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Lesser spotted eagle conservation success depends on youngsters following migrating adults

The Company of Biologists

As the lesser spotted eagle is listed as endangered in Germany, Bernd-Ulrich Meyburg from BirdLife Germany (NABU) knows that the graceful bird of prey's future is far from assured in his home country. Meyburg explains that the German population has dwindled to just 110 breeding pairs in recent decades, largely due to habitat loss and persecution by poachers during their long migration to their overwintering sites in southern Africa. In a bid to stem the destruction of the German population, Meyburg has relocated 50 chicks from the more stable Latvian population some 940 km to the northeast in the hope of boosting the declining German numbers. However, it was not clear whether the translocated chicks would survive the gruelling migration to their overwintering sites in southern Africa and return to Germany instead of Lativa. In a paper published in Journal of Experimental Biology at http://jeb.biologists.org, Meyburg and his colleagues show that the translocated Latvian chicks are capable of returning successfully from South Africa, all be in it in small numbers, offering the hope that the German population can be rescued.

'I initiated the conservation project in the federal state of Brandenburg in 2004', says Meyburg, explaining that the scheme has not impacted the Latvian population, as he takes only the chicks that hatch second, which usually die within a matter of days. Meyburg and his international team of conservationists rescued the chicks -- referred to as 'Abels', after the biblical story of Cain and Abel -- even before they had hatched and reared them in Latvia, before relocating them to a secure hide -- known as a hack -- in the Schorfheide-Chorin reserve in Brandenburg. 'The small chicks are fed using a puppet that looks like the head of an adult bird', says Meyburg, adding, 'Once they are big enough to feed on their own, the food is introduced into the hacking chamber through a small hole in one of the solid walls ... to avoid imprinting on humans'.

Then, in 2009, the team fitted lightweight GPS transmitters to 12 Latvian Abels, eight lesser spotted eagle youngsters from nearby nests and nine adults to track their departures and migrations. Meyburg recalls that the majority of the Abels embarked on their migration earlier than the other migrants, departing between 10 and 11 September, with a few remaining until 16-17 September. In contrast, most of the adults set off between 16 and 19 September, with the Brandenburg-hatched chicks departing between 14 and 16 September -- although one lingered until 26 September, when the final adult departed. However, when Meyburg analysed the bird's migrations, he realised that the Abels' early departure probably spelled disaster.

Instead of following the route taken by the more experienced adults -- southeast across the Bosphorus and along the Eastern Mediterranean coast before entering Africa at Suez - most of the Abels struck out west before attempting to cross the Mediterranean. Meyburg explains that as eagles are large compared with many other migrants, they cannot sustain flapping flight and depend instead on thermals generated above land to remain airborne; without the benefit of lift-generating thermals, the inexperienced birds were doomed to fail as they crossed the water. Consequently, four of the youngsters perished in the Mediterranean and two died in North Africa, with only four completing the full migration.

In contrast, just one of the eight youngsters that had hatched in Germany died on the outbound journey, following the same route as the experienced adults south across the Bosphorus. 'Juvenile lesser spotted eagles are highly dependent on adult guidance in order to survive their first migration and locate the traditional winter grounds', says Meyburg.

Although it was clear that the epic round trip took a significant toll on all of the youngsters -- only two of the 12 2009 Abels returned, while just 25% of the German chicks made it home -- Meyburg is excited by the potential of the Abel conservation strategy. 'The greatest success was a Latvian male, which returned at the age of 2 years to the release site and fed there a few times', recalls Meyburg, adding that the youngster eventually reared his own chick near the site 3 years later. 'A new territory had been established which did not exist before', he says triumphantly.

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IF REPORTING THIS STORY, PLEASE MENTION JOURNAL OF EXPERIMENTAL BIOLOGY AS THE SOURCE AND, IF REPORTING ONLINE, PLEASE CARRY A LINK TO: http://jeb.biologists.org/content/220/15/2765.abstract

REFERENCE: Meyburg, B.-U., Bergmanis, U., Langgemach, T., Graszynski, K., Hinz, A., Bo?rner, I., Meyburg, C. and Vansteelant,W. M. G. (2017). Orientation of native versus translocated juvenile lesser spotted eagles (Clanga pomarina) on the first autumn migration. J. Exp. Biol. 220, 2765-2776.

DOI: 10.1242/jeb.148932

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