Common Loon

A lone loon swimming on a lake near a rock cliff.
The common loon is a species of concern in Yellowstone.



The park’s common loon (Gavia immer) population is one of the most southerly breeding populations in North America. The majority of Wyoming’s population of breeding common loons occurs in Yellowstone. The common loon is listed as a Species of Special Concern in Wyoming because of its limited range, small population, sensitivity to human disturbance, and loss of breeding habitat outside of Yellowstone. Wyoming’s breeding loon population is isolated from populations to the north by more than 200 miles, limiting immigration from other populations. Since the mid-2000s, Wyoming’s population has declined by 42%. Yellowstone’s loon population has declined since surveys began in 1989. However, detailed data from a study initiated in 2012 indicate that the number of loons present in the park can vary widely from year to year. Continuing research will try to analyze any trends in productivity, nesting success, and number of breeding pairs to attempt to determine why some years are more productive than others.


Number in Yellowstone

  • In 2016, 31 loons in 14 lakes. 13 territorial pairs in 12 lakes.
  • In 2015, 26 loons in 13 lakes. 11 territorial pairs.


  • Breeding adults (March–October) have black and white checkering on back, a black bill, red eyes, and iridescent green head and neck. The neck has a black and white chinstrap and distinctive collar.
  • Loon chicks hatch with a blackish- brown down and white belly and retain this plumage for two weeks. Body feathers emerge at 41⁄2 weeks on the chick’s upper back. By six weeks, brown down only remains on the neck and flanks.
  • Gray juvenile plumage is present at seven weeks.
  • Juveniles and winter adults have dark upperparts and white underparts.


  • Summer on ponds or lakes: large lakes, such as Yellowstone, Lewis, and Heart Lakes; and smaller ones such as Grebe and Riddle Lakes.
  • Winter on open water.
  • May be found foraging or resting on larger, slow moving rivers.
  • Nest sites are usually on islands, hummocks in wetlands, or floating bog mats.
  • Pairs nesting on lakes smaller than 60 acres usually require more than one lake in their territory. Lakes smaller than 15 acres are rarely used.


  • Primarily eat fish (4–8 inches).
  • Unable to walk on land.
  • Migrate in loose groups or on own, not in organized flocks. Arrive at summer lakes and ponds at or soon after ice-off.
  • Four common calls: wail—for long distance communication, yodel—used as a territorial signal by males only, tremolo—a staccato call, usually by an agitated adult, and hoot—a contact call, often between adults or adults and their young.
  • Females generally lay two eggs, typically in June.
  • Males and females share incubation duties equally. Chicks hatch after 27–30 days. Both adults also care for their young.
  • Chicks are able to fend for themselves and attain flight at 11–12 weeks.
  • In late summer, adults form social groups, especially on larger lakes, before leaving in October.

Management Concerns

  • The breeding population in Wyoming is isolated; populations to the north are more than 200 miles away.
  • Loons can be bioindicators of the aquatic integrity of lakes, responding to lead and mercury levels.
  • All factors affecting loon reproduction in Yellowstone are unknown, but human disturbance of shoreline nests has a negative impact.


In 2016, park biologists checked at least 18 lakes for loon activity. Yellowstone Lake had two loon territories. Fourteen of the lakes were occupied by at least one loon, with a total estimate of 31 adult loons. Nine loonlets fledged during 2016.

A lone loon swimming across a lake.
Common loon spotted in Yellowstone.

NPS/Neal Herbert


In the western United States, common loons breed in Idaho, Montana, Washington, and Wyoming. The total western US breeding population is estimated at 90 territorial pairs. Wyoming’s breeding population is isolated and totals approximately 16 territorial pairs including 11 in Yellowstone. Western populations of breeding common loons are known to overwinter from Washington south to California. Spring and fall migrants in Wyoming represent breeding populations from Saskatchewan that overwinter around Mexico’s Baja California peninsula.



There are several threats to Wyoming’s loon populations. Direct human disturbance to shoreline nests and chicks lowers survival rates, as do the loss of breeding habitats and water level fluctuations (e.g., erratic spring flooding). Contaminants like lead (from sinkers) and mercury, in combination with hazards on wintering grounds (e.g., marine oil spills and fishing nets) challenge loon reproduction and survival even further.

Fish are the primary prey of loons. As part of a multi-park study on mercury concentration in fish, fish from various lakes where loons nest were screened for mercury. Fish were sampled from Beula, Grebe, Yellowstone, and Lewis Lakes. Fish from Beula, Grebe, and Yellowstone lakes exceeded the threshold at which fish-eating birds may be affected by mercury toxicity. Fish from Lewis did not exceed that threshold although they still contained mercury.

Loons are long-lived; they have relatively low chick production and a poor ability to colonize new breeding areas. Given the very small size and isolation of Wyoming’s breeding loon population, it is at a particularly high risk of local extinction.

Bald eagle standing over a fish that it's eating.

Bald Eagle

Bald eagles can be seen along Yellowstone's many rivers and lakes.

An osprey comes in for a landing on a nest, where its mate tends the nest.


Osprey summer in Yellowstone, fishing and raising young.

A peregrine falcon perched on a branch.

Peregrine Falcon

Peregrine falcons are some of the fastest birds.

A pair of white pelicans floating on water.

Colonial Nesting Birds

Colonial nesting birds—pelicans, gulls, and cormorants—primarily nest on the Molly Islands.

A pair of swans swimming on a lake.

Trumpeter Swan

Trumpeter swans are the largest wild waterfowl in North America.

A white-breasted bird with gray and black wings and black beak on a mound of snow

Songbirds and Woodpeckers

Passerine and near passerine species comprise the majority of bird species in Yellowstone.

A small, gray bird perched on a rock along a stream holding an insect in its beak.

American Dipper

Also known as the water ouzel, these birds dive into water for aquatic insects.

Profile of a raven's head and chest


Ravens are smart birds, able to put together cause and effect.

A sandhill crane walking through a marshy landscape.

Sandhill Crane

Sandhill cranes nest in Yellowstone during the summer.

A yellow-breasted bird with black markings calls out as it stands on a stick


About 150 species build their nests and fledge their young in Yellowstone.

An eared grebe near Mammoth Hot Springs

Sound Library

Immerse yourself in the aural splendor of Yellowstone.



Annual Bird Program Reports. National Park Service, Yellowstone National Park.

Mcintyre, Judith W., Jack F. Barr, David C. Evers, and James D. Paruk. Common loon. The birds of North America Online.

Last updated: July 17, 2018

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Mailing Address:

PO Box 168
Yellowstone National Park, WY 82190-0168



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