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Thesis (MSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: The uropygial gland of most birds produces a variety of hydrocarbons, lipids, waxes, fatty acids, alcohols and other organic compounds. These compounds have two widely recognized functions, viz. they are considered essential for the maintenance of a good plumage condition, and may be used for fungicidal, bactericidal or other hygienic purposes. Scimitar-billed woodhoopoes, Rhinopomastus cyanomelas, are groupterritorial birds that live in groups comprising between two and twelve individuals. Individuals enter the roost cavities shortly after sunset and exit the following morning soon after sunrise. During the period that the birds are inside the roost, they are vulnerable to a range of vertebrate predators, including snakes, genets and rats. When disturbed while roosting, woodhoopoes immediately face away from the threat hence presenting their uropygial glands in the direction of the threat. Typically, a drop of brown, highly pungent secretion is then formed at the tip of the papilla to the uropygial gland, and kept in place by a few tuft-like feathers. This response pattern has led some observers to believe that the secretion serves an anti-predatory role. It has been found that the synthetic volatile constituents of the uropygial secretion of the green woodhoopoe, P. purpureus, individually or as a mixture, have potent defensive properties against feline and reptilian predators. In addition, the compounds also showed activity against a range of bacteria. The aim of the present study was to determine the chemical composition of the uropygial secretion of the scimitar-billed woodhoopoe, Rhinopomastus cyanomelas, as a first step towards the evaluation of, inter alia, the semiochemical function of the secretion. Using gas chromatography-mass spectrometry, 179 constituents of the uropygial secretion of the scimitar-billed woodhoopoe have been identified. The majority of the constituents of the secretion are branched and unbranched aldehydes (aliphatic and aromatic), acids (aliphatic and aromatic), sulfides and ketones. This group of volatile compounds is responsible for the obnoxious odour of the secretion and possibly also for its defensive action against predators. The secretion also contains a large number of branched and unbranched alkanes and wax esters. The chemical composition of the secretion was compared with the secretion of P. purpureus as well as with that of the hoopoe, Upupa africana. The uropygial gland secretion of the scimitar-billed woodhoopoe is quite similar to that of the green woodhoopoe, although it is much more complex than that of the green woodhoopoe. In contrast to the uropygial secretions of the green and the scimitar-billed woodhoopoes, the secretion of Upupa africana does not have a strongly obnoxious odour and it also does not contain large quantities of alkanes and wax esters. / AFRIKAANSE OPSOMMING: Die uropigiale klier van die meeste voëls produseer 'n verskeidenheid van koolwaterstowwe, lipiede, was-esters, vetsure, alkohole en ander organiese verbindings. Hierdie verbindings het twee algemeen erkende funksies, naamlik die instandhouding van die goeie kondisie van die vere, en 'n swam- en kiemdodende werking. Swartbekkakelaars (Engels: scimitar-billed woodhoopoes ), Rhinopomastus cyanomelas, is groep-territoriale voëls wat in groepe van tussen twee en twaalf saam woon. Individue gaan hul neste net na sononder binne en verlaat dit weer die volgende oggend net na sonsopkoms. Terwyl die voëls binne die neste is, is hulle kwesbaar ten opsigte van aanval deur verskeie gewerwelde roofdiere, insluitende slange, muskeljaatkatte en rotte. Wanneer hulle in hul neste gesteur word, sal kakelaars onmiddellik wegdraai van die bedreiging sodat die uropigiale klier in die rigting van die bedreiging gekeer is. 'n Druppel bruin, uiters onwelriekende afskeiding vorm dan by die punt van die papil na die uropigiale klier, en word in posisie gehou deur 'n verekwassie. Hierdie gedragspatroon het aanleiding gegee tot die gedagte by sommige waarnemers dat die afskeiding as afweerstof teen roofdiere dien. Daar is gevind dat die sintetiese vlugtige komponente van die uropigiale afskeiding van die groenkakelaar, P. purpureus, individueel of as 'n mengsel, sterk afweer-eienskappe teen katte en reptiele toon. Daarbenewens het die verbindings ook aktiwiteit getoon teen 'n reeks van bakterieë. Die doel van die huidige studie was om die chemiese samestelling van die uropigiale afskeiding van die swartbekkakelaar, Rhinopomastus cyanomelas, te bepaal as 'n eerste stap met die oog op die evaluering van, onder andere, die semiochemiese funksie van die afskeiding. Deur van gaschromatografie-massaspektrometrie gebruik te maak, is 179 komponente van die uropigiale afskeiding van die swartbekkakelaar geïdentifiseer. Die meeste van die komponente is vertakte en onvertakte aldehiede (alifaties en aromaties), sure (alifaties en aromaties), sulfiede en ketone. Hierdie groep vlugtige verbindings is verantwoordelik vir die afstootlike reuk van die afskeiding en waarskynlik ook vir sy afweer-aksie teen roofdiere. Die afskeiding bevat ook 'n groot aantal vertakte en onvertakte alkane en wasesters. Die chemiese samestelling van die afskeiding is vergelyk met die van P. purpureus sowel as dié van die hoepoe, Upupa africana. Die uropigiale klierafskeiding van die swartbekkakelaar stem tot 'n groot mate ooreen met dié van die groenkakelaar, alhoewel dit veel meer kompleks is as dié van die groenkakelaar. In teenstelling met die uropigiale afskeidings van die groen- en die swartbekkakelaars, het die afskeiding van Upupa africana nie 'n afstootlike reuk nie en bevat dit ook nie groot hoeveelhede alkane en was-esters nie.