Extreme temperatures impede the release success of captive-bred avian scavengers

Abstract

Conservation translocations (reinforcements and reintroductions) are central for managing various endangered species, yet, their implementation is logistically and financially challenging. Because many translocations fail due to the mortality of released individuals, identifying and preventing these factors is crucial. Here we examine risk factors affecting the post-release survival of the Griffon vulture (Gyps fulvus). The Israeli population is facing extinction, and the recovery efforts by the local Nature and Parks Authority include supplemental releases of individuals from captive-breeding or rehabilitated birds (mostly imported from Spain). We use GPS tracking and thermometers to compare movement, behavior, and weather conditions experienced by released and wild-born individuals active in the same area and time. Our results show that the Judean Desert release site had a significantly lower survival rate than other release sites included in the program. After excluding several possible factors (e.g. known pathogens) with pathological examinations, we found that released individuals at this area were exposed to higher temperatures preceding their death (compared to wild-born griffons nearby), suggesting heat stress as the cause of death. Arguably, they failed to avoid the harsh environmental conditions, resulting in overheating due to their inexperience and undeveloped flight ability, as reflected by their lower probabilities of flying and shorter travel distances per day compared to wild-born vultures. These findings have led to adjustments of the local release protocol, (namely winter releases) resulting in a significant improvement in the early survival of translocated Griffons in the Judean Desert. Accounting for the harmful effects of extreme weather conditions is particularly important in a world facing climate change. More broadly, this sequence of scientific investigation with data integration from ecological, clinical, and biotelemetry sources, leading to improvement in translocation success demonstrates how conservation practices can be optimized by supporting studies to ensure the survival of endangered species in the wild.