Juliet Vickery's scientific contributions

The nature of the mechanisms that may structure ani-mal communities is much debated and the role of inter-specific competition in particular is difficult to detect in the field (Huston 1994). In many situations it is only possible to monitor putative mechanisms of niche par-titioning that might enable species to coexist. The role of the interspecific interactions that occur when large numbers of migrant birds join resident communities in their winter quarters has been reviewed by Greenberg (1986) and Leisler (1992), who suggested that compe- Palearctic migrants are thought to coexist with resident species in sub-Saharan Africa by foraging in more open habitats and by being more flexible and opportunistic in their foraging behaviours and utilisation of resources than their Afrotropical counterparts. We assessed how migrant willow warblers Phylloscopus trochilus partitioned resources with two ecologi-cally similar resident warblers, the burnt-necked and green-capped eremomelas Eremomela usticollis and E. scotops, in acacia, miombo and mopane woodlands in Zimbabwe during the northern winter of 1999–2000. We examined whether foraging willow warblers differed from residents in microhabitat selection and food intake rates, and whether they used a wider range of foraging tactics. Unlike either eremomela species, willow warblers occurred in all three habitat types. In acacia they showed a significantly greater diversity of feeding tech-niques, perhaps reflecting a greater diversity of prey taken, compared to the burnt-necked eremomela. In miombo, however, willow warblers did not differ significantly in feeding reper-toire from the green-capped eremomela, but did show a significant difference in feeding mi-crohabitat within the vegetation. In mopane woodland, where eremomelas hardly occurred, willow warblers showed the highest diversity of feeding techniques and may be able to ex-ploit resources there that eremomelas cannot. Although there may be some microhabitat dis-placement and niche partitioning between willow warblers and eremomelas, we do not know which mechanism facilitates this separation, when it exists at all, because direct interspecific interactions were virtually nonexistent. We cannot yet assess the extent to which such inter-actions, together with the willow warbler's apparently greater behavioural flexibility, might fa-vour its coexistence with the local community of ecologically similar arboreal insectivores.