Body Form And Plumage of Common Loons
The Common Loon in its summer breeding plumage is a striking bird with a black-and-white checkered back, iridescent black head, black bill, red eyes, a prominent white "necklace" marking at the back of the neck, and a much smaller white “chinstrap” marking at the throat. The white feathers of the belly and wing linings are present year-round, but loons have a basic winter plumage of gray feathers. Immature loons resemble adults in winter plumage from a distance.
Male and female loons look alike, although males are generally about 20% larger than females. Loons are large-bodied, weighing from 2.7 to over 6.3 kilograms and measuring almost a meter from bill tip to outstretched feet. The bill is large, averaging 75 mm in length, and is black in color throughout the year. In flight, loons can be recognized by their humpbacked profile, with head and neck held low and feet projecting beyond the tail.
The skeleton and muscular systems of a loon are designed for swimming and diving. The legs are placed far back on the body, allowing for excellent swimming in water but making them ungainly on land. The bones of loons are more dense than bones of most flying birds. These heavy bones make loons less buoyant and help loons to dive. The loon's large webbed feet provide propulsion and steering underwater. A loon’s wings are held tightly against the body while underwater, and loons do not “fly” underwater like penguins.
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