Abstract
The current study analyses and presents the results of the ten-year establishment phase of the Griffon Vulture (Gypsfulvus) local re-introduction in Vrachanski Balkan Nature Park, north-western Bulgaria. Between 2010 and 2020, 61 rehabilitated and captive-bred Griffon Vultures from Spain, France and several European zoos were released from an acclimatisation aviary. The first successful breeding in the wild was reported in 2015. Thus, the species has been restored as a nesting species in the area after more than 60 years of absence. In 2020, the local population accounted for some 55-70 individuals, consisting of about 20-23 breeding pairs in three-five separate colonies and two frequently-used roosting sites. Forty-two chicks fledged from 2010 to 2020, at an average breeding success of 0.46 chicks/territorial pair and productivity of 0.62 fledglings/breeding pair. The mortality rate is calculated at 0.34; an additional 0.07 of the released individuals have never been seen or found. The local nucleus of the Griffon Vulture now covers a territory of 1,478.58 km², calculated as a 95% home range, while the 50% core area is 9.07 ± 5.73 km(2) (range 2.12-22.89 km(2)). With these results, we consider the establishment phase of the re-introduction of the species in Vrachanski Balkan Nature Park as completed.