The behavioral trade-off between thermoregulation and foraging in a heatsensitive species

The range-shifts of many species are lagging behind climate change, meaning that those species are likely to experience increases in average ambient temperature. Heat-sensitive species may experience increasingly precarious trade-offs between investment in ther- moregulation versus other key processes as the climate warms. We investigated the potential for trade-offs to exist between behav- ioral thermoregulation and foraging, studying a typical heat-sensitive endotherm: the Alpine ibex (Capra ibex). Ibex use higher altitudes when it is hotter, which could restrict them from more profitable foraging areas at lower altitudes. We investigated this potential trade- off using data on the altitude-use and activity budgets of 43 marked males collected during the vegetation growing season in Gran Paradiso National Park, Italy. We used structural equation modeling to assess the support for models linking ambient temperature, altitude-use, vegetation productivity, and foraging time. Ibex migrated to higher altitudes during spring and summer, maintaining their ambient temperature within a very narrow band. Consequently, when it was warmer ibex utilized areas that were less productive, as indicated by lower normalized difference vegetation indices, and consumed lower quality forage, as indicated by lower levels of fecal crude protein. Ibex did not compensate behaviorally for reduced forage productivity by adjusting their foraging effort. We identify a trade-off between thermoregulation and foraging in ibex, which could affect this species negatively in the future. Such trade-offs could be a general phenomenon for heat-sensitive species. Our study reveals that behavioral thermoregulation can exert a strong influence on animal distributions, even overriding resource productivity in importance.