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 around 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.
In its winter plumage, the Common Loon is gray above with a white breast, belly and wing linings. Their eyes remain red during the winter.
Chick Plumage Sequence
Natal Down- When loon chicks first hatch they are covered in dark downy feathers and have white bellies. They are often seen riding on their parents backs (usually for the first 7-10 days), which helps with temperature regulation and protection from predators.
Brown Down- At around two weeks of age, they molt into a second downy plumage that is a lighter brown and they still have a white belly.
Between 3-4 weeks of age, their body elongates and their bills also begin to lengthen.
Emerging Juvenal- By 5 weeks of age they start to look a little unkempt as their contour feathers are starting to come in. It takes approximately 3 more weeks until all of their down feathers have been replaced.
Full Juvenal- At 10 weeks of age they have the characteristic shape of a loon and they will retain this plumage and their brown eyes until they start to molt into breeding plumage at 2.5 years old. Around this time the juvenile loon will also begin practice flights and is usually completely fledged (able to fly) by 12 weeks of age. Immature loons resemble adults in winter plumage but their feathers have a scalloped pattern on the edges.
All Chick Plumage Sequence photos courtesy of Kittie Wilson
Body Form of Common Loons
Photo courtesy of Brian Reilly
Male and female loons look alike, although males are generally about 25% larger than females. Loons are large-bodied, weighing from 7 to 15 pounds and measure almost a meter from bill tip to outstretched feet. The bill is large, averaging 2-3” in length, and is black in color during the breeding season. 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, so loons do not “fly” underwater like penguins.