There are only five species of loon on our planet and all five can be found in North America. They belong to an order of primitive birds that dates back over 70 million years; fossil records show that loon relatives lived during the latter part of the Cretaceous period. Since they are so ancient you will find the loons on the first page of all avian field guides and natural history books that organize the birds in taxonomic order.
The Common Loon (Gavia immer) breeds on large lakes in Alaska, Canada, Greenland, Iceland and the northeastern U.S. states. (It does not currently breed in Connecticut.) Its gorgeous black head, throat and bill contrast sharply with a collar of thin white lines and a black-and-white checkerboard back. But in the fall it will molt from this distinctive summer breeding plumage to a drab gray head and back with white undersides. Its daggerlike bill will pale. You may observe loons sporting this duller plumage in Long Island Sound during the fall and winter months when they migrate to our coastal waters.
Both the Common Loon and the Red-throated Loon (Gavia stellata) inhabit the cold waters of our shoreline over the winter. You may see a loon lower its face under the water as it searches for its next meal. Once it spots its prey, it will dive and give chase. (Fish are the main course of a loon’s diet, but crabs, shrimp, and other aquatic creatures are also eaten.) Don’t be surprised if the loon stays submerged for a minute or so.
On occasion they are also found on wet road pavement. Since loon legs are placed so far back on their bodies, it is very difficult for them to walk on land, and impossible for them to take flight from it. A loon, mistaking a rain-slicked road or parking lot for a body of water, becomes helpless if it lands. Human assistance is usually required, first to treat any possible injuries, and second to transport the bird to either a large lake or the ocean. Loons may require up to a quarter-mile of open water to become airborne.
A more serious problem faces these magnificent birds. Studies have been conducted in Canada and the northeastern United States that document an ongoing problem with mercury poisoning in loons breeding in northeastern lakes. Much of the mercury originates from coal-fired power plants to the west. It reaches New England’s northern lakes on the wind, or in rain or snow, and accumulates in the lakes’ fishes and other aquatic creatures. Those at the top of the food chain, such as loons, receive the highest accumulations of mercury and over time show signs of mercury poisoning. Mercury affects the nervous system, especially in young loons, and has been associated with loon reproductive failure.
Other very real threats to loons include acid rain, which kills off the plankton that is the base of a lake’s food chain, and lead poisoning, another cause of mortality when loons ingest carelessly discarded lead fishing sinkers.