Predicting Distributions of South American Migrant Birds in Fragmented Environments: a Possible Approach Based on Climate

Abstract

15.1 Introduction Migratory species pose unique challenges to conservation. They have three distributions: their breeding distribution, an often widely disjunct nonbreed-ing distribution to which they migrate after breeding (often termed the win-tering distribution), and the intervening areas through which they move and stop over in passage. Their conservation, therefore, requires knowledge of dis-tribution patterns in spatial and temporal terms. In the context of habitat fragmentation, migratory birds that breed in southern South America offer further challenges. Many migrate after breeding to the vastness of Amazonia, where rapid field surveys or studies of community ecology are not always fea-sible. Furthermore, Tuomisto et al. (1995) showed that Amazonian environ-ments are more heterogeneous or, in a sense, more naturally fragmented than previously suspected. Potentially, this indicates even more difficulties in ade-quately describing the seasonal distributions of migrant birds there. Some method of predicting or modeling distributions of migrants in space and time in areas such as Amazonia would therefore be useful. For example, a modeled migratory pathway could be a layer in a geographic information sys-tem (GIS) along with layers showing extent of habitat fragmentation on local or regional scales. In that way, often-scarce resources might be more effec-tively channeled into fieldwork to obtain still badly needed data on the nat-ural history and ecology of migrant birds. It is my general aim in this chapter, then, to explore a possible method of such prediction. I will focus on migrant birds that breed in southern South America, so a brief review of their migration patterns is appropriate (see also Joseph 1996). The prevailing view of their migration patterns has combined elements of cli-mate and latitude and has been accompanied by widespread use of the term " austral migration " (e.g., see introductory sections of