Abundance and diversity of small-bird assemblages in the Monte desert, Argentina

Abstract

Assemblages of small bird species (o90 gbody mass) from the Monte desert in Argentinawere studied to analyze spatial and temporal variation in abundance and species richness.Mean species richness was higher during breeding season than in non-breeding season. Thesame pattern was observed in aerial insectivores, while granivores and substrate insectivoresdid not differ between breedingand non-breedingseasons. Overall bird abundance was similaracross seasons. Species richness was positively correlated with bird abundance and negativelycorrelated with dominance; bird abundance and dominance were not correlated. Thesepatterns could be explained by distinct responses of functional groups of birds; dominantspecies were granivores in the non-breeding season and aerial insectivores during the breedingseason, and bird abundance in functional groups changed according to food supply. Mostspecies are residents or regular migrants, while there are few nomadic and transient species.Predictable annual fluctuations in rainfall and resource availability should favor a migratorystrategy more than nomadic movements. Similarly, breeding is strongly seasonal and mostspecies start breedingwhen the first summer rains have generally not yet fallen. Finally,concordances in assemblage structure at local and regional scale suggest that similarmechanisms are actingon the local bird assemblages across the Monte.