Colony Nesting Birds

Many large white birds compose a flock on the shore of an island.
American white pelicans—and other colonial nesting birds—nest primarily in the southeast arm of Yellowstone Lake.



Colonial nesting birds nest primarily on the Molly Islands in the southeast arm of Yellowstone Lake. These two small islands are cumulatively just 0.7–1.2 acres in size, depending on lake water levels, yet hundreds of birds have nested there in a single year.

Prior to the late 1970s, the Molly Islands were surveyed only intermittently. Some data goes back to 1890 when nesting American white pelicans (Pelecanus erythrorhynchos) and California gulls (Larus californicus) were first noted in this area. Caspian terns (Hydroprogne caspia) are suspected of nesting on the Molly Islands as early as 1917, although information on breeding status was not collected until 1933. Double-crested cormorant (Phalacrocorax auritus) nests were confirmed by 1928.

Currently, pelicans, California gulls, and doublecrested cormorants nest with varying rates of success. Photographic interpretation from three aerial surveys conducted June through August 2021, showed approximately 577 pelican nests that fledged an estimated 341 young. Biologists were unable to confirm if 10 nesting double-crested cormorants were successful in fledging any young. Two California gulls nested but successful fledging could not be determined. As in recent years, no Caspian terns were observed on the islands.



Birds nesting on the Molly Islands are subject to extreme environmental conditions ranging from flooding, frosts that can occur at any time of year, and high winds. As a result, birds nesting there experience large year-to-year fluctuations in the number of nests initiated and fledglings produced. Populations of American white pelicans, California gulls, and double-crested cormorants have declined over the last 20 years. Caspian terns (Hydroprogne caspia) have not nested on the islands since 2005.

The reasons for the decline in colonial nesting birds are not well understood, but a previous study indicates that high levels of water in Yellowstone Lake are associated with low reproduction for nesting pelicans. Notably, quick spring melt-off events can cause a significant rise in the water level on Yellowstone Lake and flood the Molly Islands.

The decline in cutthroat trout, a known food source for the Molly Island colonial nesting birds, may also influence nesting success. Furthermore, bald eagles on Yellowstone Lake that formerly depended on cutthroat trout may have switched prey to target the flightless and vulnerable young of these colonial nesting species.



Evans, R.M., and F.L. Knopf. American white pelican. The Birds of North America Online.

Varley, J. D., and P. Schullery. 1995. The Yellowstone Lake crisis: confronting a lake trout invasion. Yellowstone National Park, Wyo: Yellowstone Center for Resources, National Park Service.

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 loon swimming on a lake.
Common Loon

Loons in Yellowstone are some of the southern most breeding populations.

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 group of rust-brown-headed birds fly over a body of water.

Spring is a wonderful time to look for birds, as migration brings many birds back to the park.

A young bison calf with rust-red fur.

Learn about the park's abundant and diverse species—67 mammals, 330 birds, 16 fish, 5 amphibians, and 6 reptiles.


Last updated: May 2, 2023

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Yellowstone National Park, WY 82190-0168



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