The Osprey, the only species in the family Pandionidae, is one of the world's most easily recognized birds of prey. The mostly white crown set off by a dark stripe through the eye is unique among North American raptors. The rest of the upperparts are dark, contrasting boldly with the white underparts. The breast, especially in females, has a variable amount of dark streaking. From below, the flight feathers of the wing and tail appear finely barred, and a blackish patch shows near the wrist joint. The juvenile birds (less than one year old) resemble the adults but have the dark feathers of the upperparts narrowly edged with whitish and buff. In flight, the Osprey has a unique shape: it flies with the wings slightly arched and slightly bent at the wrist.
Size: Length 43-56 cm (17-22 inches), wingspread about 167 cm (56 inches), weight 1.1-2.0 kg (2.4-4.4 pounds). Though there is overlap between the sexes, females average larger, about 10% more in linear measurements and about 200 grams more in weight.
Voice: A series of 7 to 20 shrill ascending whistles, "kyew, kyew, kyew...."
Range and Habitat
Range: The Osprey is one of the world's most widespread birds, occurring on all continents except Antarctica and many islands. Originally, it nested widely across North America, but contamination with the pesticide DDT led to population decrease and range retraction, including disappearance as a breeding species from southern California. Since the ban on the use of DDT within the United States, the Osprey's numbers have rebounded. In 1997 Ospreys nested in San Diego County for the first time since 1912. By 2000 two pairs were nesting successfully in the county, one at North Island Naval Air Station, the other at Scripps Ranch High School.
Habitat: Because it is specialized for a diet of fish, the Osprey is found normally near water, either fresh or salt. For nesting, it needs a site secure from terrestrial predators, typically a treetop, or now often a man-made structure. Predator-free islands in lagoons also serve, as in San Ignacio Lagoon on the west coast of Baja California. Here the Ospreys build their nests directly on the ground.
Behavior: The Osprey hunts by soaring over the water, then plunging in feet-first when it spots a fish. Not only the claws but the soles of Osprey feet are specialized for holding fish--the soles are studded with rough, pointed scales. When the Osprey emerges from the water with its catch, it orients the head of the fish forward to reduce drag as it carries the fish to its nest or feeding perch. The Bald Eagle's habit of pirating fish from Ospreys has been well known for over 200 years.
Reproduction: Each pair of Ospreys builds a large stick nest and may reuse it for many years. The birds bring new material each year, so old nests may weigh hundreds of pounds. Some pairs have alternative nests among which they shift back and forth from year to year. The clutch consists usually of three eggs, creamy white, and variably but heavily blotched dark. The incubation period is about 38 days, the nestling period 44 to 59 days. Usually only one or two of the young fledge successfully.
Diet: Live fish almost exclusively. The species taken vary greatly by location but typically are 10 to 40 cm long and weigh under 1 kg. Instances are known of Ospreys diving on fish too large for them, getting their talons stuck in the fish's flesh, and being dragged under the water and drowned. Rarely do Ospreys scavenge dead fish or take other animals, possibly only when live fish are unavailable, when they are migrating through unfamiliar territory, or when alternative prey are exceptionally abundant or vulnerable.
Text by Phil Unitt
Photograph © Bob Cranston
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