On 3 December 2021, Fundación Migres ringed and GPS-tagged a White-backed Vulture, a rare vagrant to Europe and the first one to be ringed and tagged in Europe.
The occurrence of this species in Iberia – alongside the increased incidence of Rüppell's Vulture in The Straits – is extremely interesting. Both species are Critically Endangered in their regular sub-Saharan range. It is hypothesised that the increase in 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 ‘conveyor belt’ of pre-nuptial Griffon Vulture migration, bringing them north to North Africa and sometimes Europe.
Satellite tagging these vagrant birds will give us new insights into these Critically Endangered species and aid our conservation knowledge for African vultures.
This White-backed Vulture was caught and fitted with a GPS transmitter in southern Spain on 3 December 2021 (Inglorious Bustards).
Background
Since the early 1990s, Rüppell’s Vultures have been encountered in the Iberian Peninsula, particularly around the Straits of Gibraltar.
Following presentations and findings at the IUCN Rüppell’s Vulture symposium and given the increasing occurrence of the species in both southern Europe and North Africa, the project team had aimed to ring and GPS tag this species at a feeding station.
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 Critically Endangered African vulture populations 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 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 African species.
Rüppell’s Vulture is still considered a rare occurrence in the Straits, 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 3 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 an upturn in sightings in North Africa and southern Europe.
A GPS transmitter being fitted to the White-backed Vulture (Inglorious Bustards).
After studying photographs of a White-backed Vulture recently observed and photographed by Javi 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 the Spanish side of the Straits this year alone, with a further two trapped and marked on the Moroccan side in 2021.
Understanding these vagrancy patterns potentially linked to declining populations of largely sedentary African Vultures and increases in youth dispersal of 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 while 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.
We also do not fully understand vagrant African vultures’ interactions with breeding colonies of Griffon Vultures once in Europe. There have been observations of Rüppell’s Vultures copulating with Griffon Vultures but as yet there is no evidence of viable offspring being produced.
Rüppell's Vulture sightings are increasing in Iberia, with one potential threat to the Critically Endangered species being hybridisation with the widespread Griffon Vulture (Tate Lloyd).
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 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 this could eventually lead to 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, as well as national and international illegal trade, are also threats. African vulture species are also affected by collisions with power infrastructure, particularly power lines. 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.
The White-backed Vulture is fitted with a blue ring inscripted '799' on its left leg (Inglorious Bustards).
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 Strait of Gibraltar the team worked with Rüppell's Vulture from the Jbel Moussa Vulture Recovery Centre (CRV). Twelve birds were tagged with GPS during 2020 (26 trapped and marked with wing tags, 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 and is now in northern Senegal.
Did Vouzela originate from colonies in the Sahel or perhaps an unknown intraspecific pair breeding in a Griffon Vulture colony in Iberia? Increased tagging and monitoring is an essential component to answering such questions, and to ensure we fully diagnose all the potential conservation issues these African species face as their European congener’s population continues to increase.
Map showing movements of Rüppell's Vulture 'Vouzela' since release in Portugal in October 2021 (Vulture Conservation Foundation).
Acknowledgements
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.
References
Davies, R, Clark. B. (2018). African Raptors. Helm.
Garrido, J R, Martín, J, & Clavero, H. (2020). An overview of the first international symposium on the Rüppell’s Vulture in the Mediterranean region, 24 March 2021. Vulture News, 79: 38-44.
McCarthy, E M. (2006). Handbook of Avian Hybrids of the World. Oxford University Press.
Onrubia, A, Torralvo, C, González, C, & 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.
