Palearctic passerines in Afrotropical environments: a review

Previous ecological studies of Palearctic passerine migrants in Africa have claimed to reveal some general features with respect to habitat use, foraging ecology and interspecific relationships with Afrotropical residents. In this review we discuss apparent contradictions between earlier generalisations and more recent results from more detailed field studies and explore in which areas our ecological knowledge and theoretical understanding remain poor and have given rise to misconceptions. For example, it has been claimed that migrants use structurally more diverse and open habitats and that they forage higher and in more peripheral parts of the vegetation than their ecologically similar Afrotropical counterparts, yet in the past these characteristics were often not clearly defined and not always correlated in practice. It has also been stated that migrants are more flexible in habitat use, occupying a wider range of habitat types and employing a higher diversity of foraging techniques, both of which were assumed to be adaptations to permit coexistence with Afrotropical residents by using untapped resources that are only seasonally available. Yet results from studies of the role of competition in shaping migrant-resident communities remain largely unconvincing. While flexibility may facilitate migrant-resident coexistence, it may also favour the evolution of migration because specialists are less able to use their advantages in different environments. We note that definitions of flexibility and specialisation may themselves depend on the ecological or evolutionary approach adopted by researchers. We conclude that few generalisations can safely be made about the ecology of Palearctic migrants in Africa and that adaptive explanations for the behaviours observed are largely lacking, as are studies of the fitness consequences of different migrant strategies such as have been conducted in the Nearctic-Neotropical migration system.