Morphological characteristics of Cape sugarbirds (Promerops cafer) from Helderberg Nature Reserve

Abstract

Cape sugarbirds (Promerops cafer) are the largest nectarivores in the Western Cape and feed almost exclusively on protea nectar and associated arthropods. Helderberg Nature Reserve, Western Cape, South Africa, has a large diversity of Protea and supports breeding sugarbirds. As part of a larger study, we captured sugarbirds using mist-nets during the breeding and non-breeding season at several sites in the Helderberg Nature Reserve, Western Cape, South Africa, from 1996 to 2000. From these data (n=283 males, 272 females), we found that in both sexes, individuals with longer tails have longer wings. Males were significantly larger in mass, culmen, head, tarsus, wing and tail length than females. Males with larger mass were larger in all morphometric  measurements than those with smaller mass. Mate choice and territory defence may be based on wing and tail ornament displays of male sugarbirds, thus larger males with larger ornaments could benefit through greater breeding success than smaller males.

Key words: sexual size dimorphism, ornament, passerine.