A male and a female osprey whirled in the air above their nest on the Patuxent River, swooping together, then wheeling away. After separate odysseys to Central or South America, the pair had reunited at the nest where they raised their young together last year.
They joined dozens of other osprey pairs that return to the Jug Bay Wetlands Sanctuary in Lothian around St. Patrick's Day each year. The birds busy themselves sprucing up last year's nests and reigniting the spark with their mates, a naturalist at the sanctuary said.
Ospreys were once nearly extinct because of the pesticide DDT, but their numbers have soared in recent years because of environmental safeguards, said Karyn Molines, a naturalist at Jug Bay. The Chesapeake Bay is home to one of the largest osprey populations in the world, and more than two dozen breeding pairs nest at Jug Bay, Molines said.
"People come from Europe, where the ospreys never made a comeback, and they are amazed that we have so many," Molines said.
Visitors to Jug Bay watch the brown-and-white hawklike birds perform elaborate mating rituals such as the "fish flight," in which the male zips around his mate waving a large fish. During breeding season, the male might present as many as eight fish to the female each day.
Mating - which lasts for seconds - is repeated many times in the ensuing weeks, not just for procreation but also for pair-bonding, Molines said.
In mid-April, female ospreys lay the first of two or three speckled brown eggs the size of a jumbo chicken egg. The female rarely leaves the nest during that time and relies on the male to bring her fish.
The eggs hatch at different times, ensuring that the first chick will be well fed but leaving less food for subsequent chicks. Because ospreys consume nothing but fish, and young ospreys eat up to 6 pounds of fish each day, the third chick survives in years when fish are plentiful.
Ospreys have a distinctive fishing technique. Unlike kingfishers or pelicans, which plunge headfirst into the water for fish, ospreys snag fish with their four opposable talons. Short spikes on their feet pierce the fish's flesh and allow the birds to grip the fish more tightly, Molines said.
In June, osprey chicks make their first flights. "They rise straight up into the air," Molines said.
Unlike most birds, ospreys are able to fly straight up or down, which inspired Boeing Aircraft Co. to name a vertical-takeoff aircraft after the osprey. On longer flights, ospreys fly with crooked wings, like seagulls.
The ospreys nest at the sanctuary until August, when the adult ospreys head south for the winter. "The young stick around for a while, like, `Hey, who's going to feed me?'" Molines said.
Young ospreys leave a few weeks later and stay in Central or South America until they reach breeding age, two years for a male and five years for a female. Then they return to the area where they were born to find a mate and build a nest, which young ospreys often botch the first time, Molines said.
Ospreys build their nests on raised flat areas in or near the water, such as high tree stumps or hunting blinds, to protect chicks from snakes and raccoons, Molines said.
As the summer sun intensifies, the parents build the nest walls higher to protect the chicks from the heat. Mother ospreys plunge into the water and sprinkle water on the young to cool them, Molines said.
In the 1960s, ospreys were nearly wiped out by DDT that washed into the bay from farms along the watershed, Molines said.
As the pesticide traveled up the food chain from small fish to larger fish to osprey and other predators, it became more destructive. DDT caused ospreys to lay eggs with brittle shells that frequently broke and rarely hatched. When Maryland banned DDT use in 1972, two breeding pairs lived on the Patuxent, Molines said.
The number of ospreys in Maryland has returned to 1950s levels, said Chandler Robbins, an ornithologist with the Patuxent Wildlife Research Center. More than 2,000 pairs of ospreys nest in the bay, according to the Maryland Department of Natural Resources Web site.
"It's an ecological success story," Molines said.
Don Merritt, a biologist with the Horn Point laboratory in Cambridge, cautioned that ospreys could be threatened by pollution and declining numbers of small fish such as menhaden. Ospreys feed on larger fish, such as striped bass, that depend on menhaden for food.
Access to the 1,400 acres at Jug Bay is strictly regulated. To preserve the habitats at Jug Bay, visitors are allowed only on Wednesdays, Saturdays and Sundays, and only with reservations.
Several other parks, refuges and sanctuaries line the Patuxent River, which divides Anne Arundel and Prince George's counties.
The sanctuary staff plan events to teach school groups and families about the diverse plants and animals, including 270 species of birds, that live at Jug Bay.
The mud at the refuge is pitted with the spindly hand-shaped tracks of raccoons and the deeper paw prints of otters. Swirls left by muskrat tails wind around the heart-shaped shoots of the spatterdock plant. In July, the river will be thick with 3-foot-tall spatterdock, Molines said.
Fences in the water protect wild rice, an endangered native plant, from young Canada geese, Molines said as a flock of gulls scattered at the sight of a bald eagle.
While the female osprey munched on a threadfin shad, Molines pointed out signs of early spring, such as sprigs of yellow flowers blazing from the spicebush, a nuthatch fluttering through the red-tipped branches of a maple, and male redwing blackbirds defending their territory studded with dried cattails.
"It's invigorating," Molines said of early spring at Jug Bay.