Weather conditions are systematically associated with long-range nonroutine movements in a large scavenger

Jacopo Cerri , Ilaria Fozzi, Davide De Rosa, Fiammetta Berlinguer, Chiara Costantino 

Movement data are valuable for the conservation of Old World vultures, as these move across large distances and experience a wide range of threats. As vultures rely on soaring flight, the interplay of solar radiation, as well as wind direction and strength, is crucial for both short- and long-range 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 Griffon Vultures (Gyps fulvus, n.individuals = 20, n. GPS locations = 168,202) living in Sardinia (Italy) engaged in short-range, medium- and long-range movements under different weather conditions, in terms of solar radiation, wind direction and wind strength. Under very weak wind conditions, Griffon Vultures restricted their movements in the areas around the colony, as exploring areas at the borders of their home range is more demanding. Conversely, under very strong winds, extra-home range movements were uncommon as Griffon Vultures could be less prone to venture outside well-known areas. Extra-home range movements were more common for northwestern and southeastern winds of intermediate strength, in conditions of good solar radiation. However, the duration of long-range movements decreased with 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 indicates that some types of nonroutine movements in vultures are not entirely intentional and weather conditions can play a crucial role in triggering them. Combining high-resolution movement and weather data could allow researchers to them in advance and adaptively increase improve data acquisition from GPS tags, to study vulture behavior during nonroutine movements and improve conservation actions.