Palearctic passerines in Afrotropical environments: a review

Abstract

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.

Long-term population declines in Danish trans-Saharan migrant birds

“…However, we have little information to conclude that this represents cause and effect (Cresswell et al 2007). Despite the work of several authors (Moreau 1966, Jones 1985, Jones et al 1996, Wilson & Cresswell 2006, until very recently there was lamentably little information on winter distributions and habitat requirements of Palearctic migrants in Africa (Walther & Rahbek 2002, Salewski & Jones 2006, and little understanding of the impact The results of overall ANOVA tests comparing between decades are shown as F-ratio and P values, together with the results of Holm-Sidak multiple comparison tests between decades for each species (indicated as attaining statistically significant differences by 'Yes' or otherwise in the comparisons shown in the right-hand columns). of habitat loss and degradation on wintering Palearctic migrant populations (Baillie et al 2006).…”

The relative importance of conditions in wintering and passage areas on spring arrival dates: the case of long-distance Iberian migrants

“…This problem is accentuated for most of the smaller bodied birds because basic information on their wintering distribution is still scarce or non-existent (Walther and Rahbek 2002;Walther et al 2004;Wisz et al 2007). This gap in our knowledge of species biology is of interest because some species follow different ecological strategies during their breeding season and wintering season, respectively (Jones 1995;Marra and Holberton 1998;Baumann 2000;Salewski et al 2002a;Salewski and Jones 2006).…”

Why are bird migration dates shifting? A review of weather and climate effects on avian migratory phenology

“…Birds coming from the equator must face a minimum rainfall gradient around the tropics (Jones 1995, Salewski & Jones 2006. As a result, rainfall becomes crucial in tropical environments, especially those that are more arid such as the African Sahel, where the alternation of dry and wet seasons is the most important determinant of intrannual variations in ecological conditions (Herrmann et al 2005).…”