Mention the phrase "invasive species" in the presence of a biologist and she'll usually respond with elevated blood pressure, a knitted brow, and a less-than-friendly stare. And for good reason; all manner of mischief and mayhem detrimental to native habitats and wildlife typically ensues once uninvited genies get out of their bottles, so to speak.
There are countless cases from around the globe and the problem is ongoing, but even locally we have examples. By now everyone is at least somewhat aware of the deleterious effects from the arrival of purple loosestrife, leafy spurge, spotted knapweed, Eurasian milfoil, zebra mussels, Asian carp, and the impending appearance of emerald ash borers. One species not on most North Dakotan's list of exotics, however, is the mute swan (Cygnus olor). That might be about to change.
There have been a tiny handful of mute swan sightings in the state of North Dakota over the years but two have occurred within just the last 10 days. Three birds were spotted at the West Fargo lagoons by Dean Riemer on June 24. Two days later a couple spotted a single bird in a slough near Churchs Ferry.
What makes this large, graceful, white bird so unwelcome? Foremost is the birds' tenacious behavior, both toward native species and to humans. The Minnesota DNR says, "Mute swans are very aggressive even toward people. They chase water birds including loons, and can keep those birds from nesting." There are documented cases of mute swans killing native waterfowl. Terres (1956) wrote "vigorously defends nests and young from intruders, may attack dogs and even people, can be dangerous to children." Not exactly a ringing endorsement.
Also, mute swans are voracious consumers of aquatic vegetation, feeding in such a manner that native habitats are at risk of destruction. At Birds of North America Online, Ciaranca, Allin, Jones (1997) wrote, "Overgrazing can cause a functional reduction of aquatic habitat, adversely affecting the food web." Again, not an attractive attribute for a species foreign to North Dakota, known around the country as America's duck factory.
Mute swans are native to Eurasia where the birds have been semi-domesticated at least as far back as the 12th century. They are large and white but with orange knobby bills, which separates them easily from our native tundra and trumpeter swans, both of which have black bills. Where native swans are more linear and seemingly alert, mute swans could be considered curvy and somewhat shy with their heads usually angled down.
I learned a word while researching mute swans: busking. This means assuming the threat posture by arcing the neck into an S-shape and holding secondary feathers up and over the back in a pose most of us would recognize as that depicted on merry-go-rounds.
There exists a handful of populations in North America, all derived from escaped or released birds of European origin starting in the 19th century. Mutes along the East Coast, mostly centered on Chesapeake Bay, are expanding. One subscriber to North Dakota's online bird discussion group lives in Maryland and recently wrote, "(mute swans) are a horror story out here on the East Coast. They need to be eradicated (in North Dakota) ASAP before they start colonizing."
Of more import to North Dakotans is the burgeoning population in the state of Michigan. First introduced there in 1919, mute swans have tripled in number over the last 10 years, currently there are nearly 20,000. The Michigan DNR has set a goal to reduce their mute swan numbers to "less than 2,000 by 2030."
Michigan is very likely the source of sightings in our area, including those in Minnesota, whose DNR labels the bird "a regulated invasive species."
The recent reports did not go unnoticed by North Dakota Game and Fish Department officials. "It's something our waterfowl guys are aware of," said Jeb Williams, Assistant Chief of the Wildlife Division.
Still, recognizing a problem and doing something about it often requires at least some diplomacy. After all, the removal or killing of animals is not usually the image wildlife officials want to present to the public. "The best way to help with that is education," says Williams.
Once aware of the deleterious effects exotic species have upon local wildlife, an informed public usually welcomes control. Ciaranca, et al. warns, "As the Mute Swan spreads throughout the continent, close watch should be kept on its displacement of native waterfowl species and its effects on North America's wetland habitats."