ASNH Osprey Project: Information about Ospreys

About Ospreys

Ospreys at the nest.

Photo by J. Munier

The Osprey

The osprey is a large fish-eating raptor with a wingspan of more than five feet. It is in a family of its own, separated from other hawks, eagles, and falcons by its unique taxonomic structure and evolutionary adaptations. The osprey is found throughout the world -- in every continent except Antarctica. It is one of the most cosmopolitan raptors in the world; equally at home on remote Scottish lochs, Australian beaches, or New York City parking lot light towers.

The osprey is dark brown on the upper wings and back and white on the belly and chest. The head is well marked with brown feathering with a distinct dark eye stripe.

It has powerful feet and very long, sharp talons. The underside of its feet are equipped with pointed barbs which help hold on to slippery fish. It also has a reversible toe, again to aid with carrying its prey. This toe normally faces forward when the bird is perching (three forward, one back). When the osprey catches a fish, this toe can be reversed to allow two forward and two back, allowing a much better grip on the fish.

When carrying fish long distances, the osprey will turn the fish head-first (torpedo-fashion) to reduce wind drag.

Recovering From Disaster

US populations of ospreys were decimated in the 1950s and 60s due to the widespread use of DDT and other pesticides which contaminated aquatic food chains and caused abnormalities in the eggs of ospreys and other raptors. By 1970, ospreys had been almost eliminated from their former strongholds in the eastern US.

Here in New Hampshire a few pairs hung on inland around the shores of Lake Umbagog and along the Androscoggin River north of the White Mountains. In the 1980s, the Audubon Society of NH working in conjunction with the NH Fish and Game Department began to monitor this small population. These birds seemed to have escaped the ravages of chemical contamination, but were breeding poorly resulting in slow population growth. Biologists began to suspect that mammalian predators -- particularly raccoons -- were robbing the nests of eggs and young. Sheet-metal collars have been placed around the trunks of nesting trees to prevent predators from climbing to the nests with dramatic results; osprey nesting success increased and the population grew. Although the osprey is increasing in NH, it is still listed as a threatened species.

Nesting

Wherever the osprey builds its nest, be it a tree, utility pole, light tower, or channel marker, they always build big -- one of the largest nests built by any bird -- at least three feet deep and five feet across. The main structure of the nest is built of sticks, some as long as five or six feet. The nest is lined with bark, moss, dry grass, seaweed, and clods of earth. Ospreys are not fussy about what they add to their nests. In coastal areas they will pick up all kinds of flotsam and jetsam from the shoreline -- bones, skulls, plastic, paper, even on one occasion a lost toy sailboat!

Food

The male arrives with a fish.

Photo by J. Munier

The osprey is the only diurnal raptor in the world to feed exclusively on live fish. They catch their prey in spectacular fashion, diving feet-first in a plunge-dive from perhaps a hundred feet above the surface of a lake, pond, river, or estuary. Ospreys will take whatever fish is abundant and easy to catch at the time. Fish of less than a pound in weight are usually caught. Here at Lake Massabesic we have seen them bring sunfish, perch, trout, pickerel, and bass to the nest.

Pioneers

Ospreys spend our winter months in Central and South America. They return to NH in April and spend the summer and early fall here; heading south again in September.

Young ospreys spend at least a year and a half in the tropics; usually returning at 2 year-olds. These youngsters (particularly the males) usually return to the area where they were hatched. Although not old enough to breed, they begin to look for suitable nesting sites and may even build trial nests or associate with potential mates. When they return the following year they are sexually mature and ready to breed for the first time.

These first-time breeders may join a mature bird at an established site; perhaps replacing a lost mate, find another young mate and take over a vacant nest, or build a new nest close to an existing active nest, resulting in loose clusters of nests.

Here in NH, in 1999, we had a cluster of 23 occupied nests in the Androscoggin River watershed. Since 1989, a cluster of four nests has grown around Great Bay. Within the last five years a cluster has formed in the Connecticut Lakes and in the upper Merrimack River valley. Perhaps the nest erected in 1997 at Lake Massabesic will form the nucleus of a southern NH cluster.

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