Water Use Behavior of Individual Birds: Ring Ouzels in an Arid High-Mountain Ecosystem.

Water availability strongly constrains animal behavior in arid ecosystems. Species relying on low-water diets must balance hydration needs with foraging, thermoregulation, competition, and predation risk. While most studies focus on species-level responses, less is known about how individuals within populations differ in water-related behavior. Here, we examine individual and population-level variation in water-use patterns in a small wintering population of ring ouzels (Turdus torquatus) within an arid high-mountain ecosystem on Tenerife (Canary Islands), using camera trapping and individual recognition during the 2022-2023 wintering season. We analyzed multiple components of water-use behavior in relation to ambient temperature, social context, and dominance status. Drinking probability during visits (70% on average) and visit duration increased with temperature, consistent with rising thermoregulatory demands, although individual responses differed among water sources. Bathing behavior showed a consistent quadratic relationship with temperature across individuals, peaking at intermediate values (∼15°C). Social context also shaped behavior: Drinking probability increased with the number of conspecifics, whereas visits were shorter when more birds were present. Dominant individuals made more visits, drank more frequently, and consumed larger daily water volumes-up to 30 mL (∼30% of body mass)-than subordinates, revealing unequal access to water within the population. Together, our results demonstrate that environmental heterogeneity and social hierarchy jointly structure access to a critical resource, generating pronounced intra-specific behavioral variation. As aridity intensifies under climate change, individual behavioral flexibility and social dynamics may play a key role in determining population persistence and the maintenance of bird-mediated ecosystem functions.