Genus of birds
A sea eagle or fish eagle (also called erne or ern, mostly in reference to the white-tailed eagle) is any of the birds of prey in the subfamily Haliaeetinae of the bird of prey family Accipitridae. Ten extant species exist, currently described with this label.
The subfamily has a significant reach, with a scholarly article in 2005 reporting that they were "found in riverine and coastal habitat[s] throughout the world". However, "Haliaeetinae" inhabited areas have experienced particular threats given the context of human impacts on the environment.
Taxonomy and evolution.
The genus "Haliaeetus" was introduced in 1809 by French naturalist Marie Jules César Savigny in his chapter on birds in the "Description de l'Égypte". The two fish eagles in the genus "Ichthyophaga" were found to lie within "Haliaeetus" in a genetic study in 2005. They were then moved accordingly. They are very similar to the tropical "Haliaeetus" species. A prehistoric (i.e. extinct before 1500) form from Maui in the Hawaiian Islands may represent a species or subspecies in this genus.
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; more recent genetic evidence agrees with this, but points to their being related to the genus "Buteo" (buzzards/hawks), as well, a relationship not previously thought close.
A 2005 molecular study found that the genus is paraphyletic and subsumes "Ichthyophaga", the species diverging into a temperate and tropical group.
Evolution.
"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, about 33 million years ago (Mya)) is similar in general pattern and some details to that of a modern sea eagle. The genus was present in the middle Miocene (12–16 Mya) with certainty.
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 living 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.
Issues in the modern era.
The "Haliaeetinae" subfamily is an especially threatened collection of creatures within the broader "Accipitridae" species, according to the academic journal "Molecular Phylogenetics and Evolution", given the "anthropogenic factors" involved. The publication reported in 2005 that prior trends had meant that sea eagles could be "found in riverine and coastal habitat[s] throughout the world". In terms of international scientific campaigns, the Convention on International Trade in Endangered Species (CITES) protects all entities in the broader species, including sea eagles.
Description.
Sea eagles vary in size, from Sanford's sea eagle, averaging , to Steller's sea eagle, weighing up to . At up to , the white-tailed eagle is the largest eagle in Europe. Bald eagles can weigh up to , making them the largest eagle native to North America. There are exceptional records of even heavier individuals in both the white-tailed and bald eagles, although not surpassing the largest Steller's sea eagles. The white-bellied sea eagle can weigh up to . They are generally overall brown (from rich brown to dull grey-brown), often with white to the head, tail or underparts. Some of the species have an all-yellow beak as adults, which is unusual among eagles.
Their diets consist mainly of fish, aquatic birds, and small mammals. Nests are typically very large and positioned in a tree, but sometimes on a cliff.
The tail is entirely white in adult "Haliaeetus" species except for Sanford's, white-bellied, and Pallas's. Three species pairs exist: white-tailed and bald eagles, Sanford's and white-bellied sea eagles, and the African and Madagascar fish eagles, each of these consists of a white- and a tan-headed species.
References.
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