Sampling Bias of Birds in the Pantanal Wetland: A Study Case with Records from Biological Collections

Biological collections provide valuable data for studying biodiversity patterns and processes. However, they often suffer from taxonomic, temporal, and spatial biases frequently driven by accessibility, sampling methods, or collector preferences. The Pantanal is one of the largest wetlands worldwide and has the greatest richness of bird species for this type of ecosystem. Birds provide different ecosystem services and despite being extensively studied, biases still exist in this group. Our research aimed to investigate taxonomic, spatial, and temporal (historical and seasonal) sampling biases for birds in the Pantanal. We compiled 4,066 records of 363 species from 20 collections readily available in biodiversity repositories, ranging from the years 1823 to 2019. Our results revealed that almost 95% of the Pantanal remains unsampled, especially the central region, with a strong effect of accessibility on sampling. Records were concentrated during the period with less flooding, indicating seasonal bias. Furthermore, 41% of bird species presently known to occur in the Pantanal lacked a record in the database. Passeriformes were three times more recorded than "non-Passeriformes". The intense use of mist nets can be driving this difference since it favors the sampling of small species, such as most Passeriformes. Our results reinforce the effect of accessibility and sampling methods on data collection, demonstrating that flood seasonality can be an additional factor for sampling biases in wetlands. Therefore, strategies to reduce these biases are necessary and can contribute to increasing the ornithological knowledge and comprehension of the ecosystem functioning of the Pantanal.