It's a chilly November afternoon on the Choptank River on Maryland's Eastern Shore. As watermen in workboats motor back to harbor for the evening, the moon rises and airplanes trace silver trails across a darkening sky. A strange, unearthly laughter wobbles across the undulating waves. It's the call of a loon—a fishing bird sometimes called the "spirit of the north." Loons spend most of the year in Canada and the Northern United States. But every fall, loons visit the Chesapeake Bay during their long migration to warmer waters off Florida and the Carolinas.
Dr. Paul Spitzer, a biologist who studies loons, is out in a motorboat counting the birds, as he does most autumns, when the trees lining the shores turn gold and crimson. He spots a chorus of the birds spread out to surround a school of small fish called menhaden.
"When these birds are in a long arc this is, it is like a living fishnet," Dr. Spitzer said, watching with binoculars as the loons feast on their banquet, then spread their wings to preen and oil their feathers. "The presence of loons here on the Chesapeake Bay is very much one of the signs of the season."
The birds look, well... a bit loony—with thick, torpedo-shaped bodies, black heads, and large webbed feet that make them walk awkwardly. But they are lords of the water, powerful swimmers capable of diving 150 feet down and remaining underwater for long periods of time. Loons have oil-slicked feathers and solid, heavy bones to help them dive. Their eyes are blood-red, evolved to help them see underwater.
The relatively meager size of the flock on the Choptank is emblematic of a broader change Dr. Spitzer said he has witnessed over the last quarter century, as fewer and fewer loons appear to be visiting the Chesapeake Bay.
"Our count on this flock is about 85, our total count on the day is about 120," Dr. Spitzer said. "That would perhaps be 20 percent what a survey here would have found 25 years ago. We would typically have found 500 or 600 birds."
Why the decline?
"Well, the argument is that the food for loons just isn't here," Dr. Spitzer said. "What we are seeing is the number of birds supported by the food that's here."
Dr. Spitzer and other scientists are concerned that the loon's main prey here in the Chesapeake—small, oily fish called menhaden—are in decline.
A study released last year by the Atlantic States Marine Fisheries Commission (ASMFC) concluded that menhaden have been overfished in 32 out of the last 54 years, including in 2008. The population of the fish is at the lowest level on record.
Industrial fishing fleets out of Reedville, Virginia, caught an estimated 183,000 metric tons of menhaden last year, which were ground up to manufacture fish oil pills, livestock feed, and other commercial products.
On November 9, 2011, ASMFC voted to impose new fishing guidelines that could eventually reduce the catch of menhaden. But the Virginia General Assembly must still vote on any catch restrictions, which could spark a battle.
Hanging in the balance of the fight over menhaden is the fate of a wide variety of species in the Chesapeake Bay that eat menhaden, including loons and striped bass.
Loons, bass, and menhaden are all tied tightly together in the Bay's web of life. A recovery of striped bass populations two decades ago, driven by tight restrictions on catching the fish, coincided with a decline in both menhaden and visiting loons. This has led Dr. Spitzer to speculate that there could be a connection, with stripers eating fish that loons also need.
During his trip out to the Choptank River, as the flock of loons dove for fish and hooted to each other, Dr. Spitzer and the captain of the boat grabbed their fishing rods. They quickly reeled in several striped bass, which flipped and slapped their tails. Back on shore, the captain, Jim Price, sliced open the stripers' stomachs to reveal that almost all of them were full of menhaden.
Menhaden are a keystone species in the Bay. And the decline of menhaden could be throwing the Chesapeake's whole chain of life out of balance, said Dr. Bryan Watts, Director of the Center for Conservation Biology at William and Mary and Virginia Commonwealth University.
He said the Chesapeake Bay is famous as a stopover for a spectacular array of migrating birds, from loons to osprey and pelicans. But he warned this part of the Bay's identity could slip away if there are no fish for the birds to eat.
"As the fish go," Dr. Watts said, "so do all the species that depend on them."
If the call of the loon vanishes from the Chesapeake Bay, autumn will not be the same here. A spirit of the season will be lost.