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

Calf, Kathleen Marjorie (1999-12)

Thesis (M.Sc.)--University of Stellenbosch, 1999.

Thesis

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.

AFRIKAANSE OPSOMMING: Daar is twee spesies suikervoels, naamlik die Kaapse en Gurney se suikervoel, beide endemies tot suider Afrika. Die rol van territoriumgrootte en kwaliteit op hulle paringsukses en voorplantingsukses is vasgesteI. Verskille tussen hierdie twee spesies, wat betref manlike territoriumgrootte- en kwaliteit, reflekteer die hoer Protea spesiesdiversiteit en boomdigtheid van die Kaapse suikervoel se habitat. Beide paringsukses (die aantal eiers gelS deur die wyfie van die paar) en voorplantingsukses (die aantal suksesvolle kleintjies) van die Kaapse suikervoel was hoer as die van Gurney se suikervoeI. Dit dui aan dat die beskikbare energie in nektar en Athropoda die parings-en voortplantingsukses van Gurney se suikervoel benadeel. Geen beduidende verskille in parings- ofvoorplantingsukses is gevind tussen die twee broeiseisoene van die Kaapse suikervoel nie. Baie Kaapse suikervoels het jaarliks na hulle vorige broeiterritoria teruggekeer. Die res is moontlik deur roofdiere gevang, of het elders gegaan om hul territoriumgrootte- en kwaliteit te verbeter. Die parings- en voortplantingsukses van manlike Kaapse suikervoels was beduidend hoer vir mannetjies wat groot territoria, met 'n hoer nektar energie beskikbaarheid, verdedig het. Energie beskikbaarheid in arthropoda het nie parings- en voortplantingsukses van Kaapse suikervoels beinvloed nie, aangesien dit volop beskikbaar was. Daarenteen het die lae arthropoda energie beskikbaarheid geblyk om die voortplantingsukses van Gurney se suikervoel te benadeel, aangesien volwasse suikervoels arthropoda vir hulle kleintjies voer. Manlike suikervoels het 'n verlengde stert en 'n knop op die sesde primere vere, maar in die geval van beide spesies was daar nie 'n verband tussen ornamentlengte en parings- en voortplantingsukses nie. Stertlengte en vertonings van suikervoels mag belangrik wees vir territoriumbehoud aangesien manlike Kaapse suikervoeJs in 1999 en manlike Gurney's suikervoels met lang sterte, groter middel broeiseisoenterritoria verdedig het as mannetjies met kort sterte. Eweneens het manlike Gurney se suikervoels met langer primere veerknoppe groter territoria verdedig aan die einde van die broeiseisoen. Die verminderde seksuele dimorfisme in vlerk- en stertornamentasie by Gurney se suikervoel, mag die resultaat wees van lae voedselbeskikbaarheid, wat 6f ornamentgroei benadeel, 6fterritorialiteit, met 'n gepaardgaande afname in die belangrikheid van ornamente wat in territoriumvertonings gebruik word. Beide Kaapse en Gurney se suikervoels het meer tyd gespandeer om bloeiwyses te ondersoek vir nektar, as om te soek vir arthropoda. Daar was tussen die twee spesies beduidende verskille in die tyd spandeer aan sekere aktiwiteite gedurende verskillende tye van die dag: Gurney se suikervoel het baie meer tyd geneem om buite die territorium te voed of in borne te skuil as die Kaapse suikervoeI. Vir laasgenoemde was die tyd gespandeer om bloeiwyses te ondersoek vir nektar beduidend gekorreleerd met nektarvolume- en konsentrasie, sowel as met energie beskikbaarheid. Dit blyk dat hulle energie opbrengs maksimaliseer deur in die oggend op nektar van die bearded Protea te voed, en in die middag, wanneer nektar energie beskikbaarheid die hoogste is, op aile Proteagroepe. Daarenteen het Gurney se suikervoel ewe lank gevoed reg deur die dag. Kaapse suikervoels het meestal op die bearded Protea gevoed tydens die middel van die broeiseisoen, maar meestal op die spoonbraet Protea aan die einde van die broeiseiseon, nadat die bearded Protea reeds opgehou blom het.

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