Seasonality determines bird abundance, richness, and diversity among contrasting forest environments in the Northern Pantanal

Seasonally flooded ecosystems are comprised by heterogeneous vegetation mosaics (i.e., environments), wherein habitat availability and food resources are spatially and temporally variable. Overall, these factors determine the abundance, richness, and diversity of birds. To evaluate season- and environment-dependent bird abundance, richness, and diversity, we sampled understory birds along two seasons (dry and wet) in three forest environments, i.e., one semideciduous non-flooding forest (Cordilheira) and two evergreen flooding ones (Cambarazal and Landizal), in the northern region of the Pantanal. Birds were captured using mist nets that were located in four sites for each environment between 06:00 h and 11:00 h, during 3 months in the dry season and 3 months in the wet season. We captured 505 individuals from 21 families and 70 species of understory birds. Seasonality significantly affected bird composition, with higher abundance, richness, and diversity in the dry season. Indeed, most of the individuals were captured in the dry season (n = 365), comprising 62 species and 20 families. During the wet season, we captured 140 individuals from 38 species and 15 families. Although the Landizal, an evergreen flooding forest environment, comprised a number of individuals about 20 and 40% higher than the Cambarazal and the Cordilheira, respectively, we did not detect any significant difference in understory bird composition among environments. This study reinforces the assumption that seasonality determines understory bird abundance, richness, and diversity, which increase during the dry season, in the Pantanal. We suggest that this pattern is related to higher habitat and food resources availability during the dry season.