OSPREY
Pandion haliaetus

      The high-diving osprey is in a class - or in a family - by itself. Technically it is considered a hawk, and it is sometimes called the fish hawk. However, it has evolved so many unique adaptations for catching fish that it differs radically from other hawks. These adaptations are numerous and specialized enough to indicate that the osprey has been evolving separately for a considerable length of time. As a consequence, while other hawks are lumped with eagles, kites and harriers into one family, the Accipitridae, which worldwide contains well over 200 species, the osprey is placed in its own family, the Pandionidae, which contains just this one species. Among these specialized adaptations are the osprey's unique closable nostrils, very useful to a bird that actually submerges while fishing. Its toes are equal in length, not unequal like the toes of other raptors. The outer toe of each foot is reversible (a trait shared by owls), so fish can be grasped firmly with two toes in front and two in back. The underside of the osprey's feet is covered with spiny bumps called spicules that help hold slippery prey. This is our only diurnal (active by day) raptor to have talons that are rounded in cross section. This characteristic, combined with the talons' deeply curved shape, also helps the osprey grip securely.

      The osprey flies differently from other raptors. Despite its large size, it is quite capable of hovering (flying in place), and will frequently do so when scanning the water for fish. In flight the bird shows a characteristic bend or crook in its narrow wings, quite unlike the flat "barn door" shape exhibited by eagles. This long and pointed wing shape gives the osprey the ability to lift up and carry sizable loads. While this bird is almost eagle-sized in length and wingspan, it is lightly built, quite lacking in the bulk that distinguishes eagles. Length averages 23 inches, while wingspan ranges from 59 inches across for the smaller males up to 67 inches across for the larger females. Weight ranges from 2.2 pounds (males) up to 3.9 pounds (females).

      In addition to the gull-like angle in its wings, another osprey field mark (a characteristic used to identify an animal in the wild) is the carpal patch, a contrasting black area on the underside of each white wing, just below the bend. A dark line extends through the eye, and may protect the bird from blinding glare, just as eyeblack gives baseball and football players sun protection. Female ospreys wear a "necklace" of short streaks on the upper chest; in males this streaking is much smaller or absent altogether. In both male and female the upperparts are dark brown, the underparts white. The juvenile or immature (young) birds are similar in coloration, but have white edges to the brown upperpart feathers that make the feathers look a bit like overlapping scales.

      Like the peregrine falcon, another specialized and very successful hunter, the osprey enjoys an extensive geographic distribution. This is, in fact, the most widely distributed raptor in the world. It is found on every continent except Antarctica. In the New World it breeds from northeastern Alaska down to Baja California in the West, and from Quebec to southern Florida in the East.

      The North American osprey population is migratory. Some birds put down on islands in the Caribbean, while others travel as far as Central or South America. A few remain behind along the Gulf Coast or in southern California. Unlike raptors like the broad-winged and sharp-shinned hawks, ospreys do not migrate in large groups. They move southward alone or in pairs, usually following waterways. Older birds will cross large bodies of water like the Great Lakes, while the inexperienced younger birds seem to be intimidated by such barriers. Reverse migration begins on the wintering grounds in March, but the immature birds don't participate in this return trip, remaining behind for another year. While a few ospreys are known to have survived as long as 25 years, average life expectancy is brief, 1.8 years for the species as a whole. In part this is a reflection of the dangers of the bird's first year, when many ospreys die. This high mortality rate among immature ospreys is a cause for concern, since the birds don't breed until at least their third year. In areas where nesting is limited, they may not breed until their fifth year.

      The osprey is our only raptor to habitually plunge feetfirst into water after fish. By contrast the bald eagle, another fish-eating specialist, snatches fish from just under the surface of the water, only rarely submerging. The bald eagle will also feed on dead fish, something the more fastidious osprey shuns. Although ospreys have been observed taking non-fishy prey - from frogs and turtles to small mammals (usually rodents) and birds - their food is almost exclusively fresh fish. Favored species are fairly large, relatively slow fish such as carp, menhaden, mullet and shad that swim or forage near the surface. A hunting osprey typically flies 30 to 100 feet above the water, often in circles or in figure eights. When the keen-sighted raptor spots a likely fish it evaluates the situation, figuring out its angle of attack while it hovers, fanning its wings and letting its legs dangle. Then the bird drops. The angle of the dive varies from 45º to a steep, almost vertical stoop. The osprey often disappears completely beneath the water with a dramatic splash. Seconds later it reappears, shaking water from its dense plumage like a dog. If the dive has been successful (the success rate varies from 25% to 90%), the bird emerges clutching a fish. This is carried headfirst, the better to streamline it, with both feet holding on, one in front of the other. The prize is carried to a feeding perch if the osprey is not hunting for its family. After a short pause to make sure that all movement has ceased, the bird tucks into its meal, beginning with the head. Ospreys cannot carry off very large fish, and heavy prey will be rejected.

      The osprey is never found far from a seacoast, river or lake. To attract ospreys, a body of water must contain a good supply of prey fish, and must be ice-free during the breeding season. The water must be reasonably clear, so the raptor can spot its prey. A breeding prerequisite is a tall structure near the water, on which the osprey constructs a stick-and-flotsam-and-jetsam nest. Tall trees (preferably dead ones, or at least ones with broken tops) are used, as well as crags, and even columnar cacti in desert areas that lack trees. Man-made structures such as utility poles, channel markers and metal pylons are readily accepted, as are custom-designed wheels and platforms mounted on poles. In fact, osprey pairs utilizing artificial nesting platforms raise more young than parent birds that choose natural but unstable sites. Osprey will nest near human habitation far more readily than eagles, although they will object with a high-pitched chereeek if people get too close.

      Ospreys occasionally nest in dense aggregations where food is plentiful. Each nesting pair will drive other ospreys from the area directly around the nest, but apparently a hunting territory is not defended. This colonylike grouping of nesting osprey can be seen in Florida Bay or in Chesapeake Bay, where the nests may be no more than 60 or 70 yards apart. By contrast, nest density in Quebec, where the food supply is much more limited, may be only one breeding pair per 125 square miles.

      Ospreys are usually monogamous (having only one mate), and one pair stays together at least for the breeding season. The birds' real allegiance, however, is to the nest site, which is used year after year. The males return to the nest from winter migration first, followed a few days later by the females. The males reestablish the pair bond by displaying to the females, sky-dancing high above the nest while carrying a fish or nesting material. At times during this dramatic courtship dance the frenziedly-calling male may actually be flying backward! New nesting material is added to the old structure by both sexes. Dead branches are snapped off trees while the birds are in flight, then ferried back to the nest as though they were fish.

      Nesting in North America gets underway from late April to early June. Newly mature breeders usually lay 2 eggs; older birds typically lay 3, or occasionally as many as 5. Incubation can last anywhere from 34 to 40 days. In direct contrast to old reports, modern research has shown that males do help the female incubate. However, the male's main function is to provide food for the nest-bound female, and then for the entire family once the eggs have hatched. The young remain dependent upon the parent birds until just before the fall migration begins.

      Osprey numbers suffered a catastrophic drop after World War II. All along the Atlantic Coast once-active nests were silent and empty. The stretch of New England coastline that extends from eastern Long Island to Nantucket had always supported a healthy number of nests - up to one thousand of them - until the 1940s. By 1970 there were only 90 active nests. Massachusetts, which at one time had as many as 50 nesting pairs, was down to 10. Connecticut too was down to 10 active nests by 1973. Other raptors like the peregrine falcon and the bald eagle were disappearing as well, and by the late 1960s scientists were beginning to realize that a major cause was DDT, which played havoc with the birds' reproductive cycle. The use of this pesticide was banned in the U.S. in 1972. It is a grim irony, however, that the U.S. continues to export DDT to Central and South America, where well over half of the total North American osprey population winters. Other problems, such as habitat loss or degradation, chemical pollution of the water, overfishing and illegal shooting, also take a toll. Widespread conservation efforts are definitely paying off, however. A big factor in the osprey's return is man-made nesting platforms. Ospreys can't nest where there are no suitable nest structures, and shoreline development in New England has removed many of the dead trees the birds formerly used. Fortunately this species willingly uses artificial structures. Dozens have been built and placed in Connecticut and Massachusetts by private individuals as well as by state organizations, and most are now in use. Ospreys are even appearing in places where they haven't been seen for decades. In the spring of 2001, West Springfield recorded the first osprey nest in Western Massachusetts in many years. Once again admirers of the osprey can observe the bent-wing silhouette of this unique bird above our waterways.


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