Acclimatization length and post-release spatial cohesion in translocated Griffon Vultures (Gyps fulvus)

Translocations are often used in the conservation of large raptors, including Old World vultures. Different release methods are usually assessed by comparing the movement patterns and survival of released individuals. However, these approaches fail to capture the gregarious behaviour of many vulture species. We assessed the post-release spatial behaviour of four cohorts of Griffon Vultures Gyps fulvus in Sardinia (Italy), comparing birds released at one site after long (15 months, n = 7) acclimatization periods with those released in another site after short (3 months, n = 16) acclimatization periods. We quantified biweekly occurrence distributions and modelled temporal trends to assess whether long-acclimatized Griffon Vultures were faster and more prone to (i) overlap their space use with that of other individuals from the same cohort and (ii) restrict their movements around colonies. Although our results do not allow separation of the effects of acclimatization period, site and release season, our results suggest that long-acclimatized Griffon vultures had a higher intra-cohort correlation in their occurrence distribution. They were also faster at moving between the two main colonies than short-acclimatized ones. After 4–5 years, they were also more prone to use both colonies and thus less prone to remain confined in a single colony for 2 weeks, or to move far away. Our results suggest that long acclimatization periods may promote group cohesion in released Griffon Vultures, probably as a result of the creation of stronger inter-individual bonds at the aviary, which can then facilitate movement at release sites and explain their faster use of a multiple colony system. Long acclimatization periods (>12 months) should be preferred for translocations of gregarious vultures, as they foster group cohesion and can facilitate post-release survival.