Abstract:
In the Palearctic-African bird migration system, some studies have addressed the question of coexistence of Palearctic breeding birds with Afrotropical species in the former‟s wintering grounds, however, conclusions are often drawn in a speculative way. These studies have led to some generalizations concerning habitat selection and foraging ecology about the traits that might enable migrants to coexist with residents. Migrants are often assumed to be more diverse in their habitat selection, forage in higher up in the vegetation than residents are, and more flexible in foraging behaviour by using a wider range of foraging techniques, though some studies revealed contradicting results. I studied the foraging ecology
and resource partitioning of Palearctic migrants and resident birds in Northern Ghana, with emphasis on spatial partitioning, foraging techniques and habitat preference. I compared the ecology of three Palearctic breeding species: Ficedula hypoleuca, Hippolais polyglotta and Phylloscopus trochilus, with three resident species: Cisticola rufus, Eremomela pusilla and Sylvietta brachyura. All migrating species were more flexible in foraging behaviour as compared to their Afrotropical counterparts. The present study suggests that migrants partition resources with residents and, therefore, coexist with Afrotropical species. The generalization that migrants forage higher up in the vegetation strata was also confirmed. However, with respect to habitat usage, I could not fully confirm the above-mentioned generalization, since Rufous cisticola showed higher diversity in habitat usage than the Melodious warbler, showing that care has to be taken into account when drawing general conclusions from few studies for a whole migration system on a huge continent.
Differences in habitats used by resident warblers during the presence and absence of migrants were significant. Similarly, Northern crombec and Rufous cisticola were found to forage higher in the vegetation when migrants were present than when they were absent. This difference could be as a result of niche shift induced by the arrival of migrants. However, it is not known which mechanism facilitates this separation because interference competition was not observed. A social survey conducted on the study site suggested that certain activities of local inhabitants could pose a threat to the survival of migrants.
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