It is a myth, but a persistent one, that the Eurasian mute swan is silent its entire life, only singing a final litany as it is dying. In fact, the so-called mute swan is quite vocal, though not loudly, conversing with its fellow swans with a call that I can roughly describe as a light cough or "bark" followed by a prolonged hiss or "purr." I once watched a wounded swan die, quite quickly, and in that brief interval, there was no sound.

In late medieval England this species was a serious food item, much sought after as banquet fare. All of England's swans belonged to the crown, and a license to keep, raise, hunt and eat them could be sold or doled out as a political or profit-making deal for the monarchy. This claim and the tradition surrounding it has persisted in England for hundreds of years. Today, the queen reserves only the swans resident on the Thames as her own.

The Wall Street Journal reported this summer that Queen Elizabeth II, for the first time in her reign of 57 years, personally participated in the annual Thames River swan census. She accompanied David Barber, the official "swan marker" on a voyage upriver on a mission known as the "swan upping," a swan census on behalf of the monarch that dates to the 12th century.

The term "upping," current since at least 1560, seems to have come from "swan hopping," the act of capturing them. It's said the best way to control these big active birds is to sit on them, They're then tied up, with special swan ties, until a mark is painlessly applied on a juvenile bird's beak. The mark will last the life of the bird.

In the 1980s, Britain's native swan population was falling. This was traced to poisoning from lead fishing sinkers, ingested as the birds sieved river bottom muck for food. The same difficulty among U.S. waterfowl was largely remedied by hunters' switching to steel rather than lead shot. Britain acted to control lead in the environment, and the mute swan population has returned to what is considered normal-about 35,000 birds nationwide. In 2009, the Thames population increased by about 120 cygnets.

In the United States, such an infestation of nonmigratory mute swans-which are not native to North America-would devastate the Chesapeake's submerged aquatic grass meadows. This is largely because the swans feed on the plants during the warm months, when most of the plants' energy is committed to actively growing, spreading to increase acreage, producing seed for the future and storing resources in buried rhizomes or tubers for the next year.

When I came to Maryland to live in 1971, North America's tundra swans-also known as whistling swans-were an annual winter feature on the Patuxent near Benedict. They thronged the winter fields at Charles County's Serenity Farm, and Bob Hall's Calvert County cornfields near Hallowing Point. At Osborn Cove on the Patuxent, a few of these native winter migrants, distinguished by their black bills, would visit us each winter, stately swimmers with their heads held high. Their distinctive trumpet-like cries were thrilling to hear on autumn and winter nights. These were winter birds, though, and left each spring to fly north and breed.

I did not believe mute swans would be a threat to the Bay the first time I saw them in numbers decades ago as I sailed into Tar Bay on Maryland's Eastern Shore. This was around 1984, after tundra swans had long left the Chesapeake. I was stunned to see a big flock of swans feeding on Bay grass beds then just recovering from the nadir of the Chesapeake's submerged aquatic vegetation. Perhaps a hundred of them formed a ragged pattern like white leaves blowing against the distant woodland of the mainland. The musical sound from the wind whistling through the long primary feathers on their wings was astounding as they flew off southward. I was soon to be disabused of my wonder.

Mute swans, brought from overseas, were already established on Long Island Sound and the Hudson Valley in the late 1940s, and were wandering south to the New Jersey coast and northeast to southern Massachusetts by 1951.

The Chesapeake population seems to have wholly descended from a group of mute swans that escaped from captivity during a hurricane in the 1950s. They never looked back toward domesticity and prospered in the wild, with the Bay's vast underwater grass meadows providing what then seemed an inexhaustible food supply. At that time, they were virtually the only large avian grazer present all year and the population began unchecked growth.

Many waterfowl-like swans-are vegetarians. The brant, a goose, was so specialized in its preference for eelgrass that during the 1930s, their numbers were greatly reduced when this plant died off from a pest infestation. Some members of the East Coast brant population "learned" to eat the pollution-tolerant alga, sea lettuce, and have prospered.

When Chesapeake Bay's grasses collapsed under pollution effects and water turbidity stress in the years after 1972's Tropical Storm Agnes, that food resource was no longer inexhaustible. With the disappearance of Bay grasses, many waterfowl populations, already having problems in their Canadian breeding grounds, were hit hard.

Mute swans, having almost the entire Chesapeake grass beds to themselves during the summer growing season, spread out to areas where the grass resources were still available. These were often refuge areas-such as those surrounding the middle Bay islands. By the 1980s, there were thousands of mute swans around the Bay. They had full rein to eat the shoots and reproductive parts of these plants just when these parts were most needed to propagate and help restore grass beds.

Parts of Maryland's Tar Bay are enclosed by low isles and peninsulas of sand and oyster shell, an area collectively called The Marshes. But there is little marsh about them, the largest being capped only by small patches of dune grass.

In June 1990, I sailed with former Chesapeake Bay Program Director Bill Horne to these islands. My log reads: "As we came inshore I was amazed to see at least 500 swans ranged all along the Bay front. Like a huge fleet they steamed into Tar Bay, no doubt decimating the SAV beds...An amazing sight I've never seen on this Bay in June and July. Once ashore on the islands, I found the swans had littered the beach on this one sandbar with feathers along with my estimate of 200 pounds of swan droppings as big as those left by a sizable dog-or human."

Walking along this shoreline was a dance of picking one's way among feces. Rain and tide had leached nutrients from piles, which drooled brown toward the water. Bright green algae, responding to the nutrients, added green streaks where material had been exposed awhile.

"These banks, fortunately, are rarely visited-and should be so in deference to the birds. I made our intrusion as gentle as possible by staying largely below the tide line. As an example of how rare intrusion is, an osprey had her nest on the ground hardly a yard above the water. Two beautiful, healthy chicks glared at me with baleful red eyes...powerful, meat-eating predators in the making.

"South along the curving banks, least terns and black skimmers nest atop the berm in thin vegetation with eggs right on the hot sand, maybe 10 feet apart, one or two in a clutch. This is as far north on the Bay I've seen skimmers. In other years we've seen them at Tangier Island around Cod Harbor.

"The sky was full of terns, hundreds wheeling and skirling against sun and blue sky, and the air rang with their cries. Certainly a premier experience with birds for me. I quickly left them, and in a minute or two they settled back to their business."

The swans, however, used these beaches as a "loafing area" and in a year or so, threatened away or trod upon, the nests of all these birds, which failed to thrive. The skimmers were gone and most-then almost all-of the terns left.

In September 2000, I took my dinghy into Tar Bay, operating on a tip from Bob Orth, a scientist at the Virginia Institute of Marine Science. He told me that aerial surveillance had shown a dense bed of widgeon grass there.

As I approached, its location was visible not by the grasses, but by the mass of swans grazing at its epicenter. A rough count of the flock was 175 birds, but as I approached they divided and raised their long necks, which had been tearing up grass (their heads 2.5 feet underwater) and my recount was 230 birds, plus another 141 at nearby Opossum Island. Each of these big critters will daily consume about 5.5 pounds of grass, (collectively 2,040 pounds a day or approximately 61,215 pounds a month). In the 1980s, when the grass beds in Tar Bay began to recover from their historic lows, the swans came in with increasing numbers, maybe eating 2.5 tons a day and the recovery of this valuable resource failed.

Later that same year, when I returned with a friend, Monaca Noble, we approached a large flock of feeding mute swans-maybe 250 birds-and what I had guessed to be about 200 more at the head of Tar Bay, site of another dense bed at the time. These all flew off with great drama and a remarkable rush of sound. Widgeon grass, the dominant Bay grass at this location, had been pulled up, and we found plant parts and actively sprouting rhizomes washing ashore on Opossum Island.

I witnessed comparable flocks down on Tangier Sound and around Bloodsworth Island. Together, these flocks were likely consuming 74,250 pounds of seeds, vegetative grasses and rhizome a month.

As these beds were grazed down-and subject to other stresses-their productivity faltered, causing groups of swans to move to other locations. Some hung around restaurants, like one popular spot on Broomes Island along the Patuxent. Breeding pairs would bring their six or seven cygnets around, and customers would toss bread to them. People loved them and maybe felt that somehow they were helping the Chesapeake by feeding these beautiful creatures.

At home, on the creek near Osborn Cove there were at first three, then seven, then nine. One spring night when I went down to swim after work-a time when rich SAV beds carpeted the cove's shallows-there were 42 of them waiting for me to leave so they could resume plundering the grasses.

It wasn't long before pairs started trying to nest on the end of our sandbar. Once they began sitting on the eggs the cob, or male, began busking, taking aggressive postures toward me. He rushed me while I was swimming up to my neck one day. The 6-foot wingspan coming at me was terrifying. A man was once drowned in such a situation.

When I'd row past in my dinghy, he would rush the boat, banging into the oars. A neighbor's 10-year old daughter was rushed in her kayak, the swan trying to climb up on the deck until her father drove it off. My friend Frank, who'd been fishing in a small outboard with his dog, said the swan came up on the bow, driving his pet into the water.

Maryland by this time was authorizing people to paint vegetable oil on the eggs, which stopped their development. I waded out the sandbar to do this when the swan came at me 15-20 miles an hour, only to be fended off with a pole at the last moment.

Back on the dock, I found myself shaking and my heart pounding. I was well aware that a smaller person's arm could be broken by the powerful swan's flailing "wrist" bones. Oiling the eggs, a final total of seven, eventually discouraged this pair, but I knew they or others would be back the next year, and the next. I'd had quite enough interactions with mute swans, which are not a natural part of this ecosystem.

Maryland convened a panel of wildlife biologists, waterfowl experts and private interest groups that decided to continue the state's efforts to control the flock. This included egg oiling or addling (shaking) them to scramble their contents. But staffers were unable to find many of the eggs, and the swans hatched and quickly grew, making it necessary to either shoot or capture and dislocate the neck vertebra of birds in a population that had grown unsustainably large.

This was a difficult choice. No one takes pleasure in killing creatures so large and lovely. It was also opposed by people who bought grain by the bucketsful to feed the wild flocks and thus encourage still further reproduction. Despite these tensions, Maryland Department of Natural Resources staff eventually reduced the swan population to 500-600 birds.

In 2008, I was asked by the DNR to serve on another mute swan advisory panel to help re-evaluate this policy. The killing of birds was distasteful to all parties, but if the population was left alone, they would quickly increase toward the thousands that had ranged the upper Bay before. To maintain a "steady state" of 500 already unwelcome birds, a large number would have to be killed, despite egg addling, each year. The majority on this committee agreed that mute swans in the wild should be extirpated from the Maryland portion of the Bay, with dissenters making their own argument for a policy of live and let live.

The panel's report, both pro and con, was brought to Maryland Gov. Martin O'Malley for a decision. As a result, the Maryland DNR will continue to remove swans from the wild. This can only be done in sufficient numbers by killing them. Based on my own experience over more than two decades, I supported this policy, although it was with great sadness.

Removing these nonnative birds will not by itself restore the Bay, but like eliminating invasive snakeheads and the rapa whelk, which preys on oysters, anything that prevents nonnative animals and plants from getting a foothold on the Chesapeake will help.