Northern Bald Ibises in Croatia
Newsletter 20/12/2019
As already reported, the start of the autumn migration of our NBIs was delayed this year. On November 22nd, our birds north of the Alps and in Carinthia began to migrate towards south independently. In Carinthia, migration stopped again, probably due to persistent bad weather with fog and poor visibility. But on December 11th, the first day with good flight weather, nine young birds and three adults started from Ferlach in Carinthia and crossed the Loiblpass to Slovenia. Then they headed towards southwest to the coast at Rovinj in Istria. From there they followed the Croatian coastline further south to Zadar.
We hoped that the experienced adults would lead the group back north again, following the right path to the wintering area. Unfortunately, at least three birds - two of them experienced adults - died shortly after arriving in Zadar. Most likely all of them were illegally hunted. We filed a criminal complaint and together with the Croatian police and BIOM-Birdlife Croatia we are currently trying to find the perpetrators. Two members of our team, Corinna Esterer and Alexander Schmied, are on site.
Due to the loss of the two adults, several young birds are now on their own without any chance of reaching the common wintering site in Italy. Corinna and Alexander therefore try to catch these young birds in order to unite them with experienced birds in northern Italy.
This incident in Croatia is very unfortunate, but it also helps us to gain a deeper understanding of the migratory behaviour of the Northern Bald Ibis. We have repeatedly observed that, if possible, the birds follow the straight line towards their destination over long distances. This was initially the case also in this group. After crossing the Loiblpass to Slovenia, they followed the straight line towards the wintering area until they arrived at the sea in Istria.
NBIs usually avoid long flights over open water. Therefore, they had to deviate from the straight line. Various observations suggest that in such situations, birds perceive whether they are still approaching or moving away from the target. This makes it understandable why they did not move north in Istria, as we would expect them to do. It would have increased their distance to the wintering site. Instead, they turned south, which kept the distance to the wintering area the same or reduced it further.
It is exciting that Zadar, where the birds stopped their flight, is the closest point on the Croatian mainland to the wintering area in Tuscany. If the birds continued to fly south along the coast from there, their distance from the wintering area would increase again.
This approach can also be used to conclusively explain several other flight patterns of Northern Bald Ibises, not only in our European population. This is of little help in the current situation in Croatia. However, a deeper understanding of the birds’ migration behaviour enables to further optimize the management in the context of reintroduction and species conservation.
Unfortunately, the current incidents show that illegal bird hunting is a serious threat for biodiversity not only in Italy. Based on our experience, there is little chance to identify the offenders. However, we hope that the criminal complaint and media reports will at least focus attention on this environmental crime. In Italy we have succeeded in doing this. The project and the species are known to the general public and the majority of hunters. As a result, the loss rate due to illegal hunting has decreased significantly during the LIFE project.
Picture: GPS positions of two adult birds “Poncho” and “Donatello”; further data revealed that the whole group of 12 birds reached the Adriatic coast near Rovinj in Istria. From there, they all followed the coastline to Zadar. Both, Rovinj and Zadar are ~ 350 km from the wintering site. From Zadar to the south, this distance increases again.
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