The word "eagle" is borrowed into English from Anglo-Norman: eagle and Middle French: aigle, both derived ultimately from Latin: aquila ("eagle"). It is cognate with terms such as French: aigle, Portuguese: águia and Spanish: águila.[2] It is broadly synonymous with the less common English term "erne" or "earn", deriving from Middle English: ern, from Old English: earn, in which it acts as the usual word for the bird. The Old English term is turn derived from Proto-Germanic: *arnaz and is cognate with other synonymous words in Germanic languages such as Swedish: örn, German: Aar and Gothic: ara. Through the Proto-Indo-European root, it is further related to words such as ὄρνις ("bird") and Lithuanian: erelis ("eagle"). Although "erne" can be used to refer to any eagle, it is most commonly used for the golden eagle or sea-eagle.[3][4] knotty environments. Hunting techniques differ among the species and genera, with some individual eagles having engaged in quite varied techniques based on their environment and prey at any given time. Most eagles grab prey without landing and take flight with it, so the prey can be carried to a perch and torn apart.[13]
The bald eagle is noted for having flown with the heaviest load verified to be carried by any flying bird, since one eagle flew with a 6.8 kg (15 lb) mule deer fawn.[14][15] However, a few eagles may target prey considerably heavier than themselves; such prey is too heavy to fly with, thus it is either eaten at the site of the kill or taken in pieces back to a perch or nest. Golden and crowned eagles have killed ungulates weighing up to 30 kg (66 lb) and a martial eagle even killed a 37 kg (82 lb) duiker, 7–8 times heavier than the preying eagle.[13][16] Authors on birds David Allen Sibley, Pete Dunne, and Clay Sutton described the behavioral difference between hunting eagles and other birds of prey thus (in this case the bald and golden eagles as compared to other North American raptors):[17] Among the eagles are some of the largest birds of prey: only the condors and some of the Old World vultures are markedly larger. It is regularly debated[according to whom?] which should be considered the largest species of eagle. They could be measured variously in total length, body mass, or wingspan. Different lifestyle needs among various eagles result in variable measurements from species to species. For example, many forest-dwelling eagles, including the very large harpy eagle, have relatively short wingspans, a feature necessary for being able to maneuver in quick, short bursts through densely forested habitats.[13] Eagles in the genus Aquila, found almost exclusively in open country, are noted for their ability to soar, and have relatively long wings for their size.[13]
These lists of the top five eagles are based on weight, length, and wingspan, respectively. Unless otherwise noted by reference, the figures listed are the median reported for each measurement in the guide Raptors of the World[18] in which only measurements that could be personally verified by the authors were listed.[13] Sea eagles or fish eagles take fish as a large part of their diets, either fresh or as carrion.
Proposed subfamily Haliaeetinae. Genera: Haliaeetus, Icthyophaga.
Some authors include Gypohierax angolensis, the "vulturine fish eagle" (also called the palm-nut vulture) in this group.[25] However, genetic analyses indicate it is related to a grouping of Neophron–Gypaetus–Eutriorchis (Egyptian vulture, bearded vulture (lammergeier), and Madagascar serpent eagle).[27]
The fish eagles have a close genetic relationship with Haliastur and Milvus; the whole group is only distantly related to the Buteo group.[27]
Fish eagles exist in every continent throughout the world, except for South America.[28]
Although fish eagles can be found in many different places around the world, they have been classified as "Near Threatened". Reasons such as overfishing, pollution, habitat destruction, and the use of pesticides have contributed to the species' rapid population drop.[29]