Sea eagle

Taxobox
name = Sea-eagles

---

image_caption = Bald Eagle
("Haliaeetus leucocephalus")
image_width = 300px
regnum = Animalia
phylum = Chordata
classis = Aves
ordo = Falconiformes
familia = Accipitridae
genus = "Haliaeetus"
genus_authority = Savigny, 1809
subdivision_ranks = Species
subdivision = "Haliaeetus leucogaster"
"Haliaeetus sanfordi"
"Haliaeetus vocifer"
"Haliaeetus vociferoides"
"Haliaeetus leucoryphus"
"Haliaeetus albicilla"
"Haliaeetus leucocephalus"
"Haliaeetus pelagicus"

A sea eagle (also called erne or ern) is any of a group of birds of prey in the genus "Haliaeetus" [Etymology: New Latin "sea-eagle", from Ancient Greek [http://archimedes.fas.harvard.edu/cgi-bin/dict?name=lsj&lang=el&word=a%28lia%2fetos&filter=CUTF8 polytonic|ἁλιάετος ("haliaetos") or polytonic|ἁλιαίετος ("haliaietos", poetic variant)] , "sea-eagle, osprey" ("hali-", sea, + "aetos", "eagle"). The two variant Greek forms lie behind the equally correct Latinizations "haliaetus" (as in Pandion haliaetus) and "haliaeetus".] 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.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.] 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.

There are eight living species:
*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.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 [http://www.uni-heidelberg.de/institute/fak14/ipmb/phazb/pubwink/1996/20_1996.pdf PDF fulltext] ] 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.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. [http://www.sil.si.edu/smithsoniancontributions/Paleobiology/pdf_hi/SCtP-0062.pdf PDF Fulltext] (file size 8.1 MB)] The genus was present in the middle Miocene (12-16 mya) with certainty.Lambrecht, K. (1933). "Handbuch der Palaeornithologie". Gebrüder Bornträger, Berlin.]

Their closest relatives are the fishing-eagles in the genus "Ichthyophaga", very similar to the tropical "Haliaeetus" species. 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,Brown, L. H, & Amadon, D. (1968). "Eagles, Hawks and Falcons of the World". Country Life Books, Feltham.] 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.

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.

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.

A 2005 molecular study showed the genus is paraphyletic and subsumes "Ichthyophaga"; the species diverging into a temperate and tropical group. [http://www-personal.umich.edu/~hlerner/LM2005.pdf]

References