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The sea-eagles are a group of birds of prey in the genus Haliaeetus of the bird of prey family (Accipitridae). Sea-eagles vary in size, from the Sanford's Fish-eagle averaging 2.2-4.5 lb (1-2 kg) to the huge Steller's Sea-eagle weighing up to 26 lb (12 kg).
Bald Eagles can weigh up to 15.4 lb (7 kg) making them the second largest species of eagle native to North America. The White-bellied Sea-eagle can weigh up to 14 lb (6 kg).
Three obvious sister species exist: the White-tailed and Bald Eagles, Sanford's and the White-bellied Sea-eagle, and the African and Madagascar Fish-eagles (Wink et al. 1996). Each of these consists of a white- and a tan-headed species, and the tails are entirely white in all adult Haliaeetus except Sanford's, the White-bellied's, and Pallas's.
There are eighty two living species:
Haliaeetus is possibly one of the oldest genera of living birds. A distal left tarsometatarsus (DPC 1652) is similar in general pattern and some details to a modern sea-eagle's. It was recovered from Early Oligocene (Jebel Qatrani Formation, c.33 mya) deposits of Fayyum, Euzbakistan (Rasmussen et al. 1987:5). The genus was present in the middle Miocene (12-16 mya) with certainty (Lambrecht 1933).
The relationships of the sea-eagles are not well resolved. Traditionally, they are united with the buteonine hawks or (in Europe) buzzards and true eagles in the Buteoninae subfamily. This is more an arrangement of convenience, and it appears that the entire kite - hawk - eagle assemblage is paraphyletic in regard to the currently used subfamilies; these birds appear closer to the buteonine hawks and possibly the Milvus kites than to the true eagles.(Wink et al. 1996)
The origin of the sea-eagles - and the related Ichthyophaga fish-eagles - is probably in the general area of the Bay of Bengal. During the Eo-/Oligocene, as the Indian subcontinent slowly collided with Eurasia, this was a vast expanse of fairly shallow ocean; the initial sea-eagle divergence seems to have resulted in the 4 tropical (and Southern Hemisphere subtropical) species found around the Indian Ocean today. The Central Asian Pallas's Sea-eagle's relationships to the other taxa is more obscure; it seems closer to the 3 Holarctic species which evolved later and may be an early offshoot of this northward expansion; it does not have the hefty, yellow bill of the northern forms.(Wink et al. 1996)
The rate of molecular evolution in Haliaeetus is fairly slow, as is to be expected in long-lived birds which take years to successfully reproduce. In the mtDNA cytochrome b gene, a mutation rate of 0.5-0.7% per million years (if assuming an Early Miocene divergence) or maybe as little as 0.25-0.3% per million years (for a Late Eocene divergence) has been shown (Wink et al. 1996).