Aim To evaluate the relative effectiveness of the lower and upper sections, respectively, of the Amazon River as a barrier to bird distribution, and to evaluate ecological and taxonomic factors affecting the efficacy of the river barrier.Location Amazon River of South America between its confluence with the Napo River in the west and its delta in the east.
In the temperate latitudes of South America, populations of many species of austral bird migrants move northward from their breeding grounds to warmer latitudes during the austral winter. We identify 35 species of birds that presumably nest in Paraguay but are absent or rare during the winter (northern austral migrants), and 45 species with populations that winter in Paraguay but breed in areas farther south (southern austral migrants). We summarize the status of each species and justify its recognition as a longdistance migrant by providing extreme dates of occurrence or other pertinent observations. New distributional records and extreme migration dates are reported for many species. The austral migrant fauna is dominated by flycatchers (Tyrannidae), which account for 40% of the species. Most species of austral migrants are insectivorous.
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