A sea eagle (also called erne or ern, mostly in reference to the White-tailed Eagle) is any of the birds of prey in the genus Haliaeetus^[1] in the bird of prey family Accipitridae.

Sea eagles vary in size, from the Sanford's Fish Eagle averaging 2–2.7 kg to the huge Steller's Sea Eagle weighing up to 9 kg.^[2] At up to 6.9 kg, the White-tailed Eagle is the largest eagle in Europe. Bald Eagles can weigh up to 6.3 kg, making them the largest eagle native to North America. The White-bellied Sea Eagle can weigh up to 3.4 kg.^[2] Their diets consist mainly of fish and small mammals.

There are eight living species:^[2]

• White-bellied Sea Eagle (H. leucogaster)
• Sanford's Sea Eagle (H. sanfordi)
• African Fish Eagle (H. vocifer)
• Madagascar Fish Eagle (H. vociferoides)
• Pallas's Fish Eagle (H. leucoryphus)
• White-tailed Eagle (H. albicilla)
• Bald Eagle (H. leucocephalus)
• Steller's Sea Eagle (H. pelagicus)

Three obvious species pairs exist: White-tailed and Bald Eagles, Sanford's and White-bellied Sea Eagles, and the African and Madagascar Fish Eagles.^[3] 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, White-bellied, and Pallas's.

Haliaeetus is possibly one of the oldest genera of living birds. A distal left tarsometatarsus (DPC 1652) recovered from early Oligocene deposits of Fayyum, Egypt (Jebel Qatrani Formation, c.33 mya) is similar in general pattern and some details to that of a modern sea-eagle.^[4] The genus was present in the middle Miocene (12-16 mya) with certainty.^[5]

Their closest relatives are the fishing-eagles in the genus Ichthyophaga, very similar to the tropical Haliaeetus species.^[2] The relationships to other genera in the family are less clear; they have long been considered closer to the genus Milvus (kites) than to the true eagles in the genus Aquila on the basis of their morphology and display behaviour,^[2][6] more recent genetic evidence agrees with this, but points to them being related to the genus Buteo (buzzards) as well, a relationship not previously thought close.^[3]

The origin of the sea eagles and fishing-eagles is probably in the general area of the Bay of Bengal. During the Eocene/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 four 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 three 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, retaining a smaller darker beak like the tropical species.^[3]

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.^[3]

A 2005 molecular study found that the genus is paraphyletic and subsumes Ichthyophaga, the species diverging into a temperate and tropical group.^[7]

Webcams

Nesting pairs of both the Bald Eagle and White-bellied Sea Eagle have been subject to live streaming web cam footage.^[8][9]

References

Sources

• del Hoyo, J.; Elliott, A.; Sargatal, J., eds. (1994). Handbook of the Birds of the World. 2. Barcelona: Lynx Edicions. ISBN 84-87334-15-6. 
• Wink, M.; Heidrich, P.; Fentzloff, C. (1996). "A mtDNA phylogeny of sea eagles (genus Haliaeetus) based on nucleotide sequences of the cytochrome b gene" (PDF). Biochemical Systematics and Ecology 24 (7–8): 783–791. doi:10.1016/S0305-1978(96)00049-X. http://www.uni-heidelberg.de/institute/fak14/ipmb/phazb/pubwink/1996/20_1996.pdf.  edit