Date of Award

1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

J. V. Remsen, Jr

Abstract

South American austral migrants are bird species that breed in temperate South America in the southern summer and migrate north, towards or into northern South America, for the southern winter. Austral migration is similar to other avian migration systems in many ways, but its uniquely South American locale is reflected geographically by the relatively short-distance migrations of most austral migrants, and taxonomically by the numerical dominance of the suboscine family Tyrannidae (the tyrant-flycatchers), of which more than 70 species migrate. Detailed examination of the distributions of austral migrant flycatchers revealed that each is to some extent unique, but that discernible general patterns exist. The latitudinal distribution of austral migrant flycatchers seems to be related to that of resident flycatchers, indicating that the same factors are probably affecting both groups, but in different ways. Breeding austral migrant flycatchers are most diverse around the borders of the Gran Chaco, and wintering flycatchers in and around southwestern Amazonia. Most austral migrant tyrannids breed in scrubby or woodland habitats, and breeding and wintering habitats tend to be similar. The Amazonian microhabitats occupied by wintering austral migrant flycatchers also tend to resemble their breeding habitats, rather than the more complex parts of Amazonian rainforest. Climatic factors, especially temperature, play a greater role in the breeding distribution of austral migrant flycatchers than does habitat, consistent with the results of Herrera (1978) for Europe and Willson (1976) for North America. The evolution of passerine austral migration among Neotropical lineages seems to be tied to movement patterns within the tropics, in partial agreement with Levey and Stiles (1992). Austral migrants tend to be drawn from lineages characterized by occupation of canopy, edge, and open habitats and by dietary opportunism; these attributes were likely important evolutionary precursors to temperate-tropical migration.

Pages

302

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