Monday 2 September 2013


Booted Eagle (Aquila pennata). Valiente, male (photo: Domingo Rivera).

In 2011 the MIGRA project of SEO/BirdLife started, dedicated to the study of the migration of birds from Spain and using, amongst other methods, satellite transmitters to track the movements of many individual birds. One of the first species involved was Booted Eagle (Aquila pennata), with 15 tagged individuals up to 2013 from various parts of Spain, including four from Extremadura, as part of a project led by the Government of Extremadura. In 2011 six birds were tracked and in 2013 it was eleven, now only ten because of the first tagged birds, a male called Valiente, was found dead, hit by a vehicle, a few weeks ago. The peculiarities of the first journey taken by Luna and Valiente, the first Booted Eagles from Extremadura that were tagged in 2011, were described before in this blog ( autumn journey and winter and spring return) and so we will not repeat the details.

Valiente was an adult male dark morph Booted Eagle tagged at La Roca de la Sierra, Badajoz on 3rd August 2011 and whose transmitter continued to show his location until 4th August 2013, two years and a day later, when he was killed on a road between orchards in Valdelacalzada, Badajoz. A cyclist discovered the corpse and was surprised to find it was ringed and carried a yellow apparatus on its back, which he removed and returned. Domingo Rivera and Ángel Sánchez told us of his breeding history over the last three years. In 2011 Valiente successfully raised on his own a chick, as his mate had died on a wire when the chick was only a week old. In 2012, he took over a Raven’s nest in a eucalyptus tree, paired with a pale phase female and despite building a further two nests failed to breed. In 2013, he failed to pair and travelled in an erratic fashion over the area where he normally bred. With respect to his migrations, the map above shows the journeys in 2011/12 and 2012/13, very similar to each other. In both cases, he wintered in the same general area: once in Niger and the other time in Nigeria. The two-way journeys across the Sahara showed that the return journey was always to the west of the route taken in the outward journey. As can be seen in the graph below, the dates did not vary much, the 2012 journey was a bit earlier than 2011 and he spent more time in 2012 on his wintering grounds in Niger. The return journeys were almost identical in terms of dates and duration. Compared with other tagged Booted Eagles, Valiente had been unusual, being the only one with two wintering zones, one that had wintered further away (3,500 km) and the fastest in its return journeys. Of the four tagged birds from Extremadura, he was the only one that wintered in the eastern Sahel, the others staying much further to the west, between Mali and Mauritania.

Luna is an adult female dark morph, tagged in Alburquerque (Badajoz) on 3rd August 2011 and whose transmitter continues in operation. Domingo Rivera and Ángel Sánchez again describe her breeding history over the last three years. In 2011, she raised two chicks in a nest in a eucalyptus tree. In 2012, she occupied the same nest, but following its collapse because of weather conditions, she did not raise any young. In 2013, she moved to a new nest in a cork oak where again she raised two chicks. With respect to migration, the map shows the journeys made in 2011/12 and 2012/13. In both cases, she wintered in the same zone between Mali and Mauritania, some 2,500 km from the nest site, and, as with Valiente, the outward journey was more eastern than the return. In the graph below, the most interesting is that the departure date was much earlier in 2012 (5th August, a month earlier than usual). This was not seen with the other 15 tagged birds and in principle could have been explained by the breeding failure that year. However, that may not have been the reason, because in 2013, Luna also departed very early (2nd August) despite having a successful season. The return in 2013 was also earlier than in 2012, but by only a week.

The other two Booted Eagles from Extremadura that have been followed are a pair and they breed in the municipality of Badajoz, their names are Guadiana (male) and Alqueva (female). Both are pale morphs and in general their migratory behaviour has been similar to that of Luna, apart from the departure dates, with similar routes and wintering areas in the western Sahel (Mali and Mauritania).