| Sea-eagles | |
|---|---|
| Bald Eagle (Haliaeetus leucocephalus) |
|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Falconiformes (or Accipitriformes, q.v.) |
| Family: | Accipitridae |
| Genus: | Haliaeetus Savigny, 1809 |
| Species | |
|
Haliaeetus leucogaster |
|
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]
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]
Nesting pairs of both the Bald Eagle and White-bellied Sea Eagle have been subject to live streaming web cam footage.[8][9]