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Gavia immercommon loon(Also: great northern diver)

By Kari Kirschbaum and Roberto J. Rodriguez

Geographic Range

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.

Habitat

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.

  • Range depth
    0 to 80 m
    0.00 to 262.47 ft

Physical Description

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 barred 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, excluding yellow-billed loons.

Male and female common loons look alike, though males are usually larger than the females. Young common loons look similar to winter adults, but have more white on their head and back. This juvenile plumage is maintained through their first summer. (McIntyre and Barr, 1997; "Field guide to the birds of North America, Second Edition", 1987; Peterson and Peterson, 2002; Robbins, et al., 2001)

  • Sexual Dimorphism
  • sexes alike
  • male larger
  • Range mass
    1600 to 8000 g
    56.39 to 281.94 oz
  • Range length
    70 to 90 cm
    27.56 to 35.43 in
  • Average wingspan
    152 cm
    59.84 in

Reproduction

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 signal 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 approximately two feet in diameter of soil, grasses, moss or vegetation. The nest is usually in a sheltered location near deep water, allowing the male and female to swim to and from the nest undetected by predators. Often nests are built on islands or peninsulas projecting into the water. When the nest is completed, 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 chicks hatch asynchronously, up to a day apart. They stay in the nest for a day or two after hatching, after which time they leave the nest with the parents and return to shore only rarely. The fledgling phase lasts 2 to 3 months, during which the young chicks accompany their parents around the territory, 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)

  • Breeding interval
    Common loons breed once yearly.
  • Breeding season
    Common loons breed in the spring, beginning soon after the ice covering the lakes breaks up.
  • Range eggs per season
    1 to 3
  • Average eggs per season
    2
    AnAge
  • Average time to hatching
    29 days
  • Average time to hatching
    28 days
    AnAge
  • Range fledging age
    1 to 2 days
  • Range time to independence
    2 to 3 months
  • Range age at sexual or reproductive maturity (female)
    2 to 3 years
  • Range age at sexual or reproductive maturity (male)
    2 to 3 years

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)

  • Parental Investment
  • precocial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • protecting
      • male
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • male
      • female
    • protecting
      • male
      • female

Lifespan/Longevity

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)

Behavior

During the breeding season, most loons are found in breeding pairs. However, small flocks of unmated individuals and unsuccessful breeders may also be seen during the breeding season. The breeding territory of loon pairs ranges from 0.24 to 0.81 square kilometers.

Common loons are migratory, leaving their breeding grounds beginning in September. They migrate by day, singly or in flocks of up to 15 individuals. During migration, loons may spend the nights in flocks of several hundred individuals on large inland lakes. On their wintering grounds, individuals defend small feeding territories of 0.04 to 0.08 square kilometers during the day, but flock together at night.

Common loons are specialized swimmers. Their legs are placed very far back on their bodies, making them very powerful underwater swimmers. However, this arrangement also makes walking difficult for these birds. ("", 2003; "", 2001; Stokes and Stokes, 1983)

  • Range territory size
    0.04 to .81 km^2

Communication and Perception

Common loons use visual displays and vocalizations to communicate. Stokes and Stokes (1983) identified six visual displays and five types of vocalizations used by common loons. These displays and vocalizations are used in courtship, territorial disputes, communication between pairs and offspring, and between flock members, and to signal alarm. (Stokes and Stokes, 1983)

Food Habits

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)

  • Animal Foods
  • fish
  • insects
  • terrestrial worms
  • aquatic crustaceans

Predation

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)

Ecosystem Roles

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.

Economic Importance for Humans: Positive

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.

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

Because common loons eat fish, they are viewed by some people as competition for fishermen.

Conservation Status

Common loons are threatened primarily by habitat loss and/or degradation. Loons are highly sensitive to human disturbance through recreation or development on formerly secluded lakes. They are also threatened by industrial pollutants, such as mercury and other heavy metals that accumulate in the loons' bodies and slowly poison them. Acid rain kills phytoplankton, collapsing the aquatic food chains that loons depend on for food.

Oil spills are deadly to loons, which are unable to fly, dive or swim when their plumage becomes saturated with oil. Lead poisoning from ingestion of lead sinkers and entanglement in fishing nets are other sources of mortality.

Common loons are not considered federally endangered or threatened. However, they do have special conservation status in some states, including Michigan, where they are listed as threatened. They are also protected by the U.S. Migratory Bird Act. ("", 2001)

Contributors

Kari Kirschbaum (author, editor), Animal Diversity Web.

Roberto J. Rodriguez (author), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

food

A substance that provides both nutrients and energy to a living thing.

freshwater

mainly lives in water that is not salty.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

migratory

makes seasonal movements between breeding and wintering grounds

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

piscivore

an animal that mainly eats fish

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

visual

uses sight to communicate

young precocial

young are relatively well-developed when born

References

National Geographic Society. 1987. Field guide to the birds of North America, Second Edition. Washington, DC: The National Geographic Society.

2003. C Perrins, ed. The New Encyclopedia of Birds. Oxford: Oxford Univeristy Press.

2001. C Elphick, J Dunning, D Sibley, eds. The Sibley Guide to Bird Life and Behavior. New York: Alfred A. Knopf.

2003. "USGS Upper Midwest Environmental Sciences Center" (On-line). Accessed October 06, 2004 at http://www.umesc.usgs.gov/terrestrial/migratory_birds/loons/questions.html.

IUCN, 2003. "2003 IUCN Red List of Threatened Species" (On-line). Accessed October 06, 2004 at http://www.redlist.org/.

McIntyre, J., J. Barr. 1997. Common Loon (Gavia immer). A Poole, F Gill, eds. The Birds of North America, Vol. 313. Philadelphia, PA and Washington DC: The Academy of Natural Sciences and the American Ornithologists Union.

Peterson, R., V. Peterson. 2002. A field guide to the birds of Eastern and Central North America. New York: Houghton Mifflin Company.

Robbins, C., B. Bruun, H. Zim. 2001. Birds of North America; A guide to field identification. New York: St. Martin's Press.

Stokes, D., L. Stokes. 1983. Stokes guide to bird behavior, Volume III. New York: Little, Brown and Company.

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