shape and Size in Honeyeaters and other small Insectivorous Birds in Western Australia

Abstract

Highly nectarivorous honeyeaters, more insectivorous honeyeaters and non-honeyeater insectivores all showed a similar linear relationship between bill length and the cube root of body mass. Bill length increased with body mass at a faster rate in insectivorous honeyeaters than in insectivorous non- honeyeaters. In the more nectarivorous honeyeaters there was no clear relationship between bill length and either bill depth or body mass. It is suggested that mechanical considerations associated with taking large insects from surfaces restrict the length of the bill in both insectivorous non-honeyeaters and, to a lesser extent, in insectivorous honeyeaters. The longer bills of highly specialized honeyeaters may largely restrict them to small flying insects.