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Gavia arcticaarctic loon(Also: black-throated diver;arctic loon)

By Tewodros Desta

Geographic Range

Arctic Loons or black-throated divers (Gavia arctica) have a large global distribution, as they are found across roughly 10 million square kilometers. They are a migratory species, restricted to regions throughout the northern hemisphere.

The winter range of Arctic loons is much more extensive than that of their breeding range. In winter, they are primarily found on large lakes off the coasts of Europe, Asia and North America, including the northern tundra and taiga habitats of Canada, Russia, Scandinavia and Greenland. European populations typically inhabit areas ranging from the Baltic Sea to the northern Mediterranean during winter months. North American populations commonly settle along the Pacific coast from the Gulf of Alaska to Baja California during the winter. Throughout the breeding season, Arctic loons extend across portions of Eurasia, and occasionally extend to parts of western Alaska. Roughly half of the western European population breeds in Sweden. Vagrant or accidental individuals also have been noted in northern Africa, southwestern Europe, western Middle East, and India. (BirdLife International, 2009; Conant, et al., 1996)

Habitat

Arctic loons breed on deep, productive, freshwater lakes or extensive pools with neighboring islands, peninsulas and other humanly-inaccessible nesting sites. They prefer a habitat free of disturbance. Gavia arctica relies on its freshwater breeding territory to provide food. They dive deep in the water for fish and also feed their offspring small fishes and insects until they increase in size, enabling them to feed on larger fish. Outside of the breeding season the species is commonly located among inshore waters along sheltered coasts. Gavia arctica is also occasionally found throughout large inland bodies of freshwater such as natural lakes or streams, and large rivers. (Jackson, 2003)

Arctic loons build their nest in May and June, and take about a week to complete. A nest contains piles of aquatic vegetation close to the edge of the water body, usually near a sheltered bay, island, or adjacent river system. (Petersen, 1979)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • coastal

Physical Description

Arctic loons grow to an average of 40 to 81 cm in body length. These birds have wing lengths ranging between 114 and 124 cm and have a mean body weight fluctuating between 2 and 3.4 kg. In breeding plumage, they feature white-spotted, black backs segmented into white lines, which are visible above the water while swimming. The head and posterior half of the neck are gray. The front half of the neck has a bold black stripe with long, thin vertical white stripes along both sides of the throat. Commonly referred to as “black-throated loons” which was coined by the black stripe on the throat. During the non-breeding season, the crown and nape darken to black, as does the back which loses the white barring. The face, throat and breast become starkly white and unmarked. This species closely resembles Pacific loons (Gavia pacifica) but may be distinguished by an extensive white flank patch that is present in both breeding and winter plumages. Female and male Arctic loons are similar in their physical appearances and feature distinctive, deep-red eyes. Juveniles closely resemble wintering adults, but are a more dusky-gray versus black and may exhibit a faint scaled pattern on their backs and wings. (Sjolander, 1978)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    2 to 3.4 kg
    4.41 to 7.49 lb
  • Range length
    40 to 81 cm
    15.75 to 31.89 in
  • Range wingspan
    114 to 124 cm
    44.88 to 48.82 in

Reproduction

Arctic loons are monogamous, meaning they live their whole lives with only one mate. The couple stays together during their winter migration and on their wintering grounds. New couples use a number of synchronous movements including bill-dipping, splash diving and rushing under water. Mating occurs on the water banks and often occurs right after the birds have arrived in the breeding area. This species exhibits strong site fidelity and often uses the same nesting site for every breeding season. Gavia arctica will continue to use this site for a short time following mating. (Petersen, 1979; Sjolander and Agren, 1972)

Arctic loons occupying southern regions begin their breeding season in May, whereas the breeding season in northern regions is determined by the onset of spring. In the spring they migrate from their wintering grounds. Upon nest completion the female will lay 1 to 3 eggs. The eggs are normally olive-brown with dark brown spots. Incubation takes 27 to 29 days followed by a vital growth period of 9 to 10 weeks. When the young are about two months old, they gain the ability to fly or "fledge". They reach sexual maturity in 2 to 3 years. (Sjolander, 1978)

  • Breeding interval
    Arctic loons breed once a year
  • Breeding season
    The breeding season varies geographically but occurs in spring
  • Range eggs per season
    2 to 3
  • Range time to hatching
    27 to 29 days
  • Average fledging age
    2 months
  • 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

The male loon is responsible for building the nest. Both parents take part in the incubation, but the females display a higher percentage of parental care. Incubation takes about 27 to 29 days followed by a vital growth period of 9 to 10 weeks, where both parents aid in rearing the offspring. The semiprecocial young spend the first day in the nest, but are able to swim at 2 to 4 days old. Both parents participate in feeding the young constantly throughout the first few weeks. Parents individually feed offspring one at a time, offering only one piece of food at a time, consisting usually of crustaceans. Newly hatched young often ride on their parents' backs, likely to avoid predators and conserve energy. At several weeks of age, the young start feeding themselves, but are still sometimes fed by their parents. When they are about two months old, they can fly and are considered fledgelings. They reach sexual maturity in 2 to 3 years. (Sjolander, 1978)

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

Lifespan/Longevity

Arctic loons are thought to be relatively long-lived birds. However, there is little information available directly pertaining to their lifespan. The oldest recorded wild Arctic loon lived to be 28 years old. (Elliott, 1992; Russell, 2010)

  • Range lifespan
    Status: wild
    28 (high) years

Behavior

Arctic loons fly and swim very well, but they are clumsy when walking on land since their legs are positioned far to the posterior end of their bodies. These birds cannot take flight from land and in calm conditions require 30 to 50 m of open water in which to take off safely without wind assistance. Normal takeoff involves springing into the wind, pattering for a considerable distance over the surface of the water and launching into the air. If necessary, Arctic loons will fly over 10 km in order to find food. To fish, their average dive lasts up to 45 seconds and reaches depths of up to 3 to 6 meters. These birds are able to use their wings as aids in underwater swimming. They dive head first and glide into the water without any difficulty. During migration they tend to gather in small travel groups. They are primarily a diurnal species that performs most activities during the day. (Jackson, 2003; Russell, 2010; Sven, 1977)

Home Range

Gavia arctica is a highly territorial species while on the breeding grounds, however exact territory size is unknown. It aggressively defends territory against any intruders. Arctic loons will display threatening postures to warn intruders to stay away. Fighting is common in both sexes, and males may fight to the death. Arctic loons use their bills and wings as weapons for defense. (Jackson, 2003)

Communication and Perception

Arctic loons produce a variety of calls. A low call, which is very weak and sounds much like a human humming, is performed by both female and male. Moaning occurs as a low call with a strong sound, produced by both sexes as early as two months of age. Yodeling, a "kuik-kukuik-kukuik” sound, is the strongest vocalization produced by the species, which is performed only by the male. Even in unfavorable conditions this call can be heard up to distances surpassing 10 km. Both low calls and moaning vocalizations are recognized as contact calls. The difference being, a low call is a normal contact call, moaning is a high intensity contact call. Yodeling is a territorial call made by the male loon preparing to defend his territory. Territorial calls are often paired with threatening behaviors such as circling or bill dipping to warn of an imminent attack.

Like most birds, Arctic loons perceive their environments through visual, auditory, tactile and chemical stimuli. (Arlott, 2009; Sjolander and Agren, 1972)

Food Habits

Gavia arctica are carnivores. They are primarily piscivorous, as their diet relies heavily upon fish, but also crustaceans and aquatic insects. They dive deep from the surface to feed. When a fish or other type of prey is caught, the loon throws back its head and swallows it. Newly hatched young are fed by their parents. Their diets consist predominantly of aquatic insects, with an increasing proportion of fish in their diet as they grow larger. In lakes with low densities of fish, young often are fed almost entirely on aquatic insects. (Mats, 1986)

  • Animal Foods
  • fish
  • insects
  • aquatic crustaceans

Predation

Arctic loon adults do not have many natural predators. Bald eagles are their main predators. Bald eagles attack unsuspecting, incubating parents. Young chicks also are vulnerable to predation by large predatory fish, bald eagles and herring gulls.

There are a number of other animals who primarily prey on eggs. Common egg predators include raccoons, gulls, crows and foxes. Predation on eggs of arctic loons takes place when an incubating adult is forced off the nest because of human disturbance, or if it is preoccupied by an intruder. During this time the unattended eggs quickly attract nearby predators. (Mudge and Talbot, 1993)

Adult Arctic loons respond to the sight of a predator with wailing and alarming vocalizations to inform both offspring and mates of the intruder. The young chicks respond by quickly swimming to a protected area of shoreline and remain hidden until the threat is no longer present. On freshwater lakes, adults are generally safe from underwater predators, but young chicks are vulnerable to large predatory fish. If an adult spots an underwater predator they will tread water rapidly with their feet and flap wings to discourage them from advancing any closer. (Mudge and Talbot, 1993)

Ecosystem Roles

Arctic loons serve as both prey and predator within their ecosystems. They provide food for local predators as well as control populations of fish, crustaceans and aquatic insects. They are also a host to several different body parasites, most of which are tapeworms and flukes. (Daoust, et al., 1998)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

Inuit, a member of the Eskimo peoples inhabiting northernmost North America from northern Alaska to eastern Canada, use Arctic loons' eggs for food. They sometimes hunt loons on the breeding ground for consumption as well. (Russell, 2010)

Economic Importance for Humans: Negative

Arctic loons feed primarily on fish and may be considered competitors for fishermen. (Russell, 2010)

Conservation Status

Arctic loons are vulnerable to human disturbances within their breeding sites. Changes in the habitat, including alterations of water levels, acidification of water as well as oil and heavy metal pollution are constant threats for this species. Current populations tend to be fairly large but are progressively decline throughout the southern part of their range. According to the assessment of the International Union for Conservation of Nature and Natural Resources (IUCN), Arctic loons are categorized as a species of least concern. The European breeding population of Arctic loons is relatively small (less than 92,000 pairs), and underwent a large decline between 1970 and 1990. On the other hand, Arctic loon populations in Sweden and Finland were stable and increased between 1990 and 2000. (BirdLife International, 2009; Petersen, 1979)

Contributors

Tewodros Desta (author), Radford University, Christine Small (editor), Radford University, Rachelle Sterling (editor), Special Projects.

Glossary

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.

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.

female parental care

parental care is carried out by females

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).

male parental care

parental care is carried out by males

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

polar

the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

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

social

associates with others of its species; forms social groups.

solitary

lives alone

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

tundra

A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short.

visual

uses sight to communicate

young precocial

young are relatively well-developed when born

References

Arlott, N. 2009. Birds of Europe, Russia, China, and Japan. Princeton, New Jersey: Princeton University Press.

BirdLife International, 2009. "Gavia arctica" (On-line). The IUCN Red List of Threatened Species. Accessed December 02, 2010 at www.iucnredlist.org.

Conant, B., R. King, J. Hodges, J. King. 1996. Status and trends of loon populations summering in Alaska 1971-1993. The Condor, 98/2: 189-195.

Daoust, P., G. Conoby, S. McBurney, N. Burgess. 1998. Interactive mortality factors In common loons from maritime Canada. Journal of Wildlife Disease, 34(3): 524-531.

Elliott, A. 1992. Handbook of Birds of the World. Volume 1: Ostrich to Ducks. Barcelona: Lynx Edicions.

Jackson, D. 2003. Between-lake differences in the diet and provisioning behavior of black-throated divers (Gavia arctica) breeding in Scotland. British Ornithologist Union, 145/1: 30-44.

Mats, E. 1986. Reproduction of the black-throated diver Gavia arctica in relation to fish density in oligotrophic lakes in southwestern Sweden. Holarctic Ecology, 9: 277-284.

Mudge, G., T. Talbot. 1993. The breeding biology and causes of nest failure of Scottish Black-throated Divers Gavia arctica. IBIS, 135/2: 113-120.

Petersen, M. 1979. Nesting Ecology of Arctic Loons. The Wilson Bulletin, 91/4: 608-617.

Russell, R. 2010. "Arctic Loon" (On-line). The Birds of North America Online. Accessed November 14, 2010 at http://bna.birds.cornell.edu/bna/species/657b/articles/conservation.

Sjolander, S. 1978. Reproductive Behavior of the Black-Throated Diver Gavia arctica. Ornis Scandinavica, 9/1: 51-65.

Sjolander, S., G. Agren. 1972. Reproductive Behavior of the Common Loon. The wilson Bulletin, 84/3: 296-308.

Sven, N. 1977. Adult Survival rate of the Black-throated Diver Gavia arctica. Ornis Scandinavica, 8: 193-195.

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