Studies of Brazilian birds along altitudinal gradients: a critical review

Brazil is home to many mountain ranges which harbor diverse avifauna. However, studies on the altitudinal distribution of Brazilian birds are still few and many have never been published, hampering both the dissemination of basic information and conservation actions. Here we present a critical review of ornithological studies undertaken in Brazilian mountain ranges, and propose a classification of geographic scope, altitudinal gradient, and methodology. Since 1922, 184 ornithological studies included altitude in some way in Brazil, encompassing a variety of research topics and species. About a quarter of these studies were never published in peer-reviewed journals, and 39% do not provide basic data on elevation nor link the bird species with sampling plots, thus limiting their applicability. The majority of studies are concentrated (83%) in southern and southeastern Brazil, especially in the Serra do Mar range, and so most data are associated with the Atlantic Forest. Gaps remain in other regions, such as Amazonia (Pantepui region). Most studies either did not sample the entire elevation gradient, were not standardized, lacked explicit hypothesis, or did not account for a seasonal sampling embracing the four seasons of the year, so interpretation of the observed patterns remains difficult. With this compilation, we organize the available information and point to future altitudinal research on birds, in addition to highlighting the importance of preserving habitats along altitudinal gradients in the mountainous regions in Brazil.