Boom in Mute Swans Spurs Calls for Culls

James Owen in Britain
For National Geographic News

June 21, 2004

The massive mute swan is creating ripples on both sides of "the
pond." In both the U.S. and Europe, groups want to control booming
swan populations to prevent them from overwhelming other species.
Others say the bird is being made a scapegoat for environmental
damage caused by humans.

The mute swan is an unmissable bird. Beautiful, graceful, spotless white, and awesomely large, it draws admiring looks in lakes and parks across Europe and North America. But some people are rather less enamored. So much so that some in the U.S. even want the birds culled.

The trouble is that mute swan populations are booming on both sides of the Atlantic, and at the expense of much other wildlife, say government agencies, scientists, and sport fishers.

With wingspans topping out at nearly 8 feet (2.4 meters), the aggressively territorial species is one of the world's biggest flying birds.

In Britain the mute swan was considered a domesticated bird until the 20th century, having first been kept by 12th-century English kings who made them the centerpiece of sumptuous royal feasts. Yet wild populations have increased 250 percent since the 1960s, according to breeding-bird surveys in Britain.

A protected species, the mute swan got a further boost in the mid-1980s. Anglers were banned from using toxic lead weights, which swans were found to swallow while feeding. The ban fueled a large rise in swan numbers on rivers, particularly spring-fed, chalk rivers in southern England, which are protected under European legislation that covers key wildlife habitats.

But fly-fishers claim mute swans are stripping these rivers of water crowfoot, an aquatic plant crucial to trout and the insects they eat.

"Many invertebrates use water crowfoot as cover and are much less successful if there isn't any," said Robin Mulholland, chairman of the Wiltshire Fishery Association, which represents the region's chalk river fly fishers. "It's also important in terms of defining territories for trout."

Mute swans—which each eat upward of four and a half pounds (two kilograms) of water crowfoot per day—may also be jeopardizing one of Britain's rarest mammals, the water vole, said Allan Frake. Frake is a biologist with the Environment Agency, the main government agency responsible for protecting the environment in England and Wales.

"Swans eat the [water crowfoot], the water level drops, and then stoats [a type of ermine] work [the water voles'] holes in the riverbank," he said.

From Europe

Similar concerns exist in the United States, where mute swans were first introduced as ornamental birds from Europe and Asia in the 19th century. At least 14,000 mute swans now live along the U.S. Atlantic coast alone, according to the U.S. Fish and Wildlife Service.

Speaking last year, the service's director, Steve Williams, said: "Wildlife biologists and refuge managers have significant concerns about the impacts of growing populations of non-native mute swans on native birds and their habitats. Mute swans can cause extensive habitat degradation in wetland habitats."

In the Chesapeake Bay some 3,600 birds consume 10.5 million pounds (4.8 million kilograms) of submerged aquatic vegetation (SAV) each year, said Jonathan McKnight. McKnight is the Maryland Department of Natural Resources (DNR) biologist responsible for the state's response to invasive species.

He said water plants targeted by the swans—including eelgrass, wigeongrass, and sago pondweed—act as important nursery areas for fish and invertebrates.

"SAV beds are the basis of a complex web of life in Chesapeake Bay," McKnight added. "They are the homes of seahorses and pipefish, of crabs and juvenile fish, of ducks and herons."

These beds have already been affected by declining water quality, and now mute swans threaten those that remain, McKnight said.

Their aggressive behavior has also led to the displacement of native birds from nesting and feeding areas, he said. "Mute swans are responsible for driving the last remaining colony of black skimmers from Chesapeake Bay."

The Great Lakes may face similar pressures, with Canada-based scientists suggesting mute swan populations are growing by up to 30 percent each year on Lake Erie and Lake Ontario. And in Wisconsin conservationists fear efforts to reintroduce the trumpeter swan could be undermined by the presence of its larger, more aggressive cousin.

Cull Plans

The U.S. Fish and Wildlife Service is seeking to authorize a controlled cull of mute swans in various states. Maryland plans to kill around 3,000 mute swans over the next two years.

However, all swans are currently protected under the U.S. Migratory Bird Treaty Act (even though the mute swan is non-migratory). But a bill is currently being advanced in the U.S. Congress to remove the mute swan and other invasive species from the list. U.S. animal welfare groups, for their part, argue that mute swans don't pose a significant threat to wetland habitats.

In the case of the Chesapeake Bay, environmental pollution—such as from runoff from intensive chicken farming—is to blame for lost wildlife, according to the Fund for Animals, based in New York.

The fund's president, Michael Markarian, said: "[Maryland's] complaint against the birds is not that they are causing problems now, but that they might cause problems in the future. The DNR is offering a solution in search of a problem, and it is managing wildlife by trying to predict the future. It's not scientific—it's voodoo management."

In England factors such as climate change and nutrient enrichment via sewage treatment plants may also harm river systems that support mute swans. But that shouldn't divert attention from the problems swans cause, Robin Mulholland said.

"Someone's got to stand up and say, 'This is how many [swans] we want, and we've got to keep populations at that level,'" he added. "It sounds hopelessly optimistic, but we live in a man-made environment, and we've got to begin to talk about controlling populations of certain protected species, otherwise they get out of hand."

The mute swan's soaring success could also signal its swan song.

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