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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 & Patterns
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 sparkling 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.
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.
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.
Behaviors related to cleaning and maintaining feathers in good condition. Sometimes loons show their greatest acrobatic talents while bathing. They will flip, dive aggressively, smack the water hard with their wings, and essentially look like a loon that’s possessed. They likely do this to force water through their feathers to extract dirt and feather parasites. Loons are diving birds and thus must take meticulous care of their feathers to maintain their water repellency.
Loons spend much of their life on the ocean and in cold water lakes. Their waterproof feathers prevent the water from reaching their skin and causing hypothermia. The waterproof outer feathers produces an insulating layer of air between them and the skin to further help keep the loon warm in cold water. Preening behaviors involve extracting oil from the uropygial gland near the base of the tail and working the oil through all of the feathers. To reach their belly and side feathers, loons will roll to one side. They will rub their heads on their backs to waterproof head feathers.
Behaviors that improve the loon’s comfort, include stretching muscles as with a wing stretch or a foot waggle. During a wing stretch the loon rises out of the water and stretches both wings back and flaps them. A foot waggle is when a loon stretches a foot out of the water and shakes it.
Adult loons give four basic calls: wail, tremolo, yodel, and hoot.
Loons hunt for fish and crustaceans under water. They will sometimes begin a foraging excursion by lowering their head into the water and “peering” for their prey. When a prey item is spotted, they will dive and swim after their quarry. Loons are skillful and agile swimmers and use their large webbed feet for propulsion. They hold their wings close to their bodies. When they catch their quarry, they come back to the surface. A loon may spend 5-10 minutes trying to orient its prey so it can be swallowed head first.
Mated pairs spend much of their time together especially early in the breeding season. They are often seen swimming side-by-side and making short dives together. Sometimes as they swim together they will turn their heads away from each other and exhibit bill-dipping, signs of non-aggression.
Aggressive encounters seem to usually involve attempted territorial take-over of a breeding area or a feeding area. Early in the season, a male or a female will invade a territory and test the pair bond of the resident pair. If the intruder is a male, it will face-off with the resident male. If the intruder is a female, it will face-off with the resident female. Occasionally a pair will intrude and the four will face-off together; this is especially common on large lakes with adjacent territories. Later in the breeding season, a single adult or pair will face-off with any intruding loon in defense of its young. Even lone non-breeding loons occasionally have aggressive encounters over popular feeding areas. This type of encounter is usually resolved quickly with the “loser” moving on.
The loon’s primary weapon is its bill. Therefore most aggressive postures and movements involve threatening the opponent with the bill. A typical aggressive encounter sequence involves the loons coming together in the middle of the lake. They will circle swim, peer underwater, and jerk their heads. They will point their bills directly at their opponent(s). All birds involved will occasionally jerk or splash dive. While underwater the loons attempt to stab their opponent with their bills.
The outcome of most encounters involves the expulsion of the losing loon (often the intruder) from the territory. The losing loon will either dive and swim out of the territory or fly off the lake. On rare occasions, loons may be injured or killed in aggressive encounters and will not be able to leave the lake. When injured, they often crawl on shore to avoid drowning or to evade the attacking loon.
Around the Nest
As a loon pair begins thinking about nesting, they will scout the shoreline of their lake for suitable places to nest. Once the nest site has been selected the pair will build the nest using mud, leaves, grasses, or any material surrounding the nest site or on the lake bottom. They will copulate on the nest and soon the female will lay one to two (rarely three) eggs. The adults will take turns incubating the eggs and nest exchanges are usually followed by egg turning prior to settling onto the eggs. The eggs can withstand being exposed for extended periods of time when the weather is dry and warm.
Disturbance Near the Nest
If you (or potential predators) approach a loon nest, the behavior of the incubating loon will tell you if you are too close. First, the loon may raise its head in an alerted position to better view the disturbance.
If you continue to approach, the loon will put its head down to the water and flatten its body in a hang-over posture to try to hide from view. This indicates that you are too close! If the loon perceives that danger continues to approach, it will slip off the nest and into the water. If the loon is startled, it will flush abruptly and may kick the eggs out of the nest.
A loon that is in the water and near the nest will often remain low in the water with only the head and sometimes part of the back above the water’s surface. It is trying to look small and out of view while it keeps on an eye on your activities near the nest.
If you approach the nest too closely, a loon in the water may penguin dance and try to lead you away from the nest. This is their most extreme reaction to human presence and means you are much too close to the nest (or chicks later on). This is not the time for taking pictures; you should leave the area immediately.
As soon as a chick dries out after hatching, it is ready for the water. It can swim and make shallow dives even at this young age. It can be weary work keeping up with the adults; therefore young chicks are often seen backriding. This also serves to keep the chick warm and protected from flying and underwater predators. An adult will also wing tuck a chick which serves these same purposes.
Chicks are semi-precocial meaning they can leave the nest immediately and swim on their own. However, they are dependent on the adults to be fed until they learn to hunt on their own. Both adults will feed the chicks.
Fall Flocking & Migration
Towards the end of the breeding season, loons will begin to gather in small groups. Loons that did not breed or that were unsuccessful in hatching or rearing chicks likely group together first. By October, large flocks of fifty or more loons can be observed particularly on large lakes. Loons will migrate singly or in loose groups but don’t travel in tight flocks as do other birds. Adult loons will migrate earlier than the chicks. For the chicks, it is a race against time. They must grow strong enough to leave their natal lake before the winter ice forms.
As a migratory bird, loons are protected by the Migratory Bird Act which prohibits the harassment or killing of loons, eggs, or chicks. It is also illegal to possess loon feathers, eggs, nests, or entire birds. Midwestern loons spend the summer on northern inland lakes and head south or east in the fall to spend the winter on the Atlantic coast or in the Gulf of Mexico. Western common loons overwinter on the Pacific coast from Alaska to the Baja peninsula and in the Gulf of California.
Visit the USGS Common Loon Migration Study website to view the migration paths of Midwestern and New England loons.
Annual Cycle or Phenology
Phenology is the study of periodic biological phenomena, such as flowering, breeding, and migration, especially as related to climatic conditions. Common loons arrive on Wisconsin lakes as soon as the ice leaves in mid-to-late April. Most loons in Wisconsin are nesting by mid-to-late May, with eggs beginning to hatch one month later in mid-to-late June. Some pairs that begin nesting later, or who lose their first nest and try a second time, will have eggs hatching into early July. Loons typically lay only two eggs per nesting attempt. Nests with three and even four eggs have been documented, but are rare.
After chicks hatch, they stay on the nest for up to one day until the adults call them off. Once on the water, they are taken to a nursery area, which is usually a secluded bay or protected shoreline. Adult loons feed and protect the chicks until they can dive and catch their own food at approximately eight weeks of age. Adults often leave the chicks and form pre-migratory flocks in early August. Adults begin flying south in late August and early September.
Chicks stay on the nesting lakes, feeding and taking their first test flights, until nearly ice-over. One day, they start running across the water, take flight, and head south, where they will stay until they are three years old. Most chicks return to their nesting lake (or one close by) when they have attained the adult’s black-and-white feathers at the age of three. However, current research is finding that many loons do not acquire a nesting territory until they are six years old, so most end up swimming around our lakes, waiting for an open territory.
Loon Breeding Habitat
Common loons are widely distributed in northern Wisconsin and the Upper Midwest, but not all lakes have loons on them. While there are no criteria that guarantee a lake will have nesting loons, the following are important characteristics.
Loon Wintering Habitat
In the fall, loons migrate south to spend the winter on the ocean along the Atlantic coast and the northern coast of the Gulf of Mexico. There they feed and molt in coastal areas and do travel some distance offshore. Little is known about the wintering ecology of loons and there are many questions we would like to have answers for such as: Do individuals return to the same wintering sites each year as they do on the breeding grounds? Do females and males use different sites? How does weather (and large storms like hurricanes) affect the winter distribution of loons? Do loons aggregate and, if so, where? Do loons select certain areas for specific resources?
Loon Migration Habitat
Common loons frequently use lakes not used during the breeding season as stopover points during migration. These lakes are important as staging areas and as feeding and resting locations during migration. The Great Lakes and large inland lakes and reservoirs throughout the eastern US and Canada play an important role in maintaining the loon population. Without quality stopover sites, loons may have a difficult time traveling between their breeding grounds and their wintering sites on the Atlantic Ocean and Gulf of Mexico. Little is known about loon migratory habitat and therefore is an important subject for future studies.
How much does a loon weigh?
The average weight of a common loon in the Great Lakes area is ten pounds.
How much does a loon eat?
Loons eat approximately two pounds of fish each day.
How fast can a loon fly?
In flight, loons flap their wings about two hundred times per minute and reach speeds of approximately seventy miles per hour.
How small of a lake will a loon use?
Minimum lake size for nesting loons is reportedly ten acres, but on rare occasions loon nests have been found on smaller lakes.
How long do loons live?
The average age of a common loon at first nesting is six years. A loon can live for approximately twenty-five to thirty years.
What do loons look like?
The common loon measures about 30 inches from head to tail, has a five-foot wingspan, and weighs six to thirteen lbs. During the breeding season, the loon has a black iridescent head, red eyes, and a white necklace. Its back and wings are black with white spots, and its underside is white. Loons float low on the water and dive frequently.
What are the different loon calls?
Adult loons give four basic calls: wail, tremolo, yodel, and hoot.
Are loons protected by law?
Yes. The Migratory Bird Treaty Act protects loons and all migratory non-game birds from harassment. In Wisconsin, please report intentional loon harassment to the DNR at 1-800-TIP-WDNR.
Are there different species of loons?
There are five species of loons: the common loon, Arctic loon, Pacific loon, red-throated Loon, and yellow-billed Loon. Only the common loon nests in the lower forty-eight states. The other four species nest in Canada, Greenland, Alaska, northern Europe, and Russia.
How did the loon get its name?
The scientific name is Gavia immer. Gavia refers to the seabirds and immer comes from the Swedish root emmer or blackened ashes of fire. The common name “loon” likely comes from either the English word lumme meaning lummox or awkward person or the Scandinavian word lum meaning lame or clumsy. Either way, the name refers to the loon’s poor ability to walk on land.
How many loons live in the Midwest?
Wisconsin lakes are the summer home to approximately 4,000 adult loons. Minnesota has about 12,050 loons, and Michigan has more than 650.
Do loons mate for life?
Banding records show that loons often return to the same lake each year. However, mates probably don’t winter or migrate together and return to the same lake independently. Loons do occasionally switch mates and are more attached to their lake than to each other.
Where do loons nest?
Loons build their nests at the water’s edge because they have difficulty walking on land. Loons prefer to nest on islands and in backwaters protected from wave action. Often, they use the same nest site each year.
How many eggs do loons lay?
Most loon nests have two eggs, although some may have one or, rarely, three eggs. Loons may lay a second clutch of eggs if the first nest is destroyed. Loon eggs are 3 inches long with an olive green shell with dark spots.
Why do chicks ride on their parents’ backs?
Chicks ride on their parents’ backs during the first three weeks of life. Here, they conserve energy, stay warm and are protected from predators like northern pike and bald eagles.
Do loons move their chicks across land from one lake to another?
Yes, sometimes adult loons will lead or call their chicks from their nest lake to a forage lake. This seems to happen most often when the nest is on a small lake close to a much larger lake where the adults prefer to feed.
What are the common predators on loon eggs and chicks?
Loon eggs are eaten by raccoons, otter, mink, gulls, crows, ravens, and eagles. Loon chicks are most often eaten by eagles, muskie, northern pike, and snapping turtles.
How long does it take for a loon to reach adulthood?
Loons acquire their full black-and-white plumage at about three years of age, but often don’t begin nesting until they are five.
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