Testing different release techniques of captive-bred Egyptian vultures in Bulgaria

Young captive bred Egyptian vulture sitting on a grassy area
Captive bred Egyptian vulture in released into the wild

The Balkan population of the globally endangered Egyptian vulture is in decline. The majority of Europe´s Egyptian vultures are on the Iberian peninsula, but the 40 pairs found in the Balkans are a vital bridge between the Asian and Iberian populations. Boosting existing populations with individuals from captive-breeding, or reintroduction in areas where the species already went extinct, is potentially a valuable conservation tool. However, there are several questions that remain to be answered about releasing captive-bred individuals of this species which the Egyptian Vulture New LIFE project aims to better understand. 

 

Migratory vultures

Egyptian vultures are the only one of Europe’s four vulture species that undertake long migrations to warmer overwintering grounds. When captive-bred individuals are released they often undertake their long migration without the presence of other members of their species, specially adult birds, that tend to migrate early. 

 

In 2016 three captive-bred Egyptian vultures were released in Bulgaria as part of a trial that had mixed results - one bird survived well, but unfortunately two died at sea during migration. Whilst this mortality on migration was also reported in tagged wild-born individuals, it could constitute a problem for this declining population. 

 

Testing different release techniques

 As part of the Egyptian Vulture New LIFE project, we at the Vulture Conservation Foundation are supporting and contributing to a more comprehensive experiment that aims to test the  different techniques of releasing captive-bred birds. This project will measure relative survival of birds released under three different techniques and identify and fine-tune the best technique for conservation restocking or reintroduction at later stages. In this experiment at least 10 captive-bred individuals will be released in each of three methods. 

 

Fostering of chicks 

Two captive-bred Egyptian vulture chicks, bred in Prague Zoo (see photos below), have been transported to Bulgaria and today they will be put on wild nests, to be adopted by wild pairs. Once placed in the nest the progress of the chicks will be closely monitored by Bulgarian Society for the Protection of Birds staff and should any complications occur they will intervene to protect the chick/nesting pair.  

We will bring you news of these birds in the coming months. 

 

Delayed release

The second technique that is being tested and monitored as part of the project is delayed release. Back in December four captive-bred birds from zoos in Schonnbrunn (Austria), Prague (Czech Republic) and Jerez (Spain), that hatched back in the 2017 breeding season, were transported to Bulgaria and put in an acclimatisation aviary in Bulgaria’s Eastern Rhodopes mountains, next to a supplementary feeding point, in an area where wild Egyptian vultures occur. These one-year old birds were released in mid-May and since then have been behaving normally.

Four young Egyptian vultures perching on a ledge in an acclimatisation aviary
Egyptian vultures in the acclimatisation aviary

Thanks to the GPS transmitters that were fitted to the birds our colleagues at the BSPB have been able to monitor their flights and Polya, Akaga, Boyana and Pantaley-Jerez have been traveling confidently around the Eastern Rhodopes. 

 

Initially after their release the four birds stayed near the acclimatisation aviary exploring the area and feeding at the feeding stations as you can see Boyana doing here:

Of the four the most adventurous seems to be Akaga who was the first to leave the area and traveled an astonishing 200km over two days. The team used the GPS data and created a 3D visualisation of her movements during that exploration

 

After her travels Akaga returned to the area and was observed joining the other birds released at a feeding station. 

Release of captive-bred birds usually takes place once they are of fledging age, but delaying their release until the next spring aims to allow birds to meet other wild members of their species, learn how to use the area and foraging, and be in better state of fitness in order to undertake the long migration south to Africa to overwinter when the summer comes.

 

Hacking method

The more traditional technique being used to release captive-bred Egyptian vultures in Bulgaria is the hacking method. Two chicks will be taken to Bulgaria in the coming months and will be released in artificial enclosed surrogate nest where they will be fed (without any human contact) and looked after from a monitoring point in the distance until they fledge.

 

All birds released will be fitted with the same GPS transmitters to help our colleagues in the BSPB to monitor their survival, migration and help us measure the success of the three different techniques. 

 

A version of this news item appeared on the Egyptian Vulture New LIFE website. 

 

 

 

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