The osprey-like reversible outer toe: a conspicuous trait in the overlooked morphology of the Grey-headed and Lesser Fish Eagles

The ability to rotate the fourth toe to accompany the first toe in opposition of the second and third toes is well known for the Osprey Pandion haliaetus, as an adaptation to have a stronger grip in catching and carry fish. The presence of a similar ability in the Grey-headed Fish Eagle Haliaeetus ichthyaetus and Lesser Fish Eagle Haliaeetus humilis, not shared with other piscivorous eagles, has largely been overlooked. Based on the growing number of photographs of these birds on the internet, the still scarce literature on their ecology and phylogeny, and personal field observation, I draw attention to this and other traits of their morphology, speculating on their origin and adaptive value.