Models of poisoning effects on vulture populations show that small but frequent episodes have a larger effect than large but rare ones

Abstract

Abstract. Vultures are among the most threatened avian taxa in the world. When vultures aggregate in large numbers to feed, poisoned carcasses can extirpate entire populations at once. In the light of shrinking numbers worldwide, restocking and reintroduction projects, where wild or captive-bred vultures are released back into nature, constitute a crucial management tool, successfully implemented in many countries. However, reestablishment of sustainable vulture populations to their historical ranges remains a serious challenge, especially if the threat of poisoning persists, which is usually the case. In this study, we model the outcome of a restocking project where an initial colony is subject to repeated poisoning events. We use as an example the isolated population of the griffon vulture (Gyps fulvus) in Cyprus. Mathematical considerations and model simulations show that the probability of colony persistence depends on the initial population size and the intensity and frequency of the poisoning incidents. This type of scenario creates an Allee effect that requires a colony to exceed a minimum size in order to survive. Also in this scenario, a sequence of small but frequent poisoning episodes is worse on average than a few large and rare ones of the same cumulative mortality. Future population reinforcement efforts for vultures should focus on the release of adult birds in adequate numbers for the successful establishment of sustainable colonies and should involve a reduction in small but persistent sources of mortality such as the poison baiting of small canids that until now has been neglected by conservation scientists.

Value of combining transect counts and telemetry data to determine short‐term population trends in a globally threatened species

“…This is particularly concerning given recent findings by Rigas et al. (2021) that even small, but frequent, poisoning events can have devastating consequences.…”

“…While our number of confirmed large poisonings is small, many of the presumed mortalities (n = 8) or those with unconfirmed cause (n = 12) were suggestive of smaller poisoning events, based on tags having been removed or the location of death being near park boundaries. This is particularly concerning given recent findings by Rigas et al (2021) that even small, but frequent, poisoning events can have devastating consequences.…”

Results of the re-introduction of the Griffon Vulture (Gyps fulvus) in Vrachanski Balkan Nature Park, Bulgaria – completion of the establishing phase 2010–2020

“…The success of intensive GPS tracking and fast reaction in the field is especially relevant to large, infrequent poisoning episodes, such as the ones from Kresna Gorge in 2017 ( Peshev et al 2019 ) and Vrachanski Balkan in 2019 ( Peshev et al 2022 ). However, Tsiakiris et al 2021 state that frequent minor poisoning episodes could harm marginal vulture colonies and populations much more. Thus, a holistic and wide-spectrum fight against poison use should be ongoing.…”

Griffon Vultures restrict movements around roosts and supplementary feeding stations, even when carrion is available on the field: a call for wind energy zonation to avoid ecological traps on Mediterranean islands

“…Absent any zonation, mitigation and mapping of wind energy development, by considering that up to approx. 6,700 turbines could be built by 2030 (https://www.anev.org/wp-content/uploads/2022/07/Anev_brochure_2022.pdf) and that the last available data refer to 2019, the griffon population in Sardinia could experience frequent mortality events, which could in turn lead to severe density-dependent dynamics undermining its viability [55] . (2021a) [56] https://doi.org/…”