The North American osprey, Pandion haliaetus carolinensis–whose species name is derived from the Greek ‘hals’ (salt or sea) and ‘aetos,’ or eagle–is the only diurnal bird of prey that feeds exclusively on live fish.

For many years the osprey has been a symbol of the plight of the Chesapeake Bay and of the potential for its recovery. The species is situated at the top of the aquatic food chain, which makes it a good indicator for detecting habitat destruction, dwindling fish populations, and the contamination of the environment.

In the 1960s the number of ospreys in the Bay region decreased dramatically due to the widespread use of pesticides such as DDT, which caused the birds to lay eggs with extremely thin shells that resulted in lower hatch rates. With the U.S. ban on DDT in 1972 and the reversal of the Coast Guard’s policy of dismantling osprey nests on channel markers, osprey numbers began to rebound. Today ospreys are a common sight, and it is estimated that more than 2,000 pairs currently nest in the Bay area.

Physical Characteristics

• The fish-hawk, as the osprey is also known, is a large raptor, with a body length of about two feet, a wingspread of five feet, and long sharp talons. Its back and long arched wings are brown, and white plumage covers its breast and upper legs.
• The characteristic M-shaped crook in its wings, its wrist patches, dark brown stripes across the eyes and the dark bands on the underside of the tail identify an osprey in flight.
• Based on recent DNA testing, ospreys are thought to be more closely related to eagles, hawks and Old World vultures than previously thought.
• Like most female birds of prey, female ospreys generally are larger than males.

Habitat and Life Cycle

In the Chesapeake Bay, unlike other regions, most ospreys do not start breeding until they are five to seven years old. Many of the over-water structures that are necessary to protect them from predators already have ospreys in residence, so new breeders must either displace older, established nesting birds or find another, perhaps marginal site that others have refused for good reason. If there are no suitable nesting sites available, young ospreys may be forced to delay breeding until they find a single bird with an established nest–possibly an older bird whose mate has died.

• North American ospreys are migratory raptors, which overwinter in South America (they are as familiar with tropical rainforests as with northern lakes and estuaries) and return to the same nesting sites on the Chesapeake for their spring courtship.
• Their habitats include shallow water estuaries, lakes, and rivers.
• Ospreys build their conspicuous nests on tall, offshore structures such as channel markers and duck blinds to protect their young (from human activity and predators such as racoons) and to place the birds near their food supply.
• Ospreys usually mate for life. March ushers in a five-month period of partnership to raise their young.
• Females lay three to four eggs by late April, and rely on the size and bulk of their nest–with its pronounced depression at the center–to conserve heat. The eggs are approximately the size of very large chicken eggs, mottled and the color of cinnamon. Osprey eggs incubate for about five weeks.
• After hatching, the 2-ounce chicks become fliers within eight weeks. When food is scarce, the first chicks to hatch are the most likely to survive.
• In spring and summer ospreys find an abundance of medium-sized fish, such as menhaden, to feed their young. Males forage widely, while females stay on or near the nest.
• Ospreys hunt by soaring over water, scanning for surface schooling or spawning fish. They are spectacular divers: once they have sighted their prey, they fold their wings tightly, descend swiftly and enter the water feet-first, often submerging completely. They also perform shallow scoops for fish near the surface.
• In areas of low fish abundance often only one osprey nestling will survive, but in highly productive areas two or three may survive each year.

Twenty to thirty years ago ospreys in the Chesapeake region faced possible extinction, because the species couldn’t produce enough young to maintain the population. Since the ban of DDT in the early 1970s, however, the ospreys, as well as other affected species, are making remarkable recoveries. Other restoration strategies, such as artificial nest construction, also have helped, but land development can still threaten habitat. Active nests used to be removed from channel markers and buoys. However, now you must get a permit to remove them.

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For more information, contact the Chesapeake Bay Program Office:
410 Severn Avenue, Suite 109, Annapolis, MD 21403 / Tel: (800) YOUR-BAY / Fax: (410) 267-5777.

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Last modified: 12/11/03