Osprey

Like many other birds of prey, osprey (Pandion haliaetus) populations declined due to pesticide use in the mid-1900s and rebounded in the latter part of the century, after the banning of pesticides such as DDT. The first study of osprey in Yellowstone National Park occurred in 1917 by M. P. Skinner, the park’s first naturalist. It was not until 1987 that the Yellowstone National Park bird program began monitoring breeding osprey annually, although an extensive survey on reproduction, diet, and habitat was conducted during the 1970s.

Ospreys are surveyed via fixed-wing aircraft and by ground-based surveys from May through August. During the survey flights, the majority of nests are monitored for occupancy and breeding activity. In addition, all suitable lakes and rivers are surveyed for potential new territories and nest sites.

Since monitoring began, Yellowstone’s population of osprey has declined, particularly on and around Yellowstone Lake. Nest success has remained relatively stable, with about 50% of nests producing one to two young per year.

Number in Yellowstone

In 2022, 15 active nests were monitored, of which 67% were successful, above the 35-year average (54%).
Productivity for active nests in 2022 (1.3 young per nesting female) was also above the 35-year average (0.92).
No osprey were detected nesting on Yellowstone Lake in 2022.

Identification

Slightly smaller than the bald eagle.
Mostly white belly, white head with dark streak through eye.
Narrow wings, dark patch at bend.
Fledglings have light edges to each dark feather on their backs and upper wing surfaces, which gives them a speckled appearance.

Habitat

Dependent on fish for food, osprey are usually found near lakes (such as Yellowstone Lake), river valleys (such as Hayden, Madison, Firehole, and Lamar valleys), and in river canyons (such as the Gardner Canyon and the Grand Canyon of the Yellowstone River).

Behavior

Generally returns to Yellowstone in April and leaves in September.
Builds nest of sticks in large trees or on pinnacles close to water.
Lays 2–3 eggs in May to June.
Eggs hatch in 4–5 weeks.

Research

A recently completed study conducted by park biologists found a significant relationship between the declines in cutthroat trout and osprey reproduction at Yellowstone Lake. Recent increases in the number of young cutthroat trout caught by the Yellowstone fisheries program during the fall netting assessment are encouraging. An increase in cutthroat trout production may lead to an increase in nesting pairs of ospreys and improved nesting success at Yellowstone Lake.

Resources

Annual Bird Program Reports. National Park Service, Yellowstone National Park. https://www.nps.gov/yell/learn/nature/birdreports.htm

Baril, L.M., D.W. Smith, T. Drummer, and T.M. Koel. 2013. Implications of cutthroat trout declines for breeding ospreys and bald eagles at Yellowstone Lake. Journal of Raptor Research 47(3): 234–245.

Poole, A.F., R.O. Bierregaard, and M.S. Martell. Osprey. The Birds of North America Online. https://birdsna.org/Species-Account/bna/species/osprey/introduction