Temporal beta diversity of bird species using the point count method indicates predominance of turnover over nestedness in an Atlantic Forest site

Morning is the ideal period for sampling bird communities in tropical forests, but there is a vocal decline in birds over time. We investigate the variation in species richness and composition between six morning periods in a tropical rainforest in Brazil and the implication of this decline on the adaptability of the point count method. The study aimed to optimize the point count method, evaluating how many points are needed to obtain satisfactory species richness and composition data. The results showed that the first four periods of 15 min after sunrise are the most effective as they cover more than 96% of total species richness, with a peak in species richness in the second and third periods. However, taxonomic composition showed an average beta diversity of 28.1% among the morning periods, with turnover dominating over nestedness. The later morning periods added only a small number of new species, with some species having associations with specific time periods. Thus, the most important sampling range for ornithologists interested in species richness is the first four periods, corresponding to a total duration of 1 h and 45 min after sunrise. However, a researcher interested to investigate species composition, where habitat species composition is desired or the recording of specific species, a longer stay in the field is indicated, because the longer the time spent in the field, the greater the chances of recording locally rare species.

Automated summary

This study investigated the variation in species richness and composition of bird communities in a tropical rainforest in Brazil over six morning periods. The results showed that the first four 15-minute periods after sunrise were the most effective for sampling, covering over 96% of total species richness. However, the taxonomic composition varied among the morning periods, with turnover dominating over nestedness. Researchers interested in species richness should focus on the first four periods, while those interested in species composition or specific species should spend more time in the field.