Everything you wanted to know on the Booted Eagle migration and never dared to ask!

Dark morph Booted Eagle reaching Europe from Africa across the Strait of Gibraltar.

The Booted Eagle is one of the most representative species of the raptor migration in the Strait of Gibraltar. It is a medium sized raptor of powerful flight whose migration has received low attention by the scientific community. This has changed, however, with the recent publication of a comprehensive monograph on the “Migration and spatial ecology of the Spanish population of the Booted Eagle” based on GPS tracking. The work has been conducted within the MIGRA project of SEO/Birdlife and has had the input of a remarkable group of ornithologists from different Spanish institutions. The results have been presented in a beautifully edited open access document in Spanish with English summary.

Booted Eagle in active migration over the ocean in Tarifa.

Birding The Strait has contributed to this project with several photos of Booted Eagles on migration in the Strait of Gibraltar, including the one in the cover. As ornithologist and birdguides in Tarifa we have received this publication with big interest and next we summarize some of the most striking results:

Pale morph Booted Eagle over Tarifa in southbound migration to Africa.

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% in their breeding grounds in Europe and 45% on 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!

Dark morph Booted Eagle in the Strait of Gibraltar.

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 and a similar result has been obtained 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.

Pale morph Booted Eagle in Tarifa.

The number of Booted Eagles overwintering in Spain is steadily increasing over the last decades and nowadays it should be considered a scarce but regular wintering species. We recommend to consult eBird to get further insight on the wintering population of Booted Eagles in Spain.

Juvenile pale morph Booted Eagle perched in a powerline which has been isolated to avoid raptor electrocution in La Janda, the Strait of Gibraltar.

The logo of a leading energetic corporation on the front cover may arguably raise alarm bells to critical readers. In fact, Iberdrola has been sanctioned with millionaire euro fines in Spain on account of the electrocution of raptors, including the endangered 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.

Pale morph Booted Eagle in active migration in the Strait of Gibraltar.

The global results show the Booted Eagle as a rather plastic species on its foraging, migrating and habitat selection habits with a wide distribution range. It seems likely therefore 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 including its breeding sites, foraging areas, migration flyways and wintering regions.

Booted Eagle near Tarifa
Booted Eagle in active migration near Tarifa

All in all this work fills an important gap on the knowledge of raptor migration and it is of interest for bird enthusiasts, researchers and decision makers.