A version of this blog was originally published online on the Birdguides website (02/01/2022).
On 3rd December 2021, Fundación Migres ringed and GPS-tagged a White-backed Vulture, a vagrant to Europe and the first one to be ringed and tagged in Europe.
The occurrence of this species here – alongside the increased incidence of Rüppell’s Vulture in The Straits – is extremely interesting. Both species are Critically Endangered in their usual sub-Saharan range. It is hypothesised that the increase in Eurasian Griffon Vulture numbers in Europe may be at least partly responsible as this leads to an increase in the number of young Griffons dispersing from and returning to Europe. The largely sedentary African Vulture species mix with young Griffons in The Sahel and get caught up in the return flow of these birds.
Rüppell’s and White-backed Vulture are on the IUCN’s Red List of Threatened Species considered to be Critically Endangered, which is the last category before global extinction.
Satellite tagging these vagrant birds will give us new insights into these Critically Endangered species and aid our conservation knowledge for African Vultures.
The project team decided to name the White-backed Vulture “Viking” in thanks and reference to project partners and funders Viking Optical.
Originally, following presentations and findings at the IUCN Rüppell’s Vulture symposium and given the increasing occurrence of Rüppell’s Vultures in both Southern Europe and North Africa (in particular either North or South sides of The Straits of Gibraltar), the project team had aimed to ring and GPS tag this species at a feeding station.
Since the early nineties, Rüppell’s Vultures have been encountered in the Iberian Peninsula particularly in The Straits of Gibraltar.
The occurrence of normally largely sedentary African Vultures in The Straits is likely to be linked to an increase in Eurasian Griffon Vulture numbers (thanks in no small part to Spanish conservation efforts). The resulting increase of Eurasian Griffon Vultures migrating to the Sahel and mixing with the declining African Vulture populations has meant that when the two species encounter each other, some Rüppell’s or White-backed Vultures get caught up in the “conveyor belt” of the pre-nuptial Griffon Vulture migration and make their way into North Africa and sometimes on to Europe.
We know from existing telemetry data that some of the birds that have made it as far as Morocco have even returned to the Sahel.
One possible future issue for the critically endangered African Vulture population could be hybridisation. At the moment there are only records of copulation between Rüppell´s and Eurasian Griffon Vultures without any evidence of viable offspring. However, Rüppell’s Vulture has been recorded producing viable offspring with Cape Vulture in South Africa.
We speculate that there is an increased chance of hybridisation in the future as Eurasian Griffon Vulture numbers continue to increase and, if carrying capacity is reached in Iberia, begin to recolonise former breeding areas in Morocco. This effect could produce reverse gene flow issues into the Sahelian populations of critically endangered African Vultures.
Here in The Straits the Rüppell’s Vulture is still considered a rare occurrence, but is encountered with increasing frequency. It has been recorded frequently at feeding stations set up by Fundacíon Migres for Egyptian Vulture conservation projects. This provides a unique opportunity to tag and study the movements of these vagrants and the possibility of reverse gene flow back into African Vulture populations in the Sahel.
On 3rd December 2021 a White-backed Vulture was trapped and it was decided that the concept of understanding the wider conservation issues for declining and critically endangered African Vultures moving through The Straits still holds true for this species. Just as we have seen increases in the occurrence of Rüppell’s Vulture so too could this White-backed Vulture be the forerunner to increased occurrences in North Africa and Southern Europe.
After studying photographs of a White-backed Vulture recently observed and photographed by Javier Elorriaga and Sergio Briones in Tarifa and Los Barrios, we can see that this now-marked bird is not the same individual. This means there are at least two White-backed Vultures on Spanish side of The Straits this year alone with a further two trapped and marked on the Moroccan side this year too.
Understanding these vagrancy patterns potentially linked to declining populations of largely sedentary African Vultures and increases in youth dispersal of Eurasian Griffon Vultures is key to a wider diagnosis of the plight of Africa’s declining Vulture populations.
Implications for conservation
We have considered the implications of this project across our project team and using the framework of spatial targeting for single-species conservation planning (“the Species Recovery Curve”) concluded that more data-gathering was needed to understand the patterns of vagrancy of sub-Saharan African Vulture populations and the subsequent implications for conservation.
Therefore we score the project at Diagnosis 2/3 on the Recovery Curve. This is because whilst we know many of the reasons for decline across the normal range, we still don’t know the full status nor the reasons for their now regular vagrancy into Europe.
Nor do we fully understand vagrant African Vultures interactions with breeding colonies of Eurasian Griffon Vultures once in Europe. There have been observations of Rüppell’s Vultures copulating with Eurasian Griffon Vultures but as yet there is no evidence of viable offspring being produced.
McCarthy (2006) reports numerous instances of White-backed Vulture hybridisation with Rüppell’s Vulture in captivity and unpublished reports of hybridisation with Cape Vulture too. It would therefore seem likely that hybridisation between White-backed and Eurasian Griffon Vultures could be possible.
McCarthy also reports on multiple instances of Rüppell’s Vulture hybridising with Eurasian Griffon Vulture in captivity. An adult specimen in the Natural History Museum, Tring, taken from a nest in Algeria, is considered to be a naturally-occurring wild hybrid between Rüppell’s Vulture and Eurasian Griffon Vulture (Davies & Clark 2018).
Additionally if the occurrence of African Vultures in Southern Europe continues to increase, it is also feasible that they could eventually set up a new intra-specific breeding population.
Main threats to African Vultures
Both primary and secondary poisoning are thought to be key drivers of the rapid decline of African Vultures (including the use of diclofenac in cattle and direct poisoning by poachers using carbofuran). Evidence from wing-tagging and telemetry studies already suggests that annual mortality of present species, principally from incidental poisoning, is perhaps as high as 25%.
Trapping and killing for “traditional voodoo practices” and national and international illegal trade are also threats. African Vulture species are also affected by collisions with power infrastructure, particularly power cables. Longer dry seasons are leading to changes in habitat mosaic and possible lack of food. The loss or felling of nesting trees, and disturbance of nesting trees in particular for White-backed Vultures and at cliff nesting sites for Rüppell’s Vultures also pose problems.
Nesting tree loss and disturbance in places across the Western Sahel is of particular note as there are very few suitable cliff nesting sites for Rüppell’s Vultures (none at all in The Gambia for instance).
As the populations of African Vultures decline further due to these multivariate issues, the motivation towards vagrancy increases, as does the potential for hybridisation and reverse gene flow back to the sub-Saharan African Vulture population.
Hybridisation could therefore emerge as a symptom of overall decline and a new threat to African Vulture populations.
Progress and future work
With the support of IUCN-Med, GREPOM-BirdLife Morocco and the Moroccan Department of Waters and Forests, experts from Spain and Morocco have joined forces to tag vultures with GPS and satellite transmitters.
In northern Morocco, near The Straits of Gibraltar the team worked with Rüppell’s Vulture (Gyps rueppellii) from the Jbel Moussa Vulture Recovery Centre (CRV). 12 birds were tagged with GPS during 2020 (26 trapped and marked with wingtags, 12 of them marked with GPS), and another 12 birds with GPS during 2021 (devices provided by Junta de Andalucía, Fundación Migres, Doñana Biological Station (EBD-CSIC), GREFA (Grupo de Rehabilitación de la Fauna Autóctona y su Hábitat) and Wilder South. Additionally a further two Rüppell’s Vultures have been ringed in Malaga by the University of Malaga.
In early September a young Rüppell’s Vulture in central Portugal was taken into care for rehabilitation and subsequently released after being fitted with a GPS tracker. This Rüppell’s Vulture was named “Vouzela” and tagging was conducted in a collaboration by the Vulture Conservation Foundation (VCF).
Vouzela represents only the third time in Europe and the first time in Portugal that a Rüppell’s Vulture has been fitted with a GPS tag. The question of whether these vagrant African Vultures return to sub-Saharan Africa was subsequently proven this year as Vouzela crossed The Straits of Gibraltar and is now in Northern Senegal.
Did Vouzela originate from colonies in the Sahel or perhaps an unknown intra-specific breeding in Eurasian Griffon Vulture colonies in Iberia?
Increased tagging and monitoring is essential to better understand the movements of declining African Vultures, particularly vagrant individuals, and to ensure we fully diagnose all the potential and multi-variate conservation issues critically endangered African Vultures face as their European congeners’ population continues to increase.
Thanks to the team involved in the projects and collaborations across organisations, we have been able to deploy expertise and resources rapidly, demonstrating the benefits of working collaboratively internationally and at a cross-organisational scale.
This project would not be possible without the financial help kindly received from project sponsors Viking Optical and Doñana Biological Station (EBD-CSIC).
This work would not be possible without the tireless expertise and work of Fundacíon Migres, Doñana Biological Station (EBD-CSIC), GREPOM / Birdlife Morocco, IUCN-Med, Vulture Conservation Foundation (VCF), The Flyway Birding Association / Inglorious Bustards and the Junta de Andalucia.
Simon Tonkin (Inglorious Bustards / Flyway Birding), Carlos Torralvo, Alejandro Onrubia, Cristina Gonzalez (Fundacíon Migres) and Stuart Gillies (Viking Optical)
Davies. R., Clark. B. – African Raptors (2018).
Garrido, J.R., Martín J. and Clavero H. (2020). An overview of the first international symposium on the Rüppell’s Vulture in the Mediterranean region, 24th March 2021. Vulture News, 79: 38-44.
McCarthy. E.M. (2006) – Handbook of Avian Hybrids of the World.
Onrubia, A., Torralvo, C., González, C. and Ferrer, M. (2020). Informe de evaluación de la población del buitre moteado o de Ruppell (Gyps rueppelli) en Andalucía. Consejería de Agricultura, Ganadería, Pesca y Desarrollo Sostenible, Junta de Andalucía: Sevilla. (Unpublished report)
UICN (2021). Recomendaciones para la elaboración de un Plan de acción para la conservación del buitre de Rüppell (Gyps rueppelli) en el mediterráneo occidental. Málaga, España: UICN.