The Booted Eagle is one of the most representative raptor species in the Strait of Gibraltar. It is a medium sized raptor of powerful flight whose migration has received low attention by the scientific community. However, this has changed with the recent publication of a comprehensive monograph: “Migration and spatial ecology of the Spanish population of the Booted Eagle” is based on GPS tracking current information. The work has been conducted within the MIGRA project of SEO/Birdlife. It has had the input of a remarkable group of ornithologists from different Spanish institutions. They present the results in a beautifully edited open access document. You can find it in Spanish with an English summary.
Birding The Strait has contributed to this project with several photos of Booted Eagles in migration in the Strait of Gibraltar, including the one on the cover. As ornithologist and birdguides in Tarifa we received this publication with big interest. Next, we summarize some of the most striking results.
Booted Eagle Migration Routes
In Spain the Booted Eagle is a migrant species except in the Balearic Islands, where it is resident. Booted Eagles spend 13% of their lives on migration, 42% at their breeding grounds in Europe and 45% at their wintering quarters in Africa.
All migratory routes converge in the Strait of Gibraltar where the average date of arrival is the 17 of September and the 31st of March in their Southbound and Northbound migrations, respectively. Eagles crossed the Sahara in a broad front following similar routes in spring and summer, with no coastal flyways observed. The studied individuals completed their migration in 28 in spring and 23 days in autumn. Interestingly, this pattern opposes the general trend observed in most migratory species, on which the return migration to their breeding grounds is faster than the autumn migration to the wintering quarters. The eagles flew an average of 8 hours a day, covering from 130 to 250 km, with an absolute record of 541km between two consecutive night roosts!
Visual counts in the Tarifa area have shown that approximately 71% of the individuals belong to the pale morph while 29% belong to the dark one.
The number of Booted Eagles crossing the Strait has significantly increased within the period 1999-2016 with similar numbers at raptor watchpoints in the Pyrenees. Nowadays over 30.000 Booted Eagles cross the Strait of Gibraltar to Africa every year.
The bulk of the Iberian population overwinters in the Western Sahel region including Mauritania, Guinea, Mali, Burkina Faso, Niger, Nigeria, Chad, Cameron and Sierra Leona with a remarkable wintering site fidelity in consecutive years.
The number of Booted Eagles overwintering in Spain is steadily increasing over the last decades. It is a scarce but regular wintering species. We recommend to consult eBird to get further insight on the wintering population of Booted Eagles in Spain.
The logo of a leading energetic corporation on the front cover may arguably raise alarm bells to critical readers. In fact, Iberdrola received a sanction in Spain of millions of euros on account of the electrocution of raptors. This includes the endangered and iconic Spanish Imperial Eagle. Pushing conflicting emotions aside, it is important to highlight that this work identifies and highlights electrocutions and hunting as the two main causes of non-natural mortality for the species.
The global results show the Booted Eagle as a rather plastic species on its foraging, migrating and habitat selection habits. Also, it shows that it has a wide distribution range. Therefore, it seems likely that thanks to this attributes the Booted Eagle will have a more promising future than other less adaptable species. This work stresses the importance of stablishing integrative conservation measurements. For example, the description of breeding sites, foraging areas, migration flyways and wintering regions.
All in all this work fills an important gap on the knowledge of raptor migration. We believe it is of interest for bird enthusiasts, researchers and decision makers.