Differential survival throughout the full annual cycle of a migratory bird presents a life-history trade-off.

Long-distance migrations are among the most physically demanding feats animals perform. Understanding the potential costs and benefits of such behaviour is a fundamental question in ecology and evolution. A hypothetical cost of migration should be outweighed by higher productivity and/or higher annual survival, but few studies on migratory species have been able to directly quantify patterns of survival throughout the full annual cycle and across the majority of a species' range. Here, we use telemetry data from 220 migratory Egyptian vultures Neophron percnopterus, tracked for 3,186 bird months and across approximately 70% of the species' global distribution, to test for differences in survival throughout the annual cycle. We estimated monthly survival probability relative to migration and latitude using a multi-event capture-recapture model in a Bayesian framework that accounted for age, origin, subpopulation and the uncertainty of classifying fates from tracking data. We found lower survival during migration compared to stationary periods (ß = -0.816; 95% credible interval: -1.290 to -0.318) and higher survival on non-breeding grounds at southern latitudes (<25°N; ß = 0.664; 0.076-1.319) compared to on breeding grounds. Survival was also higher for individuals originating from Western Europe (ß = 0.664; 0.110-1.330) as compared to further east in Europe and Asia, and improved with age (ß = 0.030; 0.020-0.042). Anthropogenic mortalities accounted for half of the mortalities with a known cause and occurred mainly in northern latitudes. Many juveniles drowned in the Mediterranean Sea on their first autumn migration while there were few confirmed mortalities in the Sahara Desert, indicating that migration barriers are likely species-specific. Our study advances the understanding of important fitness trade-offs associated with long-distance migration. We conclude that there is lower survival associated with migration, but that this may be offset by higher non-breeding survival at lower latitudes. We found more human-caused mortality farther north, and suggest that increasing anthropogenic mortality could disrupt the delicate migration trade-off balance. Research to investigate further potential benefits of migration (e.g. differential productivity across latitudes) could clarify how migration evolved and how migrants may persist in a rapidly changing world.

First results from the releases of Cinereous Vultures (Aegypiusmonachus) aiming at re-introducing the species in Bulgaria - the start of the establishment phase 2018-2022.

The current work presents the preliminary results of the Cinereous Vulture (Aegypiusmonachus) releases in the Balkan Mountains in 2018-2022, aiming at the species re-introduction in Bulgaria, where it was listed as locally extinct since 1985. The first imports and releases of Cinereous Vultures in Bulgaria started in 2018. Until mid-2022, 72 individuals were released in the Eastern Balkan Mountains (Kotlenska Planina SPA and Sinite Kamani Nature Park) and Vrachanski Balkan Nature Park. Of them, 63 immatures imported from Spain were released from aviaries and nine juveniles captive-bred in European zoos were released by hacking (fledging from an artificial nest). We compared the success in survival and establishment between the different release sites and methods used to adjust the ongoing technics and tactics and to support knowledge improvement for future similar projects. From the nine Cinereous Vultures released by hacking, the results were as follows: 1.00 fledging success, but only 0.22 survival in the first six months - combined period of acclimation, first migration and the first winter. All survivors from that period reached maturity into the wild, but all emigrated from the release site and settled elsewhere. Of the 63 individuals released by aviaries, 32 individuals were released in the Eastern Balkan Mountains (18 individuals are still alive - 0.56 survival; 14 individuals settled in the area, which accounts for 0.44 of all released birds and 0.78 of the survivors). Thirty-one individuals were released in Vrachanski Balkan Nature Park (23 individuals are still alive - 0.74 survival; 22 individuals settled in the area - 0.71 of all released birds and 0.96 of the survivors). Based only on aviary method comparison, the settling of the individuals in the release area was alike in the two sites. However, the Vrachanski Balkan Nature Park performed better in survival - both in acclimation and establishment periods. While comparing the release methods - hacking and release from the aviary - the following results were observed: the survival rate during acclimation was 0.86. Due to more considerable losses during the first migration and dispersal in the individuals released by hacking, the survival rate of 0.22 was significantly lower compared to 0.73 for the birds released from the aviary. Additionally, in both methods, a similar pattern in the first winter and spring migration dispersal was observed. Although the survival was equal in the released-by-hacking or aviary birds after the first year onwards, it is essential to note that the emigration of the hacked birds from the release site was 1.00. In comparison, the birds released from aviaries largely remained and settled in the release area (> 0.77 of the survivors). The cost of release and related acclimation, settling, dispersal and the first winter was the greatest: 0.12-0.17 per period, or cumulatively, it was about 0.27. Survival increased and stabilised to > 0.90 after the first year in the wild and reached nearly 1.00 after two years in the wild onwards. Two distinct nuclei of the Cinereous Vulture were established along the Balkan Mountains - the Eastern Balkan Mountains with 18-23 individuals and four formed pairs using a territory of about 642.74 km2 - 95% home range and 85.72 km2 - 50% core area with center being the town of Kotel; and Vrachanski Balkan Nature Park with present 23-29 individuals, of which 2-3 pairs formed so far, using a territory of about 1,143.66 km2 - 95% home range and 22.89 km2 - 50% core area with center being the village of Zgorigrad. The species readily accepted breeding in artificial nest platforms built by professional arborists on different tree species - oak, beech, sycamore and pine. The only naturally built nests were on the ground (n = 2) (unsuccessful) and in Scots Pine (n = 1) (successful). In 2021 and 2022, in each of the two sites, the first successful reproductions were recorded, which marked the return of the Cinereous Vulture as breeding species - 28 years after the last occasional record of a single breeding pair in the country and 36 years after it was officially listed as locally extinct in Bulgaria.

Evidence of genetic structure in the wide-ranging bearded vulture (Gypaetus barbatus (Linnaeus, 1758)).

BACKGROUND: The bearded vulture is sparsely distributed across a wide geographic range that extends over three continents (Africa, Europe and Asia). Restriction to high-altitude mountainous habitats, low breeding rates, lack of food and a heightened level of persecution have left many local populations severely diminished or extinct. Understanding the genetic connectivity and population structure of this threatened vulture species is critical for accurately assessing their conservation status, and for appropriately managing local populations through captive breeding programmes or translocations. Previous genetic assessments of the species were mainly focused on the European and Asian populations and included limited representation of the geographically isolated southern African population. A single mitochondrial study, which focused on the African populations of the bearded vulture, detected limited genetic differentiation between populations in Ethiopia and southern Africa, with reduced haplotype diversity in the southern Africa population. In this study, we extend the previous genetic assessments of the species by examining the phylogeography and genetic connectivity of global G. barbatus populations using a panel of 14 microsatellite loci. RESULTS: Analyses revealed spatially correlated genetic differentiation between regional populations and low levels of gene flow between these population fragments. In contrast to the mitochondrial data, the microsatellite data support the management of genetically different populations as separate entities. CONCLUSIONS: Low genetic diversity and geographic isolation are known to adversely affect the evolutionary potential of a species in the long-term. The high inbreeding found in the southern African G. barbatus and, to a lesser extent, the northern African populations highlights the need for conservation programmes to effectively manage populations of this species and maintain extant genetic diversity.