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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Observations on the coexistence of Palearctic and African Orioles Oriolus spec. in Zimbabwe
Auteurs :	Sabine Baumann, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (122(2) 2001)
Article en page(s) :	67-79
Résumé :	In broadleaved deciduous woodlands of Zimbabwe wintering Eurasian Golden Oriole Oriolus oriolus are found syntopically with breeding African Golden Oriole O. auratus and Black-headed Oriole O. larvatus from November to February. The three similar-sized oriole species occur together in the main woodland types in different densities (HERREMANS 1997). While oriolus and larvatus show greater plasticity in habitat selection, auratus is more restricted to miombo woodlands where it outnumbers the other two species. In all habitats, the Palearctic species is least common among the three with a slight preference for mopane woodlands. O. oriolus is a nomadic winter visitor feeding at most abundant food resources and does not establish territories. Especially in miombo woodlands it gets into contact with its sibling species O. auratus. I compared habitat structure and use of foraging habitat among the three oriole species. Behavioural observations on reaction to playback, foraging movements, interspecific interactions and comparison of morphological data yielded additional information about the interspecific relationships at places where all three species were present. Breeding O. auratus were aggressive towards and dominant over migrant oriolus. Few conflicts were observed between O. larvatus and O. oriolus. O. oriolus and auratus broadly overlapped with respect to habitat structure and foraging habitat use. O. larvatus and oriolus showed significant horizontal and vertical separation. O. larvatus preferrably fed in lower strata, more inside the trees and more often used stems and trunks for foraging. The two other species foraged higher up and in the outer crown area. Wing use during feeding movements was more obvious in the long-distance migrant O. oriolus and the partial intra-African migrant O. auratus than in almost resident O. larvatus. Morphological data (wing, bill, feet) support the tendency toward more arial behaviour of the migratory species, but this requires more detailed study. During the rainy reason, insect and fruit abundance reached a seasonal peak in deciduous woodlands. Orioles especially preferred (hairy) caterpillars. Both miombo and mopane woodlands consist of few dominant tree species and are well known for infestations with phytophagous insects. Seasonally abundant food resources appear to be large enough to support both the breeding African orioles as well as the more flexible nomadic Palearctic migrant.

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