Spatial and trophic ecology of the estuarine Little Tern Sternula albifrons

Little Terns Sternula albifrons are estuarine birds extensively using increasingly urbanized coastal areas. Given the increased exposure of these ecosystems to anthropogenic activities, it is crucial to study the ecology of this species and interactions with human stressors to establish management measures. We collected regurgitates (n = 182) and blood samples (n = 48) to study Little Terns' diet, health condition and isotopic niche, and individually tracked breeding adults (n = 9, during 2021 and 2022) at 2 sandy beaches 21 km apart and located within Ria Formosa Natural Park, Algarve, Portugal. Although both areas are adjacent to foraging coastal marine areas and an estuarine lagoon system with saltpans, they differ in human disturbance. We also compared breeding success and adult health measures between these 2 colonies. The main prey for both populations were Sand Smelts Atherina spp. and Gobies Pomatoschistus spp., and no differences in δ ¹³C and δ ¹⁵N stable isotopic values between colonies were found. Tracking data revealed that individuals foraged in the surroundings of their breeding colonies. Entrance Channels and Ocean were the most frequently used habitats for foraging by individuals from the less disturbed colony. Adults from the more disturbed colony foraged mostly in Entrance Channels. Overall, all individuals tended to forage during daytime. There were no differences in health measures of individuals between colonies, though breeding success at the most disturbed colony was comparably lower. It is important to protect both breeding areas and adjacent foraging habitats for Little Terns, particularly given the expected increasing pressure from human activities on coastal areas worldwide.