Sea eagle
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- This page is about the bird. For other uses, see Sea eagle (disambiguation)
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 Bald Eagle
(Haliaeetus leucocephalus) |
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Haliaeetus leucogaster |
The sea-eagles are a group of 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 second largest eagle native to North America. The White-bellied Sea-eagle can weigh up to 3.4 kg.[2]
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-eagle, 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, Euzbakistan (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,[6][2] 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 showed the genus is paraphyletic and subsumes Ichthyophaga; the species diverging into a temperate and tropical group.[1]
[edit] References
- ^ Etymology: New Latin "sea-eagle", from Ancient Greek halio, the sea + -aetos, "-eagle". The proper Ancient Greek name for sea-eagles was the contracted form Haliaetos.
- ^ a b c d e del Hoyo, J., Elliott, A., & Sargatal, J., eds. (1994). Handbook of the Birds of the World Vol. 2. Lynx Edicions, Barcelona ISBN 84-87334-15-6.
- ^ a b c d Wink, M., Heidrich, P., & Fentzloff, C. (1996). A mtDNA phylogeny of sea eagles (genus Haliaeetus) based on nucleotide sequences of the cytochrome b gene. Biochemical Systematics and Ecology 24: 783-791. doi:10.1016/S0305-1978(96)00049-X PDF fulltext
- ^ Rasmussen, D., Tab, O., Storrs, L., & Simons, E. L. (1987). Fossil Birds from the Oligocene Jebel Qatrani Formation, Fayum Province, Egypt. Smithsonian Contributions to Paleobiology 62: 1-20. PDF Fulltext (file size 8.1 MB)
- ^ Lambrecht, K. (1933). Handbuch der Palaeornithologie. Gebrüder Bornträger, Berlin.
- ^ Brown, L. H, & Amadon, D. (1968). Eagles, Hawks and Falcons of the World. Country Life Books, Feltham.
