It is a widespread summer visitor to Iberia, breeding in open woodland throughout Portugal apart from in the north-west and the extreme south-west. A few birds overwinter in the Algarve and the Tagus and Sado river systems but most return to Africa in the autumn. Satellite tracking has revealed that Iberian birds all go to West Africa, from Mauretania to Nigeria.
Like most large raptors reliant on thermals to gain height, Booted Eagles are averse to long sea crossings. Their migration results in large concentrations at the principal crossing point, the Straits of Gibraltar, but numbers also congregate in the Cape St. Vincent area before aborting at ‘land’s end’ and heading back to the east. Flocks of thirty or forty are not unusual here in September/October. The return passage in spring is less evident but I did see a flock of almost thirty near Burgau in late March this year, which had probably made the direct crossing from Morocco.
Confusingly, the Booted Eagle comes in two colour forms. The commoner pale phase (pictured) is one of the easiest large birds of prey to identify, with its unique black-and-white underwing pattern. The uniform brown dark phase is trickier and could be confused with Black Kite, Honey Buzzard, Marsh Harrier or a juvenile Bonelli’s Eagle. Familiarity with the wing shape, tail length and flight modes helps!
Doves are a favourite prey of Booted Eagle, which is a swift and agile hunter. In towns and villages they may even be snatched from rooftops. Mammals up to the size of rabbits are also taken, as well as large lizards. Their versatility is the foundation for their success in a competitive and changing environment. Iberian populations have increased, to perhaps around a thousand pairs in Portugal. Global warming may be partly responsible for recent northerly extensions of range.
The species is the most vocal of the eagles in the breeding season. A shrill but melodious ‘kli-kli-kli is the most commonly used call but several ‘variations on a theme’ are delivered during elaborate sky-dance song flights. Their nests are almost always high up in a tree and are often reused in successive years. The sites are defended aggressively against intruders.