A pair of mute swans swam in slow circles in the stinking water of the Chicago River near the Diversey bridge. It was an incongruous scene–the majestic birds floating like huge white flowers in the gritty divide between a bowling alley and a public-housing project.

These winter visitors to Chicago aren’t really mute. They just don’t have much to say until after their eggs are laid. That rarely happens in the city, as most of them mate and breed far north of here. When they do speak they hiss and bark as a warning.

Like all swans, mutes are aggressive mainly toward other swans. They don’t bite but can use their wings as clubs. “Children and dogs coming near the nest are often badly beaten or dragged into the water and drowned,” says a 1960 Cook County Forest Preserve bulletin. “A blow from [a male’s] powerful wing has been known to break a man’s leg.”

The pair near the Diversey bridge, which I first spotted in January, were probably the only mute swans on the river this winter, says Doug Stotz, an ornithologist and conservation ecologist at the Field Museum. “Swans are territorial in the breeding season, not in the winter, when you can get big flocks together,” he says. “My guess is that the one pair at Diversey is a reflection of the fact that it is a narrow river and not stupendous swan habitat rather than territoriality.”

The river flows all winter, giving the swans the open water they need. It also has vegetation these herbivores can eat. Stinky as the river is, Stotz says, the weeds in it accumulate relatively low amounts of pollution. If the swans chose to stay beyond March, the riverbanks would offer places where they could nest.

“Mute swans are not very common around Lincoln Park,” devoted birder Kanae Hirabayashi wrote in an E-mail to me. “We see them every migration…out on the lake in March and April and fall (October).” Any pictures of Chicago’s swans on the Web were likely taken by her and are signed with her initials.

“Some winters we see a pair or a pair with their young stay around the Belmont and Montrose harbors,” Hirabayashi went on. “This winter, January 27, I saw two adult mute swans in the Belmont Harbor, and they are still there as of this morning. They sleep and rest on ice.” Attached were three pictures taken that morning.

Hirabayashi, who walks around the harbors nearly every morning, spotted a second pair of adult mute swans in Montrose Harbor. She thought the pair at the Diversey bridge had been commuting between the river and Montrose. “Once I saw all four of them around Belmont Harbor,” she wrote. “One pair was just about outside of the mouth of the harbor, and the other pair was much inside. Seems to me they don’t want to be mixed together.”

Fewer than 1,000 mute swans spend the winter in Illinois, yet this year Wolf Lake on the Indiana border has been home to as many as 100 mute swans as well as one trumpeter swan. Mutes and trumpeters migrate south from around the upper ends of Lakes Superior, Michigan, and Huron in the fall, and Chicago is generally their southern terminus. The larger tundra, or whistling, swans nest in the arctic in the summer and fly south through Chicago on their way to the east coast.

Beautiful as they are, swans are cursed in the northeast. More than 9,500 mutes winter in Pennsylvania, and according to a report by Pennsylvania State University’s extension service, these itinerants are solitary and aggressive, greedily consuming aquatic vegetation that fish and other wildlife need. And their droppings litter green spaces and “can limit recreational use of the area.” The report details lethal and nonlethal ways to get rid of swans.

Chicago doesn’t have a big problem with swans, though we do have lots of Canada geese that make it risky to walk barefoot in many places around the city, including near Diversey Harbor. And ponds in suburban corporate parks are famous for battles between picnickers and gaggles of geese.

Swans aren’t native to the United States but were imported from Europe in the 1800s. Chicago probably got its first in 1868, when New York’s Central Park Zoo gave a pair to the Lincoln Park Zoo. Their ranks grew as captive swans escaped and thrived in the upper midwest’s marshlands.

Illinois quickly became a big nesting ground for trumpeters, but by the 1920s they’d almost died out in the midwest. The 1960 Cook County Forest Preserve report says the birds were “slaughtered for down and breast feathers, as well as for sport.” Mutes were killed too, but the species never became endangered here. An adult male mute swan can have 25,000 feathers and weigh 24 to 50 pounds.

Hormonal changes prompt the swans to start migrating north in mid-March. Mutes and trumpeters both travel in small flocks, apparently tolerating each other during stops. Four or five pairs of mute swans may well stay behind, building nests along the Des Plaines River near Joliet or in the forest preserves. This month the females will lay six to eight eggs.

Most cygnets don’t make it past their first year. “It’s tough being a young bird,” says Stotz. “In most species the vast majority of young do not survive to age one. Predation of flightless young–so less than about four months old–and then starvation or disease in older young are probably the major causes of deaths.” If a mute swan survives its first year it lives an average of six years, though about a quarter of the birds make it to ten.

Swans are generally known as monogamous, but they don’t always mate for life. Stotz quotes one English study where the “divorce rate” was about 3 percent a year for unsuccessful breeders. “Given that they are typically at least three when they start breeding and have an average life span of six to seven years,” he says, “that would mean in the wild about 90 percent would have only one mate.”

Art accompanying story in printed newspaper (not available in this archive): photo/Kanae Hirabayashi.