The LIFE+ Project "Conservation of Imperial Eagle and Saker Falcon in key Natura 2000 sites in Bulgaria" (Save the Raptors) is the largest program so far for satellite tracking of wild birds in Bulgaria, and is one of the largest such programs in Europe.
The BSPB has tagged 25 juvenile Imperial eagles with satellite tracking transmitter in five years. The objective is to learn more about their way of life, where they roam, where they winter, their migration periods and, mainly, the threats they face during the first years of their lives. Four years later we have thousands of records from the transmitters on those 25 birds and they have shown us in almost real time and with exceptional precision the birds' most important places, the routes and migration periods, the temporary swarming sites and, also, the areas where the juvenile eagles spend the winter and the summer. The most significant result from satellite tracking, however, are the causes of premature death of most of the marked eagles - some of these causes were completely unexpected and new for the experts, while others, although presumable, proved extremely deadly and widespread among the Bulgarian population of the species.
What is satellite tracking?
The satellite tracking transmitters allowed the BSPB experts to follow the flight of the eagles and to collect and analyze information about the threats facing this globally endangered species and the reason for reduction of its population.
The transmitters are fitted on the juvenile birds when they are 55-60 days old, shortly before they leave their nests. Then they are sufficiently large and strong – as large as an adult eagle, but still unable to fly. The transmitter is a small device with a GPS receiver and transmitter, with an antenna, and is attached to the back of the bird with special Teflon straps. It is only 70 grams in weight (less than 3% of the individual's weight); so that the bird becomes fully accustomed to it and can carry it until the end of its life. The device has a solar panel which recharges the battery with energy from the sun and, thus, has an extremely long life. Placing the transmitter on the back of the bird is extremely important - it must not interfere with the bird's normal life. This is why the BSPB uses the methods of the best European experts in satellite telemetry and tagging.
Each one of us may become part of the eagles' life and may trace their flights in almost real time using the interactive satellite tracking module. Individual birds are noted with their name and identification number, and their flights are designated with different colors on the map.
See a video of satellite transmitter tagging here.
The stories of the Imperial eaglets
Now that we have started tracking the juvenile birds with the latest equipment for satellite telemetry, we, humans, know the biographies and personal destinies of each Imperial eagle with a transmitter.
The eaglet Perun, photographed while BSPB experts were tagging it with a transmitter in 2009, has become the symbol of Imperial eagle conservation. Its stern and majestic stare adorns many awareness materials of the BSPB. Unfortunately, his fate was tragic - he died shortly after his first flight by electrocution when he perched on a hazardous grid pole only 4 km away from his nest. He is the first proven victim of electrocution in Bulgaria after satellite tracking was initiated by the BSPB. Today, the pylons around its nest are safeguarded and we hope that the eagles from the new aerie of his parents will fare better.
The eaglet Perun, photography: Svetoslav Spasov
Stancho was hatched in Sakar in 2010. He went on a long journey to the south and reached the Sudan – the southernmost point reached so far by one of our transmitter-wearing eagles. It is interesting to note that while Stancho was roaming around Eastern Africa, his sister, Burya, spent the winter in Bulgaria and flew during the next year to one of the northernmost points reached by Imperial eagles from Bulgaria - the Central Belarus. Stancho's story is full of mystery. Perhaps he was killed or poisoned by local people, because his transmitter emitted signals from a sheep pen of local shepherds for several weeks, and then stopped. A month later a single signal was emitted from Khartoum, Sudan's capital city. Then the BSPB contacted the Sudan Wildlife Society and asked them to organize a trip to find data about Stancho. Unfortunately, only feathers were found and the transmitter had disappeared.
The eaglet Dora, hatched in 2009, was found lifeless a year later by shepherds in European Turkey. On seeing the transmitter on the back of the bird, they had decided that this is some military technology. The shepherds called the gendarmes who contacted the Turkish Ministry of Environment and transferred the bird for analysis in a Turkish university. The autopsy found out that the death was caused by a heart infection which may be the result of poisoning. More than 20 dead Common buzzards have been found in the same region of Turkey at the same time.
One of the most interesting lots is that of Naiden, an eagled hatched in 2011. Even before he had learned to fly, its nest fell during a storm. BSPB volunteers started searching for the eagled and found it a few days later some 400 m away from the nest. They constructed an artificial nest on a neighboring tree and fed the eagled with pork chops, marked it with a satellite transmitter and placed him in the new nest. After a few days of hesitation, his parents took him back and raised him - fed him and took care of the juvenile bird. Naiden left his nest successfully, but two months later he was found without one leg and with advanced necrosis of the other leg, caused by electrocution. The eaglet tore the dead tissue of his leg himself. The bird was sent urgently to the Wild Animal Rescue Centre of the Green Balkans in Stara Zagora, but, unfortunately, the experts there could not save it.
Niko is the first Imperial eagle marked with a satellite transmitter in 2008 (prior to the LIFE+ project). He wintered in Southern Israel and in the Gaza Strip during the conflict and the fights in 2008-2009, and survived. Then the bird returned to Bulgaria and went to Northern Ukraine. His last signal came in January 2010 from near Dimitrovgrad. His fate remains unknown, despite multiple searches by the BSPB for his remains or his transmitter.
The eaglet Sofia, hatched in 2009, is one of the longest surviving birds. She spent two consecutive winters in Western Syria. In the summer, she roams for a long time around the towns of Sliven and Plovdiv. She has been discovered overnighting on one of the hills in the town and frequently flies over the town to hunt around the ring road. She died in June 2011 poisoned by a bait placed by pigeon breeders near the town of Perushtitsa.
At present, two of all 22 birds with transmitters are alive and sending signals. Darik II, for whom this is the third winter, is no longer migrating to the south but roams within Bulgaria and in the Odrin area. The other eagle, Pesho, hatched in 2012, winters in Turkey, between Istanbul and the capital city of Ankara.
Eight of the young Imperial eagles, or 80% of the birds whose destiny is known to us, have died by electrocution when perching on hazardous poles of the power distribution network. Prior to satellite tracking, the experts assumed that there are eagles killed by electric shock, but no one believed that electricity kills so many Imperial eagles.
Two of the eagles were poisoned by illegal bait, and the fate of 10 of the tagged birds remains unknown. Their transmitters simply stopped emitting signals - it is possible that some of these eagles may have died by various causes, such as being shot by poachers, or have been killed by electricity which also has damaged the transmitters. In such cases, is impossible to find out anything about the fate of these birds.
It is very likely that some of the birds may still be alive but with damaged transmitters or perhaps they have managed to take them off, as is most likely the case of the eagle Burya whose transmitter was found with disintegrated stitches, and no trace of the bird has been found. We hope that some of the birds are alive and that we may see them nesting in a newly formed pair.
The wonder of migration
Similar to many other birds nesting in Bulgaria, most juvenile Imperial eagles also winter to the south of our latitude. This is a little known fact, perhaps because the adult birds remain here permanently and do not migrate. They are more experienced hunters and succeed in finding food even in the hard months of the winter, when hedgehogs and sousliks hibernate. However, the youngsters prefer travelling several thousand kilometers to the south in search of more abundant food.
Most young Imperial eagles which hatch in Bulgaria spend the winter in Turkey or in the Middle East. Two of the eagles - Stancho and Boril, have reached the Sudan and Saudi Arabia, the southernmost points reached by our tracked eagles. Still, some eagles winter in Bulgaria as well, which shows that their survival behavior and strategy are far more complex and unpredictable than those of the typical migrating species which always spend the winter in the Tropics.
The migration routes of the young eagles are now far better known, as a result of the tracking of these 22 birds with satellite transmitters. Modern telemetry has allowed us to find out the main routes preferred by the eagles. Frequently, they travel more than 200 km in a day. We know where the birds usually stop for rest and where juvenile Imperial eagles congregate in large groups. This has been confirmed by visual observation and photographs of our Imperial eagles with transmitters.
Photo of Saci in Turkey, Ogus Altun
Satellite tracking has given us extremely valuable data about the conservation of this globally threatened species and has proven the need for comprehensive measures and trans-boundary cooperation for the preservation of the Imperial eagle. It is for this reason that the BSPB has worked extremely actively with our colleagues from Doga Dernegi - BirdLife Turkey, and has been expanding its efforts to protect the species outside its nesting territories in Bulgaria.
Satellite tracking has given us valuable information about the roaming of juvenile birds in other directions as well, not only to the south. Niko, the first tagged eagle, has reached the most northern part of the Ukraine, and Burya, the female eagle, went as far as Belarus - the most northern point reached by any of our eagles. Drago roamed near the Polish town of Kraków, but then went to winter in South-Eastern Turkey. Shatsi and Topola spent a summer in Dobrudja, Bulgaria, where they had found suitable habitats and sufficient food.
Dangerous poles, poisons, and poachers
The invaluable information collected by satellite tracking has given us far more knowledge of the life of Imperial eagles and of the reasons for the small size of their population. The satellite telemetry data are rather startling. Only 2 of the 22 tracked birds are alive presently. The others have died by electrocution, by poison baiting for predators or placed by pigeon breeders who aim to eliminate raptors, and by being shot by poachers.
To counteract these proven threats, the BSPB has increased the measures and its efforts in these fields of key importance for the conservation of the species. Approximately BGN 100,000 have been invested for safeguarding of the most dangerous electricity poles in the areas inhabited by Imperial eagles during the LIFE+ project “Save the Raptors”.
To combat the use of illegal poison and poaching, the BSPB has worked actively with all governmental institutions - the Police, the Prosecutor's Office, the Ministry of Environment and Waters, the local authorities, the Union of Hunters and Fishermen in Bulgaria, and many other concerned organizations. Much effort is being made to inform and train key local communities - farmers, hunters, schoolchildren and many others.