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Eagles in the Environment

Eagles in the environment Eagles in the environment (c) Kjartan Trana

Eagles are top avian predators in the ecosystems they inhabit. White-tailed Sea Eagles are one of a group of related eagles within the genus Haliaeetus comprised of eight distinct species. The Haliaeetus or Sea Eagles are among the largest and most spectacular of the eagles and, along with the unrelated Osprey, are distinctive as a group by being largely fish eaters, all taking live fish from near the water surface. No other eagles prey on fish in this way, although White-tails also take other prey as well as carrion (see Profile). Thus, breeding Sea Eagles are largely confined to sea coasts, offshore islands, large inland lakes and marshes and rivers for breeding.

Haliaeetus eagles occur on all the continents except South America. White-tailed Sea Eagles occur across northern Eurasia from Norway to eastern Siberia, breeding south into northern China. Isolated populations also occur in Iceland and Greenland and the species has bred in the western Aleutian Islands off Alaska. Birds in western Europe are non-migratory although limited dispersal of juveniles occurs. Birds in Russia east to Kamchatka are mainly migratory with birds wintering south to Japan, China and west to the Gulf States. In North America White-tails are replaced by the closely related Bald Eagle (H. leucocephalus) which breeds across the continent south into north-west Mexico. In eastern Siberia White-tails overlap in distribution with the rare Steller’s Sea Eagle (H. pelagicus), one of the most spectacular and largest of all eagles weighing up to 9 kilos. Steller’s breed in the forests of eastern and coastal Siberia especially Kamchatka. Many birds winter in Hokkaido, Japan. Another two Haliaeetus eagles, White-bellied Sea Eagle (H. leucogaster) and Pallas’s Fish Eagle (H. leucoryphus), occur on the Asian mainland, the former from India to Indonesia and south to Australia. African Fish Eagle (H. vocifor) occurs commonly south of the Sahara to the tip of South Africa. Much rarer is the globally threatened Madagascar Fish Eagle with an estimated population of only 240 birds. Sanford’s Sea Eagle (H. sanfordi) has a very restricted distribution, occurring in the southern Pacific islands east of Papua New Guinea and the Solomon Islands.

Haliaeetus eagles, as top avian predators in marine and freshwater environments, are good indicators on environmental quality and health. Because adult sea eagles feed extensively on fish problems in coastal and freshwater environments are likely to also affect sea eagle populations. Good populations of eagles suggests that all is well with fish populations and therefore presumably smaller fish, copepods, etc further down the food chain. Declines in sea eagle populations may be due to other factors such as habitat destruction or persecution. However, declines due to poor reproduction are likely to indicate problems with fish populations and/or environmental pollutants. Thus, Baltic Sea populations of White-tailed Sea Eagles declined greatly and failed to breed successfully during the era of DDT contamination but recovered slowly once DDT was banned in the 1970s. Likewise Bald Eagles in the US suffered serious declines due to DDT and other organochlorines but have since recovered in most areas. However, even today, southern California populations of Bald Eagles are still negatively affected by environmental contaminants such as PCBs, despite banning or restrictions on their use, due to dumping of DDE and PCBs offshore.