Trumpeter Swan

Trumpeter swans are a species of concern in Yellowstone.

NPS/Amanda Boyd

 

The trumpeter swan (Cygnus buccinator), named for its resonant call, is North America’s largest wild waterfowl, with a wingspan of up to eight feet. These swans require open water, feed mainly on aquatic plants, and nest in wetlands. Although they once nested from Alaska to northern Missouri, trumpeter swans were nearly extirpated in the lower 48 states by 1930 due to habitat loss and hunting. A small population survived in the Greater Yellowstone Ecosystem of approximately 70 birds. With intensive management, this population provided the basis for widespread swan recovery later in the century.

As a result of conservation measures, populations across the continental United States began increasing. As of 2015, there are approximately 63,000 trumpeter swans in North America belonging to three distinct subpopulations: the Pacific, the Rocky Mountain, and the Interior. Swan numbers in the Greater Yellowstone Ecosystem, belonging to the Rocky Mountain subpopulation, grew steadily through the early 1960s, after which cygnet production in Yellowstone and subsequent recruitment of adults into the breeding population began declining.

 

Number in Yellowstone

28 resident swans in 2022, including three territorial pairs. Trumpeter swans are increasing in the Rocky Mountains, stable in the Greater Yellowstone Ecosystem, but declining in Yellowstone National Park.

Identification

• White feathers, black bill with a pink streak at the base of the upper mandible.
• During migration, can be confused with the tundra swan. Trumpeters are larger, have narrower heads, have a pink mandible stripe, have no yellow spot in front of the eye.

Habitat

• Slow-moving rivers or quiet lakes.
• Nest is a large, floating mass of vegetation.

Behavior

• Feed on submerged vegetation and aquatic invertebrates.
• Low reproduction rates.
• Can fail to hatch eggs if disturbed by humans.
• Lay 4–6 eggs in June; young (cygnets) fledge in late September or early October.
• Usually in pairs with young in summer; larger groups in winter.

Management Concerns

• Limiting factors in Yellowstone appear to be flooding of nests, predation, possibly effects of drought caused by climate change, and less immigration into the park from outside locations.
• Because swans are sensitive to human disturbance during nesting, nest areas are closed to public entry.

 

Current nesting range of trumpeter swans.

Population

The park’s resident trumpeter swan population increased after counts began in 1931 and peaked at 72 in 1961. The number began declining shortly after and dropped further after the Red Rock Lakes National Wildlife Refuge feeding program ended and winter ponds were drained in the early 1990s. Other factors contributing to the decline may include predation, climate change, and human disturbance. In 2022, park biologists observed 28 trumpeter swans in Yellowstone, including 26 adults and 2 cygnets. Two pairs attempted to nest in the park, on Swan Lake and an unnamed pond in the Bechler region, and a third pair on Grebe Lake did not nest in 2022. Other apparent pairs were observed throughout the park but no other nesting was detected. Only Swan Lake was successful and fledged two cygnets.

Six young trumpeter swans were released in Yellowstone in 2022 in Hayden Valley on the Yellowstone River, near the confluence with Alum Creek. Staff hope that these released swans will become bonded to their release location and return the following spring. In total, the park has released 56 cygnets over a 10-year period. At least one of the swans at Swan Lake was released as a cygnet in YNP.

Swans typically take at least four years to reach sexual maturity, so biologists are hopeful more of these young birds may breed in coming years. The release program is part of an ongoing effort to augment Yellowstone’s swan populations and increase the number of breeding pairs that nest inside the park.

Nearly all Rocky Mountain trumpeter swans—including several thousand that migrate from Canada—winter in ice-free waters in the Greater Yellowstone Ecosystem, but only a portion of them remain here to breed.

The best available scientific evidence suggests that Yellowstone provides marginal conditions for nesting and acts as a sink for swans dispersing from more productive areas. This effect has been compounded in recent decades by reduced wetland areas (due to long-term drought or warmer temperatures) and community dynamics (e.g., changes in bald eagle diets due to the limited availability of cutthroat trout in Yellowstone Lake). Trumpeter swan presence in the park may therefore be primarily limited to occasional residents and wintering migrants from outside the park. Concern about the Greater Yellowstone Ecosystem population has resulted in cooperative efforts between state and federal agencies to monitor swan distribution and productivity.

Across the region, federal agencies currently survey swans in September to estimate the resident swan population and annual number of young cygnets produced.

 

Outlook

Trumpeter swans are particularly sensitive to human disturbance. Because of this, park managers restrict human activity in known swan territories and nesting areas. Scientists are also conducting studies to better determine the habitat requirements for nesting swans and the drivers for the observed local population decline.

 

 

Resources

Mitchell, C.D., and M.W. Eichholz. Trumpeter swan. The Birds of North America Online. http://bna.birds.cornell. edu/bna/

Proffitt, K.M. 2008. Yellowstone National Park trumpeter swan conservation assessment. Rocky Mountains Cooperative Ecosystem Studies Unit.

Proffitt, K.M., T.P. McEneaney, P.J. White, and R.A. Garrott. 2009. Trumpeter swan abundance and growth rates in Yellowstone National Park. Journal of Wildlife Management 73:728–736.

Proffitt, K.M., T.P. McEneaney, P.J. White, and R.A. Garrott. 2010. Productivity and fledging success of trumpeter swans in Yellowstone National Park, 1987–2007. Waterbirds 33:341–348.

Smith, D.W. and N. Chambers. 2011. The future of trum- peter swans in Yellowstone National Park: Final report summarizing expert workshop, April 26–27, 2011. National Park Service, Yellowstone Center for Resources, Yellowstone National Park, Wyoming.

Squires, J.R. and S.H. Anderson. 1995. Trumpeter swan (Cygnus buccinator) food habits in the Greater Yellowstone Ecosystem. American Midland Naturalist 133(2):274–282.

Squires, J.R. and S.H. Anderson. 1997. Changes in trum- peter swan (Cygnus buccinator) activities from winter to spring in the greater Yellowstone area. American Midland Naturalist 138(1):208–214.

White, P.J., K.M. Proffitt, T.P. McEneaney, R.A. Garrott, and D.W. Smith. 2011. Yellowstone’s trumpeter swans in peril? Drastic decrease in resident swans over the past 40 years. Yellowstone Science 19:12–16.