Abstract

Cape Sugarbirds (Promerops cafer) are southern African endemics, found in the Western and Eastern Cape provinces of South Africa, where they feed almost exclusively on the nectar of Protea inflorescences. Male sugarbirds were territorial during the breeding season, and territory size and quality, as well as breeding success were determined over two breeding seasons for a population in the Helderberg Nature Reserve in the Western Cape. In 1998 fledging success of sugarbirds was significantly greater for males defending large territories. Large territories had more inflorescences available and thus greater nectar energy. Energy availability from nectar appeared to constrain female fecundity but not fledging success. The number of inflorescences constrained fledgling success but not female fecundity in 1998. There was a greater predation rate and greater numbers of inflorescences on individual territories in 1999 than in 1998, resulting in a reduction of constraints of territory quality on breeding productivity. Cape Sugarbirds are sexually dimorphic with respect to tail length and wing ornament size, but the size of neither ornament correlated to male territory size, female fecundity or fledgling success. Female Cape Sugarbirds appear to base mate choice on the size and quality of the males' territories rather than on the size of the males' secondary sexual characteristics. Tail length and wing ornamentation of the male may play a role in territory defence and advertisement.