Summary maps (2021)

In June 2021, GPS-GSM transmitters were deployed on 11 adults and 4 juveniles just before they leave their colony in Lastovo Archipelago (Croatia) by Sven Kapelj and its team from Udruga BIOM. These transmitters allow detailed live tracking without the need for recapture, and falls naturally from the bird after a few weeks of tracking.

Some individuals traveled over 2500 km to reach the pelagic waters of the Black Sea.
Others have so far limited their flights to the northern / central Adriatic. Two individuals appeared to engage into migration towards the Black Sea, but the tracking signals stopped close to Sporades Islands and near the Gulf of Patras, respectively.

16.09.21Concluding remarks 

Reality check:  the initial phase of our Yelkouan program is now drawing to a close … due to the natural ‘death’ of our transmitters which survived anyway much beyond our wildest expectations.

Here are some key findings that clearly make a success of our eleven-week investigation.  Some were totally unsuspected. 

We have identified for the first time a seasonal axis of connectivity between the Adriatic and Black seas via a seabird species that leaves its nest in the central Mediterranean to travel as far as the northeastern corner of the Black Sea.  The migratory flights of our tagged individuals were all distinct in time (asynchronous) but very similar in their trajectories, with the added discovery that they never flew overland, even avoiding the major shortcut offered by the Canal of Corinth.  What are their main navigational tools ?  The triggers for their individual departure ?

Expending such massive energetic costs (flying over 3,000 km a few meters above the waves !) is more than compensated by reaching the spawning grounds for millions of anchovies – the main staple food of the Shearwater – near the Azov Sea.

The individuals found migrating in our study did not exclude juveniles, born a few weeks previously.  Are they travelling with parents ?  With other elders ?  With other juveniles?  Other individuals studied were still flying in the north Adriatic when we lost, one by one, their signal.  Distinct migration strategies ? Or just a delay in taking off for the Black Sea?

Thousands of Yelkouan Shearwaters gathering in the Black Sea, east of the Strait of Kerch
(photo: A. V. Popovich)