Browsing by Author "Calf, Kathleen Marjorie"

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    The role of male territory size and quality in mating and reproductive success of Cape and Gurney's sugarbirds, Promerops cafer and Promerops gurneyi
    (Stellenbosch : Stellenbosch University, 1999-12) Calf, Kathleen Marjorie; Cherry, M. I.; Downs, Colleen; Stellenbosch University. Faculty of Science. Dept. of Botany & Zoology.
    ENGLISH ABSTRACT: There are two species of sugarbirds, the Cape and Gurney's sugarbirds, and both are endemic to southern Africa. The,role of territory size and quality on their mating and reproductive success was determined. Differences in male territory size and quality between Cape and Gurney's sugarbirds reflect the higher Pro tea species diversity and tree density of Cape sugarbird habitat. Both mating (the number of eggs laid by the female of the pair) and reproductive (the number of successful fledglings) success were greater for Cape sugarbirds than for Gurney's sugarbirds, indicating that nectar and arthropod energy availability constrained their mating and reproductive success. No significant differences were found in mating or reproductive success between seasons for Cape sugarbirds. Many Cape sugarbirds returned annually to their previous breeding territories; non returners may have been predated on or moved elsewhere to improve territory size and quality. Male Cape sugarbird mating and reproductive success were significantly greater for males defending large territories, with greater nectar energy availability. Sugarbird adults feed arthropods to their offspring but arthropod energy availability was abundantly available to Cape sugarbirds and did not influence their mating or reproductive success. Low arthropod energy availability, however, constrained Gurney's sugarbird reproductive success. Male sugarbirds have elongated tails and a bulge on the sixth primary feathers, but in neither case was ornament length related to mating or reproductive success in either Cape or Gurney's sugarbirds. Tail length and displays of sugar birds may be important in territory maintenance as male Cape sugarbirds in 1999 and male Gurney's sugarbirds with long tails defended larger mid breeding season territories than males with short tails. Similarly, male Gurney's sugarbirds with longer primary feather bulges defended larger territories at the end of the breeding season. The reduced sexual dimorphism in wing and tail ornamentation in Gurney's sugarbirds may be a result of low food availability either constraining ornament growth, or reduced territoriality with an associated decline in the importance of ornaments used in territorial displays. Both Cape and Gurney's sugarbirds spent more time probing inflorescences for nectar than hawking for arthropods. Within each species, there were significant differences in the amount of time spent in some activities at different times during the day - Gurney's sugarbirds spending considerably longer feeding off territory or hidden in trees than Cape sugarbirds. Time spent probing inflorescences for nectar was significantly correlated with nectar volume, concentration and energy availability for Cape sugarbirds. They appear to maximise energy gain by feeding on nectar from bearded Protea in the morning and feeding on all Pro tea groups at midday, when nectar energy availability was greatest. In contrast, Gurney's sugarbirds spent the same amount of time feeding throughout the day. Cape sugarbirds fed mostly from bearded Pro tea at mid breeding season, but from spoonbract Pro tea at the end of the breeding season, once bearded Pro tea had finished flowering.