The Osprey

(Pandion haliaetus)

by Jay Sharp

The Osprey. Photo by Mike Baird from Morro Bay, USA.
Osprey. Photo by Mike Baird from Morro Bay, USA.
("Marc Schulman of Orchid Outriggers, Los Osos, CA, took me out in his 17' outrigger canoe to photograph these Ospreys, Egrets, and Surf Scoters. We paddled six hours.")
Photo Courtesy Wikimedia Commons. 27 September 2006.

The osprey, one of the most widely distributed raptors in the world, holds residence on every continent except Antarctica, taking live fish – 99 percent of its diet – from seashores, estuaries, rivers and lakes. Often migrating long distances in spring and fall, the bird – elegant on the wing – may fly well over 100,000 miles during its lifetime. "Clearly," said Alan F. Poole, Rob O. Bierregaard and Mark S. Martell in their article "Osprey," the bird "is a mobile, adaptable creature, familiar with vast distances and a shifting complex of weather, prey, and habitat."

Distinctive Features

Mature male and female ospreys have similar plumage, often making it difficult to distinguish between the sexes.

  • Size: Generally larger than hawks but smaller than eagles, the adult osprey measures approximately two feet in length, and its wings span some five to six feet. Typically, the bird weighs three to four pounds. Usually, the female is somewhat larger than the male.
  • Adult plumage: As the Audubon Society's Master Guide to Birding says, the osprey "is brown to brownish-black above and white below..." It has "buff to brown speckling on the breast." The bird's "head is white with a dark crown and a wide, dark brown eye stripe." Plumage is dense and oily, minimizing soaking after predatory plunges into the water.
  • Wings: In flight, each wing "wrist" (carpus) bears a dark feather patch and crooks slightly inward, serving as a distinctive species indicator when the bird is in flight.
  • Feet: On its grayish-colored scaly feet, the bird has spiny pads and four strongly hooked black talons (including a reversible outer one that can turn backward or forward). This anatomical arrangement facilitates clenching and securing a slippery wriggling fish. In flight with a catch, the osprey positions the prey face forward to minimize air resistance.
  • Vision: Like other raptors, the osprey has excellent eyesight, several times more acute, in fact, than that of a human. Moreover, the osprey's eyes face forward, which provides excellent depth perception. Its eyes are key to finding prey fish in the water.
  • Vocalizations: The osprey is quite vocal, says David Allen Sibley, The Sibley Guide to Birds. Repeatedly, it issues "short shrill whistles tewp, tewp, teelee, teelee, tewp..."
  • Locomotion: Although ungainly on the ground, the osprey flies with grace and with speed—25 to 30 miles per hour.

Distribution and Migration

The osprey breeds and winters in six of the earth's seven continents. In North America, it breeds from Alaska across Canada to Newfoundland then southward into the United States' western and northeastern states. Many migrant populations winter in U. S. and Mexican Gulf states, southern California, several Caribbean islands, Mexico's Gulf of California and Pacific states and Central America's Caribbean and Pacific coastal regions. Year-round residents spend the year in U. S. states in the southeast and some locations in the southwest as well as in Mexico's Gulf of California states and a few other locations. The bird may turn up in unexpected places. For instance, in a drive across western Texas several years ago, my wife, Martha, and I saw, to our surprise, an osprey atop a power pole near the Rio Grande and the Amistad International Reservoir.

The bird's migration range, tracked over long distances by satellite telemetry, has become better understood in recent years. For example, an osprey "nesting in central Quebec and wintering in southern Brazil," said Poole and his associates, "might fly more than 200,000 kilometers [125,000 miles] in migration" during its lifetime.

Habitat and Diet

In both the breeding and the wintering seasons, the osprey frequents areas near the shallow waters of saltwater shorelines, lagoons and marshlands and freshwater wetlands, rivers, ponds and lakes. Historically, said Poole and associates, the bird has built its nest of sticks in the tops of trees or high in rocky cliffs, preferably near the water. In an area free of predators, it might even build a nest on the ground. In recent times, "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."

The osprey feeds almost exclusively on schooling fish, encompassing a wide diversity of species, near the water's surface, but it may on occasion, according to some reports, take species such as a small reptile, a salamander, a small bird or even a small mammal.

Behavior and Life Cycle

Except during breeding season, the osprey lives a largely solitary life. When foraging, typically around dawn or dusk, it may hunt from a perch or from flights or in glides above the water's surface. Sighting fish schooling, it may hover briefly above the surface then plunge in feet first, said Poole and his associates, following a long, shallow approach for fast swimming fish at the surface or a steep approach for slower fish just below the surface. It may capture a fish that weighs half as much as the bird itself, so it must exert powerful wing strokes to lift itself and its prey from the water. It succeeds in capturing prey in more than half its plunges.

When not foraging, the osprey spends its daylight hours preening, resting and feeding and its nighttime hours resting. It is an "Active preener and bather," said Poole et al. It bathes at the edges of salt and fresh water shallows, ducking its head and beating its wings. Fastidious, the bird flicks fish scales from its bill, often wiping it on a branch, and it cleans fish remnants from its feet, often washing them in shallow water.

During the breeding season, which begins soon after the spring migration northward, the male performs a sky-dance display to court his mate, usually above a site that he has selected and perhaps begun nest construction. To impress his mate, he passes high over the site in a slow, undulating flight, possibly grasping a fish or nesting materials in his talons. He may hover briefly, flapping his wings vigorously and displaying his present. Throughout, he issues a screaming call of romance. If the female signals her approval by soliciting food, he feeds her, and the two copulate repeatedly, consummating a long-term breeding season bond.

The two then complete their nest or refurbish their previous season's nest, with the male fetching materials for construction and the female arranging them to suit her taste. She will continue to enhance the nest throughout the nesting period. Typically, their nest, well-lined and substantial, will measure two- to three feet in diameter and a several inches in depth, although it may reach substantially larger dimensions through time.

Soon after the nest is ready, the female lays the first of two to four two-inch-long, creamy white- to cinnamon-colored smooth speckled eggs—one every two to four days. For the next five to six weeks, the male takes primary responsibility for feeding the female, and the female, for incubating the eggs. This will likely be their only brood for the season.

After about five weeks, the young, softly peeping and covered with down, begin to hatch, in the order in which the eggs were laid. In the coming weeks, the male forages and brings food to the nest. The female distributes the food to the chicks, offering them only small pieces in their downy days and much larger pieces in their fledging days. Older chicks may bully their younger and smaller siblings for food. The male and female may guard their nest from intruders and predators by shaking their wings and fanning their tails. They may scream loudly. They may chase an intruder if it approaches too closely.

After some seven to eight weeks, the chicks have fledged and tried their wings. Finally, they take flight. Although still fed by its parents, especially the male, during the first several weeks out of the nest, a young osprey soon begins to learn the business of foraging and preparing for its first migration. It will reach sexual maturity at three to four years old. If it survives to maturity, it may live for 20 to 30 years or more.

Life's Hazards

In the mid-20th century, the osprey population worldwide had fallen perilously low as a result of factors such as habitat destruction, hunting and, especially, the insecticide DDT use, but it has recovered in recent years with the construction of new reservoirs, erection of artificial nesting structures and a ban on DDT. The International Union for Conservation of Nature and Natural Resources now rates the osprey as a species of "Least Concern."

Interesting Facts

  • The plumage of the osprey is surprisingly consistent across its worldwide range, according to Poole. This contrasts greatly, for instance, with a more sedentary eagle species that occupies much the same range as the osprey.
  • Eagles sometimes pirate ospreys for food, said National Geographic. "Eagles often force osprey to drop fish that they have caught and steal them in midair."
  • Unlike a bald eagle, which plucks fish from the surface of water, an osprey may become completely submerged in its plunge into the water for prey. It has nasal valves that prevent water from entering its nostrils.
  • During the migration seasons, some ospreys cover distances exceeding 200 miles per day and fly at heights approaching 5000 feet in elevation.
  • Pandion, the first name in the osprey's scientific label, refers to a mythical Greek king whose daughters were turned into fish. Haliaetus, the second name, refers to the Greek words halos, a reference to the sea, and aetos, a reference to an eagle.

 


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