Loons are large birds with primarily black or grey plumage, with characteristic white markings which can be used to differentiate between species. Some colour variation exists among species - for example, the red-throated loon has a red throat. At first glance, loons look similar to large ducks, but they belong to a different family. They can be readily distinguished from ducks by their long bodies, pointed bills and the position of their feet - a loon’s feet are located much farther back on its body. The positioning of loons’ feet makes them good swimmers and divers, but awkward on land. Loons also have the ability to change the specific gravity of their body by exhaling air and compressing their feathers; this allows them to float high on the water, or sink down low with only their heads showing above the surface. Their swimming ability and associated adaptations are related to their ecology- all loons actively pursue and catch fish underwater.
Loons are common in the Arctic, but can also be found throughout North America and northern Europe. Although loons are most frequently observed in the freshwater environments where they breed, their annual cycle alternates between salt and freshwater. In winter, loons from the Arctic migrate to areas along the coasts of North America as far south as Mexico, congregating in feeding flocks.
Breeding loons are territorial, and pairs aggressively defend a carefully chosen nesting area. Most require lakes big enough for 100 m take-off and landing zones, and waters that are clear enough to allow them to search for fish. Loons are generally considered good indicators of an ecosystem’s health because they are very susceptible to pollution.