A spring drama is unfolding on the Potomac River.

Ospreys (Pandio haliaetus) have returned from their southern wintering grounds and are mating, building nests and incubating eggs. Ospreys are raptors, around 23 inches in length with a four- to six-foot wingspan, birds that soar and hunt over water. They are chestnut brown and white, with a prominent, dark eye stripe on the side of their white head. Ospreys are often confused with bald eagles.

Also called the “fish hawk,” they scan the water, hover and suddenly plunge feet-first onto their unsuspecting piscine prey. Expert anglers, their catch rate success may be as high as 70 percent, say experts at Cornell University’s Lab of Ornithology. After clutching a fish in their talons, ospreys usually fly to a nearby tree limb to eviscerate it or take it back to the nest to its mate or young. One telling behavior of ospreys is that they always carry the fish “aerodynamically correct” with the fish’s head forward to reduce wind resistance. 

Osprey pairs build bulky nests near water in trees, on platforms, utility poles, channel markers, waterfowl blinds and other structures. Last year, a sailboat at Belle Haven Marina was stymied for the season because ospreys chose it for a nest site.

An osprey nest is an unkempt jumble of sticks lined with materials like grasses and flotsam with streams of plastic and other debris at times protruding. Oddities like shoes, cans and even a Barbie doll have been found in their nests. Many osprey pairs return to the same nest each year and “spruce it up” with new material.  After adding materials year after year, a nest can be ten to 13 feet deep and three to six feet across. 

No one has determined how many osprey nests are on the Potomac this year, but there are four known nests in the Dyke Marsh Wildlife Preserve, probably more. One accommodating, people-tolerant pair has nested 100 feet from the Belle Haven Marina boat ramp since 2006, says Larry Cartwright, a Friends of Dyke Marsh member who leads breeding bird surveys.

On Saturday, Yukun Xing watched the pair for an hour. ”Raptors are cool,” he said. “They look sharp.” Xing took pictures of the ospreys.

Last year, there were ten nests in Dyke Marsh and young survived in five. Like bald eagles, osprey numbers were reduced by eggshell thinning caused by the pesticide DDT from the 1950s to 1970s. Once DDT was banned in 1972, eagle and osprey numbers began to rebound, what many call “a conservation success story.”

Ospreys will incubate two to four eggs in April and raise their nestlings in May. The young will fledge soon after Independence Day. Adult ospreys will return next year in early March from their southern wintering grounds—Florida, the Caribbean, Central America and South America and one of nature’s amazing rituals will repeat. 

Become an Osprey Watcher

“Osprey Watch” at William and Mary’s Center for Conservation Biology is recruiting “citizen scientists” to collect information on breeding ospreys. The project hopes to address three of the most pressing issues facing aquatic ecosystems—global climate change, depletion of fish stocks and environmental contaminants.

“Ospreys are one of very few truly global sentinels for aquatic health. ...Nearly all populations breed in the northern latitudes and winter in the southern latitudes, effectively linking the aquatic health of the hemisphere,” says the web site. 

You can watch the activity in an osprey nest at Gloucester Point, Va., via a live camera