Habitat selection and coexistence of migrants and Afrotropical residents

Abstract

In this paper I discuss factors that influence the habitat choice of small migrant birds on their Afrotropical wintering grounds and the ecological isolation of migrants and residents. The main characteristic of migrants is the use of resources which are sporadic in space and time. The majority of migrants occur in seasonal savannas and open woodland, mostly using temporarily and locally abundant food sources generally unused by residents. Migrants are more eurytopic and exploit more open parts of the habitats than ecologically similar tropical species. In some guilds, the foraging speed and rate of migrants is higher and they use their wings more often in comparison to residents, There is weak evidence that niche shifts of residents are induced by the arrival of migrants. Overt interspecific interactions seem to be infrequent, except in a guild of ground-feeding birds which rely on a rather predictable but poor food supply. In this guild, residents, but not intra-African migrants, dominated Palaearctic migrants in aggressive encounters irrespective of body-size. In contrast to this, dominance was sizedependent among wintering Palaearctic migrants.Several external as well as internal factors determine habitat selection by birds in their winter quarters. Competitors and food availability have always been regarded as important factors in habitat selection. The objectives of this paper are to discuss which habitats migrants choose in their Afrotropical winter quarters and how they coexist with local resident species. It focuses on possible competition between small migrant land birds and ecologically similar Afrotropical species, and their differences in resource use. In the first section, information is summarized on the biogeographical background and the ecological setting of the wintering habitats, based mainly on works of Morel & Morel ( 1978). jones ( 1985). Morel I 1989) and on recent reviews of the Palaearctic-African system by Lovei ( 1989) and Lack ( 1990). In the second part, I will discuss some results from comparative studies, reviewing the literature and referring to my studies of wintering and native chat-like thrushes in Kenya (Leisler et d. 1983. Leisler 19901. ECOLOGY OF THE WINTERING AREAWhen dealing with the problem of coexistence of migrants and residents, it is important to outline which regions and which habitats migrants choose as their winter quarters. More species and birds winter north of the equator than south: about two-thirds of individuals and about 40% of species that cross the desert into Africa remain in the northern tropics (e.g. Elgood et al. 1966, Curry-Lindahl 1981, Brown et al. 1982 The majority of migrants in Africa occur in seasonal savannas and light woodland of various kinds (Lovei 1989, Lack 19901. Migrants make up only about 4% of the birds in mature tropical rainforests (Brosset 1990, Lack 1990. This is in marked contrast to the importance of rainforests in the Neotropics (e.g. Terborgh 1989) and t h e Sunda region (Wells 19901. Although the contribution of migrant...

When David Beats Goliath: The Advantage of Large Size in Interspecific Aggressive Contests Declines over Evolutionary Time

“…In the case of woodcreepers, the specialized adaptations for tree climbing [50] enhanced their performance in aggressive contests with some woodcreeper species on tree trunks [38]–[40], but compromised their performance in aggressive interactions with antbirds, which typically occur on small saplings and branches [44], [50]–[52]. In the case of migration, a fundamental trade-off appears to constrain the ability of species to excel at both migration and performance in aggressive interactions simultaneously (Text S3), resulting in smaller resident species dominating larger migrant species across many different environments [14], [53]–[55] …”

Bird migration in the southern hemisphere: a review comparing continents

“…Several authors have noted differences in the primary habitat associations of migrants among the three major flyways (e.g. Leisler 1992;Mönkkönen et al 1992;Hockey 2000Hockey , 2005Boyle and Conway 2007), thus raising the question of what influences habitats may have in the different southern continents. In the western Palaearctic most migrants are denizens of early successional stages and more open habitats.…”

Habitat Use and Body Mass Regulation among Warblers in the Sahel Region during the Non-Breeding Season

“…Compelling evidence for the role of inter-specific competitive exclusion in the shaping of migrant and resident communities in the wintering grounds is lacking [2], [10], [12]. However, evidence for such competitive exclusion in an intra-specific context was provided by Perez-Tris and Telleria (2002) [23], who showed that resident blackcaps Sylvia atricapilla breeding in southern Spain maintained their breeding territories in primary forest habitats into the non-breeding season, while migrant blackcaps arriving at the start of the wintering season ‘leap-frogged’ into the secondary (lower quality) scrub habitats not occupied by residents.…”

“…adaptable) and have less restrictive habitat requirements during the non-breeding season, allowing them to use a wider range of winter habitat types than ecologically similar but more specialised resident species [2], [21], [24]. Such adaptability and breadth of foraging strategies has been shown in wintering golden orioles Oriolus oriolus , which were, by virtue of their wider range of foraging tactics, able to survive in lower quality microhabitats than were preferred by resident species [25].…”

“…Most of these species are restricted to either wetland or scrub habitats, but three are relative habitat generalists: Eurasian reed warbler regularly occupies dry scrub, while subalpine warbler and chiffchaff often forage in the ecotone between scrub and wetland habitats. Such use of multiple winter habitat types by warbler species is well known [2], [55], [56]. Furthermore, there appears to be significant intra-specific variation in the body reserves (in the form of fat and pectoral muscle) of birds wintering in West Africa [57], [58], although the reasons for such variation are unknown.…”