Egyptian Vultures
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Increase survival and number of breeding pairs of released Egyptian vultures
Data collection in progress
Iron Curtain to Green Belt
Bulgaria
Problem: The project area is a national stronghold for the breeding population of the Egyptian vulture, an IUCN red listed species. However, current threats to the species include persecution, particularly poisoning, and a loss of suitable habitat for breeding and supporting prey species, mainly through the conversion of grasslands and scrub to arable farmland. The population is currently small and restricted to the westernmost part of the landscape.
Action: Over the ELSP funding period, at least 30 Egyptian vultures will be released into the landscape to reinforce the small existing population. Mitigation and education activities will also be undertaken to improve human-wildlife coexistence and reduce persecution, and grassland and treeline restoration will provide more suitable habitats for the species.
Indicator: The survival of Egyptian vultures released into the landscape, and their subsequent inclusion in the breeding population, will be used to assess the success of the reinforcement programme. Further, the overall number of breeding pairs and occupied territories are key indicators for the species status and its population trend more generally within this landscape.
Photo: Svetoslav Spasov
Photo: Svetoslav Spasov
Methods
The BSPB has a long-term Egyptian vulture monitoring programme with an established methodology. To monitor survival, all Egyptian vultures released into the wild under the reinforcement programme are marked with GPS/GSM transmitters. This yields data that can be categorised into four observable events:
- functional tags on a moving animal
- functional tags that were not moving, indicating potential death
- bird carcass recovered or other confirmed death
- no transmissions received
This data is used to create multi-event capture–recapture models, also incorporating one of three states for each bird: alive with functioning transmitter, alive without functioning transmitter or dead (for full details see Oppel et al. 2021). The models are used to estimate the probability of survival from one month to the next. Annual survival can be estimated by multiplying the respective monthly survival estimates over each year of life. Survival is calculated over two time periods: (1) until the end of the first southward migration (the period of highest mortality for young vultures, with 41% birds dying within 6 months of fledgling), and (2) until reaching adulthood.
To assess number of breeding pairs and breeding success, all territories occupied the previous year are visited at least three times during the breeding season (see Arkumarev et al. 2018 for full details). A territory is defined as occupied when display, courtship behaviour or nest building are observed. The first visit takes place in late March/early April to establish which territories are occupied by pairs. The second visit takes place in May to determine which pairs are breeding. The third visit takes place in June, to count any chicks, and the fourth visit in August counts fledglings, if any.
Meanwhile, potential and historic breeding sites in the area are checked for new pairs. All observations are made from stationary viewpoints located at distance greater than the mean maximal alert distance of the species (605 m) to avoid disturbance. At least two hours of observation will be done in each territory during each visit. The data from the GPS transmitters of the released individuals will also be used to determine their breeding status.
Results
The baseline number of breeding pairs of Egyptian vultures in the project landscape in 2023 is 21 pairs (see graph below).
In 2023, two vultures that hatched in 2022, Luis and Paulina, were tagged and released on 5 May, using the delay-release approach. Unfortunately, in June Paulina died in the vicinity of the release site, probably due to predation. Luis survived and finished its first migration, successfully reaching the wintering grounds in Yemen. Hence, the survival rate of released Egyptian vultures at the end of the first south migration in 2023 is 0.5, below the average of 68.4% (n=21) across all years since 2016.
The survival rate of released individuals since 2016 is shown in the figure below. So far, the results demonstrate that the survival rate of individuals released with the delayed release method have the highest survival rate at the end of the first south migration, exceeding the survival of the wild juveniles.
Survival rate of released individuals since 2016, by release method.
We will continue to update this page throughout the ELSP funding period, as more data becomes available.
References
Arkumarev, V., Dobrev, V., Stoychev, S., Dobrev, D., Demerdzhiev, D., Nikolov, S.C. 2018a. Breeding performance and population trend of the Egyptian Vulture Neophron percnopterus in Bulgaria: conservation implications. Ornis Fennica, 95: 115-127.
Oppel, S., Saravia, V., Bounas, A., Arkumarev, V., Kret, E., Dobrev, V., Dobrev, D., Kordopatis, P., Skartsi, T., Velevski, M., Petrovski, N., Bino, T., Topi, M., Klisurov, I., Stoychev, S. and Nikolov, S. 2021. Population reinforcement and demographic changes needed to stabilise the population of a migratory vulture. Journal of Applied Ecology, doi: 10.1111/1365-2664.13958
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