Weather Conditions Are Systematically Associated With Long-Range Nonroutine Movements in a Large Scavenger

Movement data are valuable for the conservation of large soaring birds, as these move across large distances and experience a wide range of threats. As species like Old World vultures rely on soaring flight, weather conditions are crucial for their movements. However, no study explored the extent to which weather conditions can predict long-range nonroutine movements, such as those associated with forays, prospecting, or dispersal. We fitted Generalized Additive Mixed Models to predict the probability that Griffon Vultures (Gyps fulvus, n. individuals = 20, n. GPS locations = 168,202) living in Sardinia (Italy) engaged in short-range, as well as in medium- and long-range movements outside their home range, under different weather conditions, in terms of solar radiation, wind direction, and wind strength. Griffon Vultures restricted their movements around the colony under very weak winds and were less prone to venture outside their home range under very strong winds. Medium and long-range movements outside the home range were more common for northwestern and southeastern winds of intermediate strength, in conditions of good solar radiation. However, the duration of long-range movements increased with decreasing solar radiation. This might indicate that wind sometimes displaces Griffon Vultures and scarce solar radiation then prevents them from returning to the colonies, forcing them to engage in long journeys across unfamiliar landscapes. Our findings indicate that some types of long-range nonroutine movements in vultures are not entirely intentional, but rather triggered by weather conditions. Combining high-resolution movement and weather data could allow researchers to predict these movements in advance and adaptively increase data acquisition from GPS tags to study vulture behavior during nonroutine movements and improve conservation actions.