Two firsts at once for Antwerp ZOO & Plankendael ZOO. Years of intensive efforts behind the scenes of the black vulture breeding programme paid off in May 2019, resulting in four young vultures. Two are in the nests of their natural parents. A third was placed with an experienced pair. An additional adoptee from a French zoo was then also placed with the same pair. It is the first time that a pair of black vultures has ever adopted two chicks and taken them under their wing at the same time. Scientists from Antwerp ZOO & Plankendael ZOO have also succeeded for the first time in analysing DNA from dried out blood vessels in a hatched egg shell of a black vulture. "This technique offers numerous options for the breeding programme. It is an extra asset as we will now be able to sex chicks much more quickly", explains Marleen Huyghe, studbook keeper and coordinator of the European breeding programme on behalf of our zoos.

BACKGROUND

Over the years, the black vulture has been eradicated throughout Southern Europe, by hunting and poisoning among other things. Together with various conservation organisations, Antwerp ZOO & Plankendael ZOO are working to reintroduce the black vulture to its native distribution area. This means that, a month before fledging, young birds are transported to a release site where they are placed on an artificial nest. They are subsequently monitored from a distance. Young birds play a crucial role in this reintroduction strategy because they become attached to a particular place more easily and stay very true to it. The work does not end with the reintroduction of the birds into such countries as France, Spain and Bulgaria, however. Our research department, the Centre for Research and Conservation (CRC), genetically monitors the reintroduced populations closely, continuously seeking to identify factors that could positively influence the breeding success of breeding pairs in captivity.

HOW EXACTLY DOES THE PROJECT WORK?

Young vultures from zoos are essential to the reintroduction project. As studbook keeper and coordinator of the European breeding programme, therefore, Antwerp ZOO & Plankendael ZOO have been working intensively towards successful breeding, based on their own scientific research, for many years. A first step in this endeavour was to set up a so-called dating aviary in Planckendael ZOO, in 2005, where the vultures can take their time to get to know each other. They are monitored by our researchers and, since 2018, if two birds show signs of really being interested in each other they are both moved to the Breeding Centre at Planckendael ZOO. "Here they can bond more closely as a pair; a basic requirement for successful breeding", explains, Marleen Huyghe, studbook keeper and coordinator of the European breeding programme on behalf of our zoos. "With success it seems this breeding season; three such pairs laid an egg in March 2019."

Black vultures usually only lay one egg. To improve breeding success, you can try to prompt a second lay by removing the first egg soon after it has been laid. This experiment was carried out with one of the breeding pairs. Their first fertilised egg was removed and put in an incubator. One month later the hen laid a second fertilised egg, which hatched on 7 June 2019. The chick from their first egg hatched in the incubator on 7 May 2019. The experts at Antwerp ZOO & Plankendael ZOO chose to place that first chick with the most experienced pair of parents. "The embryo in their egg had died and, pending a possible adoption, the pair had been sitting on a chalk egg to keep them in breeding condition. At that same time, we were contacted by the French zoo Villars-les-Dombes”, Marleen Huyghe continues. "They had also hatched a chick in the incubator, on 2 May 2019. It was their pair's first chick but it could not be placed back with its parents as they were now brooding a replacement chalk egg. So the zoo was looking for suitable adoptive parents within the breeding programme. As we couldn't find a good match we decided to try something unique. For the first time in history, two chicks were placed with one pair of adoptive parents."

The two young first spent a night together in the incubator to get acquainted. Then they were both placed with their adoptive parents. "We had to remove the chalk egg first”, Huyghe continues. "That requires luring the birds away from the nest and they often respond very aggressively. They could possibly vent their aggression on the chicks we put in their nest. But after twenty minutes they began feeding them, and then followed the first attempts to tuck at least one of the chicks 'under their wing'. Tucking them both under at once was too difficult to start with. So they took it in turns. By the end of the day they were able to make themselves wide enough to fit both young under at once." Such a double adoption enables us to breed more chicks a year within the programme, and to brood them naturally. Natural brooding, where the parents raise the chicks themselves, is an important requirement for birds that are to be released. They need to become attached to their own species and not to people. Birds raised by humans become too dependent on them.

"We couldn't find a good match so we decided to try something unique and for the first time in history we placed a second chick with a pair of adoptive parents.”

WHAT IMPACT WILL THE PROJECT HAVE?

The four births and the successful double adoption is another fine reward for the efforts of Antwerp ZOO & Plankendael ZOO and the plan to restore the population of black vultures in Europe. There are various factors to consider when reintroducing birds into the wild. First of all, you must release several young together to ensure there is enough social interaction, otherwise their appetite will reduce. It is also best if they are the same age (ideally there should only be a few days between them) so that they can stay in the artificial nest together for as long as possible. The sex is another issue. There is a surplus of males in the dating aviary at Planckendael ZOO. Being able to sex the birds sooner - well before they are transported to the reintroduction sites - would enable us to ensure a better balance of sexes in the dating aviary.

"In humans, the sex of a foetus can be determined before birth by means of a blood sample taken from the mother. This is not possible for birds because the young develop externally", explains Philippe Helsen, Research Coordinator of Conservation Genetics at Antwerp ZOO & Plankendael ZOO. "Nowadays in the poultry industry, material is collected from the inside of an egg through an opening the size of a needle to determine whether the egg will hatch as a cock or hen. We don't want to go that far with black vultures yet. On the one hand because no manipulation is without risk, and on the other because the thicker egg shell makes it more difficult to trace the blood vessels. But more importantly because, right now, every young vulture counts! We always aim to take any samples non-invasively and not to disturb the parents while brooding. "A saliva sample was taken from the jaw of the French foster chick for DNA analysis. For the first time, the pieces of egg shell in the incubator have also been analysed. "DNA was isolated from dried up blood vessels and the sex was determined”, Helsen continues. "This technique, performed on a black vulture egg for the first time, is an extra asset to the programme." Antwerp ZOO & Plankendael ZOO therefore advises other zoos to send all the egg shells from their incubators to our lab so that we can carry out the special DNA analysis and determine the sex sooner. "That will bring all the expertise together which can only benefit the breeding programme”, Huyghe and Helsen conclude.

"For the first time, we have been able to isolate DNA from dried up blood vessels of a hatched egg, which enabled us to sex the chick. "This technique is an extra asset to the breeding programme."