The five species of divers that now inhabit the Northern Hemisphere are among the most primitive of birds, with a fossil record stretching back 65 million years. Survival over such an enormous time scale implies ecological success. Their sleek thick necks, gracefully streamlined bodies, and dagger bills, common to all species, give away their almost totally aquatic nature. Divers are known to dive down to 70 m. Their decreased heart rate and the ability of many of their major organs to function at low oxygen levels make these birds superb divers. These birds are outstanding fishing machines, their lobed feet set far back in the body as a perfect source of power for underwater pursuit. With feet so distant from their center of gravity, divers pay the price for aquatic grace with inelegance on land. They can only walk clumsily and shuffle awkwardly from their shoreline nest to the safety of their true environment (a trait thought to be the origin of their North American name loon, possibly a derivation from the Nordic word "lom" meaning clumsy or lame). There are three major species in the Arctic, although two other recognized species that nest more in the taiga forest, black-throated diver (Gavia arctica) and Pacific loon (G. pacifica), also extend into the Arctic regions.
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