Excerpt from: The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/683 

Arguably North America’s best-studied bird of prey, and certainly one of its most admired, the Osprey is the continent’s only raptor that eats almost exclusively live fish. Despite this restriction, Ospreys have colonized a broad array of habitats. One finds their prominent stick nests from mangrove islets of the Florida Keys to coastal rivers of Labrador, from Alaskan lakes to Montana reservoirs, from New England salt marshes to the saline lagoons of Baja, Mexico, and from Carolina cypress swamps to the foggy redwood coasts of California. All but southernmost populations are migratory, vacating their breeding grounds in late summer for rain-forest rivers and fish-rich seacoasts and lakes of Central and South America, returning north each spring as waters warm and fish become accessible. An Osprey nesting in central Quebec and wintering in southern Brazil might fly more than 200,000 kilometers in migration during its 15-to 20-year lifetime. Clearly this is a mobile, adaptable creature, familiar with vast distances and a shifting complex of weather, prey, and habitat.

Ospreys dive feet first for their prey, accessing only about the top meter of water, so they are restricted to surface-schooling fish and to those in shallows—the latter generally most abundant and available. Thus North America’s Ospreys tend to breed most densely where shallow waters abound: Long Island Sound, Chesapeake Bay, and Florida Bay along the Atlantic coast; Baja Mexico’s Pacific coast; Georgian Bay in the Great Lakes; and several large reservoirs and lakes in western states. In many of these regions, as in others, artificial nest sites have helped breeders enormously in recent decades. Historically Ospreys built their nests atop trees, rocky cliffs and promontories, and—on a few islands free of mammalian predators—even on the ground. While some continue to use such natural sites, many have shifted to artificial sites, an astonishing array of them: channel markers in harbors and along busy waterways; towers for radio, cell-phone, and utility lines; and hundreds of nesting poles erected just for this species. This shift has been dramatic in many regions, with 90–95% of pairs choosing artificial sites; predation, loss of trees, and development of shorelines have been driving forces behind the change.

North American Ospreys gained increased recognition during the 1950s–1970s because populations in several key regions crashed. About 90% of the pairs nesting along the coast between New York City and Boston, for example, disappeared during this period; Chesapeake Bay lost about half its breeders; Great Lakes populations also suffered major declines. Studies showed high levels of contaminants (especially DDT and its derivatives) in eggs, severe eggshell-thinning, and poor hatching success. Mortality of adults may have contributed to the decline. Osprey studies provided key evidence in court to help block continued use of persistent pesticides, and Osprey populations recovered rapidly thereafter. Although small pockets of contamination remain, apparently mostly on wintering grounds, by the year 2000 many U.S. and Canadian populations were approaching historical numbers, boosted by a cleaner environment, by increasingly available artificial nest sites, and by this bird’s ability to tolerate human activity near its nests. Phoenix-like, the Osprey has arisen from the ashes of its own demise, a survivor, even a backyard bird in some areas; little wonder the species has become such a powerful totem for conservationists.