Every fall, Common Loons gather on Lake Mille Lacs to feed in preparation for their migration south. On a good day you might count hundreds of loons. Other lakes experience the same thing. And, of course, loons nest throughout the northern half of the state. Common Loons are our state bird.
What if the loons arrived at Mille Lacs or any other lake in the state and found none of the small fish that make up their diet? They wouldn't stay. If that situation -- lack of food -- prevailed, loons might be no more than casual visitors. We'd have no nesting on those lakes, no loon calls wavering through the night. If the lower components of a lake's food chain disappeared, the animals higher on the chain would disappear as well.
How could this happen? Well, if you read the Sunday StarTribune "Outdoors" pages in the sports section you saw Doug Smith's report on the rapid growth of Zebra Mussels in Lake Mille Lacs. That invasive species is being counted in thousands per square foot in parts of that lake. They multiply in amazing and frightening numbers. Zebra Mussels take their nourishment from the water, filtering it through their systems to capture algae. Algae is food for zooplankton, which in turn is food for small fish. Loons and certain other species of waterfowl eat small fish.
The chain reaction started by the mussels could move all the way up to birds.
I asked Carrol Henderson, chief of the Minnesota DNR non-game section, if mussels are a possible problem for birds.
"I suspect that certainly could be a problem," he said, "especially in a situation like they reported for Mille Lacs. The dominance of the Zebra Mussels on water chemistry and the food chain is likely to be so overwhelming that it would affect the abundance of various small fish that comprise the diet of loons.
"We're entering an era of great unknowns whenever Zebra Mussels take over in a lake," Henderson said.
The mussels currently are found in about 20 other lakes, rivers, and waterways in Minnesota, including Lake Minnetonka. The mussels attach themselves to anything and everything, including boats, anchors, anchor ropes, and strands of vegetation that might be tangled around outboard motors or boat trailers. Fishermen are being urged to carefully inspect and clean motors, boats, and trailers before moving from one lake to another. Once the mussels find a new home, there is no known way to remove them.
What gets removed is the known food chain, with our loons and other bird species at the top.
Below, a Common Loons feeds a small fish to one of its chicks.