Common loons are large swimming birds with long bodies (70 to 90 cm long, 1.6 to 8.0 kg) that sit low in the water. They have straight, thick, "daggerlike" bills that are black in the breeding season and gray during the rest of the year. The plumage of loons is black, white and gray. During the breeding season, common loons have a black head with a white and black striped necklace, and a checkered pattern on their back. During the winter, they are evenly gray on the head and back, with a white neck and underside. The common loon can be distinguished from other loons by its unique plumage patterns during the breeding season and black bill. During the winter, common loons can be distinguished by the indentation of the white neck color at mid-neck. Common loons are also larger than most loon species, except yellow-billed loons.
Male and female common loons look alike, though the males are usually larger than the females. Young common loons look similar to winter adults, but have more white on their head and back. They keep this juvenile plumage through their first summer. ("Field guide to the birds of North America, Second Edition", 1987; Peterson and Peterson, 2002; Robbins, et al., 2001)
This species is most abundant in Canada and the Northern United States. Common loons breed on lakes and other waterways from western Greenland west across Canada and the northernmost United State, including Alaska. They winter along both coasts of North America as far south as Baja California and Texas. There is a breeding population on Iceland, and the species is a frequent winter visitor to the western coasts of Europe.
Loons nest on lakes and large ponds. Weather restricts habitat selection, because loons cannot nest on frozen water. They prefer to nest offshore, on islands, islets, or floating mounds of vegetation in shallow water. In winter, loons migrate to shallow coastal marine habitat.
Common loons breed once per year in the summer. They are thought to be monogamous, remaining with the same partner for life. Male and females arrive on the breeding territory together early in the spring. They establish a territory of 60 to 200 acres, which they patrol regularly. Common loons use physical displays and vocalizations to defend their territory and for courtship. For example, a loud yodeling call is used by males to let other males know that their territory is occupied. Following courtship displays, the male and female may swim to shore, where copulation occurs. To copulate, the male stands on the female's shoulders, with his head extended over and beyond hers. ("", 2001; Stokes and Stokes, 1983)
Common loons breed once per year in the spring and summer, beginning at age 2 or 3. The male and female build a nest about two feet wide and made of soil, grasses, moss or plant matter. The nest is usually in a sheltered location near deep water so that the male and female can swim to and from the nest without being seen by predators. Nests are usually built on islands or peninsulas. When the nest is finished, the female lays 1 to 3 (usually 2) brown eggs, one to two days apart. The male and female both incubate the eggs, beginning after the first egg has been laid. Incubation lasts for 29 days. The first chick hatches up to a day before the others. They stay in the nest for a day or two after hatching, and then leave the nest with the parents. They spend the 2 to 3 months swimming around the territory with their parents, sometimes riding on the back of one parent. The chicks are able to dive short distances at two days old, and are able to fly at two to three months. Once they are able to fly, the young loons can become independent of their parents. ("", 2001; Stokes and Stokes, 1983)
During incubation, male and female common loons take turns incubating the eggs and protecting the nest. After hatching, the chicks leave the nest with the parents. The parents feed the chicks whole food every hour from the time of hatching until they are up to three months old. They also protect the chicks from predators by vocalizing and swimming away from the predator to distract it from the chicks. Parents often carry the chicks on their back during the first few weeks of the fledging period. If the chicks are cold, a parent may return to shore with the chicks, where it shelters them under its wing. Chicks remain with their parents for up to three months, until they are able to fly. (Stokes and Stokes, 1983)
Common loons are thought to be relatively long-lived birds. However, there is little information available about common loon survivorship. The oldest known wild common loon lived at least 9 years. ("", 2001; "USGS Upper Midwest Environmental Sciences Center", 2003)
During the breeding season, most loons are found in breeding pairs. However, unpaired individuals and pairs that did not raise chicks may stay together in small flocks. The breeding territory of loon pairs ranges from 0.24 to 0.81 square kilometers in size.
Common loons are migratory. They leave their breeding grounds in the fall, beginning in September. They migrate during the day, either alone or in small flocks of up to 15 loons. During migration, loons may spend the nights in flocks of several hundred individuals on large inland lakes, but they split up again in the morning into smaller groups. On their wintering grounds, individuals defend small feeding territories of 0.04 to 0.08 square kilometers during the day, but they flock together at night.
Common loons are excellent swimmers. Their legs are placed very far back on their bodies, making them very powerful underwater swimmers. However, this arrangement also makes walking very difficult for these birds. ("", 2003; "", 2001; Stokes and Stokes, 1983)
Common loons use visual displays and vocalizations to communicate. Stokes and Stokes (1983) counted six different visual displays and five types of calls used by common loons. These calls and are used to attract mates, defend territory, signal danger and to communicate between flock members and family members. (Stokes and Stokes, 1983)
Loons eat fish and other aquatic animals, including crayfish, shrimp, leeches and some aquatic vegetation. Minnows are good-sized food for young, which also eat insects occasionally.
Loons are visual predators, locating fish by sight and diving deep to catch them. They generally hunt in water 2 to 4 meters deep. Because they rely on sight, clear water is critical to common loons. Adult loons ingest most of their food items underwater where they catch them. They bring larger items to the surface before eating them.
Loons drink water by scooping it up with their bill and tilting their head back in order to swallow. (McIntyre and Barr, 1997)
Adult loons have few known predators, but may be vulnerable to large marine mammals such as sea otters and large raptors, such as bald eagles and ospreys. Gulls, crows, ravens, bald eagles raccoons, skunks, minks and weasels, snapping turtles and large fish are predators of loon eggs and chicks.
Loons avoid predation by nesting on islands, where ground-based predators are less common. When approached by a predator, loons sometimes attack the predator by rushing at it and attempting to impale it through the abdomen or the back of the head or neck. ("", 2001; McIntyre and Barr, 1997)
Common loons are provide food for their predators. They are also host to at least forty different body parasites. Most of these are cestodes and trematodes.
Because common loons eat fish, they are viewed by some people as competition for fishermen.
Common loons are a source of food to the Cree Indian tribe of Canada. They were once hunted for sport, and are now an important symbol of wilderness to many people.
Common loons are threatened because their habitat is being destroyed. Loons are very sensitive to human disturbance, including recreation or development on their lakes. They are also threatened by pollution, such as mercury and other heavy metals that build up in the loons' bodies and slowly poison them. Acid rain is another pollutant that kills the aquatic plants and animals that many fish eat. This means that there are less fish for the loons to eat.
Oil spills are also deadly to loons. When loons become covered in oil, they are unable to fly, dive or swim. Loons can also be poisoned by accidentally eating lead fishing lures that are left in lakes and by getting tangled up in fishing nets.
Common loons are not federally endangered or threatened. However, they are specially protected in some states, including Michigan, where they are listed as threatened. They are also protected by the U.S. Migratory Bird Act. ("", 2001)
Kari Kirschbaum (author, editor), Animal Diversity Web.
Roberto J. Rodriguez (author), University of Michigan-Ann Arbor.
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