How Big is a Loon?

The Common Loon measures about 30 inches from head to tail and has a 5-foot wingspan. Adults weigh 6 to 13 lbs. with the male generally being larger than the female in a pair.

Plummage (feather colors and patterns)

Breeding Season (Summer)

During the breeding season, the adult loon has a black iridescent head (that may look greenish in the sun), red eyes, and a white necklace and chin strap. Its back and wings are black with white spots, and its underside is white. The black back with white spots matches the sunlit spots sparking on the surface ripples of a lake. The white underside helps the loon blend in with the bright sky from the perspective of underwater predators. Toward the end of summer, adult loons begin molting into their winter plumage (called the pre-basic molt).

Non-breeding Season (Winter)

At the end of the breeding season, the first signs of molting show up on the face around the bill as the black feathers are lost and replaced with white ones. This fall molt is called the pre-basic molt.  The black feathers on the back of the loon will be replaced with brown ones. They retain their flight feathers and continue to molt on migration to the wintering grounds on the Atlantic Ocean and the Gulf of Mexico. The loon’s throat and chin will become white to match the belly. The back will be grayish brown and the eyes will turn brown. Before the loons return to northern lakes from their wintering grounds, they will molt back into their breeding plumage (called the pre-alternate or pre-nuptial molt). They are completely flightless during this time.

Differentiating Adults, Immatures (Sub-adult), and Chicks

Immature Common Loon

Immature or subadult common loons are rarely seen on northern lakes during the summer. These are young loons that are a year or two old that typically do not return to the breeding grounds until their third summer when they attain the black and white plumage of an adult. Immatures are the same shape and size as an adult loon but the plumage is gray or brown with a solid white throat and belly and lacking the black-and-white striped necklace. They look very similar to an adult with non-breeding or winter plumage. Behaviorally they usually act like a non-breeding lone adult and are most frequently found on large lakes away from territorial pairs.

Loon Chicks

Newly hatched loon chicks are black downy fluff balls. They can dive soon after hatching but have trouble staying submerged for long. They often pop up like corks and sometimes appear to have trouble getting their buoyant bottoms under the water’s surface.

After a couple weeks, chicks molt into brown-grey downy feathers. From 4-12 weeks, the downy feathers are gradually replaced by brown-grey contour and flight feathers. Once they attain their flight feathers, chicks make their first attempts at short flights. In the fall, a chick may be difficult to differentiate from an immature bird.

Differentiating Loons from Similar-looking Species

Common loons are sometimes confused with other waterbirds found in the same aquatic habitats. Loons are diving birds and therefore their legs are positioned farther back on the body than on geese or ducks. Loons have a long dagger-like bill unlike the more rounded bills of ducks and geese. Loons are probably most often confused with mergansers, a diving duck with a pointed bill and similar plumage characteristics. The common and red-breasted mergansers are about half the size of a loon and have a thinner, shorter bill. Both mergansers have crests and lack the speckled white on black plumage of a loon. Loons have a necklace with alternating vertical black and white stripes versus the solid white necklace of the male common merganser. Mergansers often have more chicks than a loon.

CANADA GOOSE – larger than a loon; sits higher in the water; black neck but no necklace stripes; solid white cheek patch; does not dive.

RED- BREASTED MERGANSER –half as large as a Common Loon; similar silhouette; sexes differently colored; females are dull gray with rusty head; males have a green head, white neck, and rusty breasts; both sexes have crests on the back of the head and bright orange bills.

COMMON MERGANSER – similar to Red-breasted Merganser, but lacks rusty breast; sexes differently colored; males have bright green heads, females have rusty red heads; bright orange bill.

DOUBLE-CRESTED CORMORANT –similar in size and shape to a loon; sits low in water; body completely black except for orange throat pouch; when swimming points its head and bill upward.

WESTERN GREBE – nearly as large as loon; similar silhouette; sits low in water; solid black body, long, white neck, and pale, yellow bill.

Loons can also be identified by their behavioral cues and vocalizations.