The role of male territory size and quality in mating and reproductive success of Cape and Gurney's sugarbirds, Promerops cafer and Promerops gurneyi

[摘要] ENGLISH ABSTRACT: There are two species of sugarbirds, the Cape and Gurney's sugarbirds, and both areendemic to southern Africa. The,role of territory size and quality on their mating andreproductive success was determined. Differences in male territory size and qualitybetween Cape and Gurney's sugarbirds reflect the higher Pro tea species diversity andtree density of Cape sugarbird habitat. Both mating (the number of eggs laid by thefemale of the pair) and reproductive (the number of successful fledglings) successwere greater for Cape sugarbirds than for Gurney's sugarbirds, indicating that nectarand arthropod energy availability constrained their mating and reproductive success.No significant differences were found in mating or reproductive success betweenseasons 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 territorysize and quality. Male Cape sugarbird mating and reproductive success weresignificantly greater for males defending large territories, with greater nectar energyavailability. Sugarbird adults feed arthropods to their offspring but arthropod energyavailability was abundantly available to Cape sugarbirds and did not influence theirmating 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 ineither Cape or Gurney's sugarbirds. Tail length and displays of sugar birds may beimportant in territory maintenance as male Cape sugarbirds in 1999 and maleGurney's sugarbirds with long tails defended larger mid breeding season territories than males with short tails. Similarly, male Gurney's sugarbirds with longer primaryfeather bulges defended larger territories at the end of the breeding season. Thereduced sexual dimorphism in wing and tail ornamentation in Gurney's sugarbirdsmay be a result of low food availability either constraining ornament growth, orreduced territoriality with an associated decline in the importance of ornaments usedin territorial displays.Both Cape and Gurney's sugarbirds spent more time probing inflorescencesfor nectar than hawking for arthropods. Within each species, there were significantdifferences in the amount of time spent in some activities at different times during theday - Gurney's sugarbirds spending considerably longer feeding off territory or hiddenin trees than Cape sugarbirds. Time spent probing inflorescences for nectar wassignificantly correlated with nectar volume, concentration and energy availability forCape sugarbirds. They appear to maximise energy gain by feeding on nectar frombearded Protea in the morning and feeding on all Pro tea groups at midday, whennectar energy availability was greatest. In contrast, Gurney's sugarbirds spent thesame amount of time feeding throughout the day. Cape sugarbirds fed mostly frombearded Pro tea at mid breeding season, but from spoonbract Pro tea at the end of thebreeding season, once bearded Pro tea had finished flowering.

[发布机构] Stellenbosch University