On a cold morning before dawn, Libby Mojica worked by headlamp to wire up explosives in a farm field. If all went well, the explosives would launch three rockets to carry a 60-foot net over a bald eagle.

Biologists Mojica and Bryan Watts are trapping and studying eagles along the James River, which runs beside the field at Weyanoke Point in Virginia's Charles City County.

The research should allow experts to help the majestic birds, perhaps by pointing out territories in need of protection.

But field work can be unpredictable. Six days earlier, Mojica and Watts sat in tentlike blinds for three hours-a test of patience and bladder control-but no eagles visited the deer carcasses set out as bait.

Mojica attached a nine-volt battery that would ignite the rockets.

"All right, we're hot,"' she called out as they retreated to their blinds.

The public loves our nation's symbol.

In a survey for the Virginia Department of Game and Inland Fisheries a few years ago, people placed eagles first-with owls and hawks-among animals they most wanted to watch.

In the 1960s and '70s, there wasn't much to see, as the eagle was driven to the brink of extinction across the continental United States. In 1977, there were 33 pairs of eagles in Virginia. Along the James, the birds had died off completely.

"It's the only major tributary of the Chesapeake Bay where the population went to zero," Watts said.

Watts is director of the Center for Conservation Biology, a research organization that's part of the College of William and Mary and Virginia Commonwealth University.

A big culprit behind the eagle's plight was DDT, a pesticide that got in the fish they ate. DDT made the shells of eagles' eggs so thin they broke in the nest.

But something else was clearly going on in the James. Watts and other experts believe that something was Kepone, a pesticide that a Hopewell, VA,-based company dumped in the river in the 1960s and '70s in an environmental disaster that made national headlines.

Research with quail indicated that Kepone, too, made birds' egg shells thin. That toxic double-dose of DDT and Kepone apparently wiped out the James' eagles. The federal government banned the use of DDT in 1972 and Kepone a few years later, and the birds came flying back.

Along the James, the number grew to 16 pairs in 1987, 49 in 1997 and 128 in 2008. Statewide, the total jumped to 584 pairs in 2008.

Today, a nearly 40-mile stretch of the tidal, freshwater James-from the Dutch Gap area near Chester to eastern Charles City County-harbors one of the country's top concentrations of eagles, herons and other fish-eating birds. The National Audubon Society has designated the region an Important Bird Area, a high compliment among conservationists.

"It's important on a continental scale," Watts said of the stretch.

It's not entirely clear why the birds gather so heavily there. But the stretch is bordered by extensive forests and swamps that they inhabit, and the river offers lots of food such as shad and blue catfish.

Now, another challenge.

People, like eagles, enjoy living by water. Development has destroyed an average of 77 square miles of eagle territory-about the area of the city of Richmond-each of the last 20 years in the Virginia-Maryland Bay region, Watts said.

When eagles don't have enough space, they fight. And scientists are seeing more of that.

At the Norfolk Botanical Garden last year, for example, an intruding female knocked a mother eagle off her nest temporarily, causing the mother's eggs to die.

"There are indications now that we're reaching a saturation" of eagle territories, Watts said.

If eagles face tough times again, scientists like Watts hope to be armed with new information to help them.

Watts peered through a small window in his blind. About 7 a.m., a couple of turkey vultures dropped in to check out the deer meat.

That was a good sign. Eagles are extremely wary, but they sometimes take a vulture's presence as an all-clear signal.

Sure enough, an eagle swooped down to dine. From its mottled brown-and-white feathers, it appeared to be young, about 3. Eagles don't get their classic white head, white tail and brown body until about age 5, when they're old enough to breed.

In a separate blind, Mojica fingered a button that would set off the rockets. When the eagle dipped its head to eat, she pushed.

An ear-ringing blast shot the net over the eagle. Like rockets themselves, Mojica and Watts rushed to uncover the struggling bird.

They used a leather hood to calm it-eagles find darkness soothing-and Watts carried the bird like a baby to his truck.

The scientists weighed and measured the eagle and attached a purple leg band identifying it as C-9. The label was so large that anyone could identify the bird from a distance.

The male eagle weighed nearly 8 pounds, with a wingspan approaching 6 feet. That's typical for a male in this area but much smaller than a female, which can weigh 12 pounds and have a 7-foot span.

From the bird's breast, Mojica took a feather, which will be tested for contaminants like mercury.

Watts plans to trap, band and pluck feathers from about 200 eagles over four or five years. This is the project's first year, and C-9 was the first capture.

Scientists know a lot about the number of eagles in the Bay region, but they don't know a lot about how far they travel, how long they live, when they start breeding and the contaminants they are exposed to.

The trapping of C-9 and others may provide that information some day, as people report the birds and their activities in Virginia and other states.

By the James, Watts heaved C-9 into the air. The wild-eyed pioneer took off on strong wings, shot straight downriver and disappeared behind a stand of cypress trees.