Seasonality in niche occupation revealed through bird community functional structure in the southern Atlantic rainforest

Abstract

Seasonal variation in tropical and subtropical systems can have different effects on bird species depending on the resources they use and how they use them. However, despite recent research advances, knowledge of the drivers of the presence and abundance of species in different seasons is still limited for most tropical bird species. In these poorly understood systems, examining seasonal changes in species composition from the perspective of traits related to resource use can provide insight into what resources may be driving bird movements between areas throughout the year and what types of species are more subject to seasonality. Here, we explore bird community seasonality in three forest types (dense, semi-deciduous and mixed rainforests) subjected to different climatic conditions in one of the world's biodiversity hotspots, the Atlantic Rainforest. We investigated differences between summer and winter in species richness and in the composition of resource-related species traits (diet, foraging strata and substrates) obtained from the literature. The seasonal differences (summer and winter) between forest types were explored in terms of species and trait composition. We found that the main changes that occurred in bird composition between seasons in the southern Atlantic Rainforest were related to species traits such as diet and foraging strata. In general, the proportion of invertivores was higher in winter than in summer, and in the mixed forest, the forest type exposed to the coldest winters, the proportion of frugivores was lower in winter. Furthermore, species with a more varied diet were better represented in the summer. In general, more generalist species were better represented in the forest type subjected to higher seasonal variations in rainfall. Our results revealed seasonal changes in bird community structure that are related to niche occupation and that were more strongly apparent in the forest type subjected to colder winters.