Rocky Mountain: Trumpeter Swan Migration Project

Background

By 1900, Trumpeter Swans were near extinction across North America due to overharvest and habitat alteration. As the populations declined, their migrations to traditional wintering areas were almost totally destroyed. By the 1940s, only about 100 trumpeters survived in western Canada, breeding on the lakes near Grande Prairie, Alberta. In fall, most of this remnant apparently migrated to the Greater Yellowstone region, where they wintered side-by-side with the Greater Yellowstone breeding population, the only nesting group in the lower 48 states to escape extinction. Here, in this high elevation remote region, these two last groups wintered in relative safety from the shooting that had eliminated swans that attempted to migrate further south to more inhabited regions. Although winter weather in Greater Yellowtone was harsh, hot springs kept some streams ice-free during even the most severe periods, and the last wintering Trumpeter Swans in the lower 48 states persisted in this high mountain refuge.

Despite decades of conservation efforts, the Greater Yellowstone breeding population remains extremely limited in numbers and distribution, with slightly less than 300 adults restricted to nesting areas in southwest Montana, western Wyoming, and eastern Idaho. In contrast, in recent decades the Western Canada population has begun to reoccupy vacant breeding habitat in Alberta, British Columbia, the Yukon, and the Northwest Territories and now numbers about 4,700 swans.

During the past decade of unusually mild winters, increasing numbers of Canadian Trumpeters have been able to winter in Greater Yellowtone, feeding on aquatic vegetation in waters that will freeze during a severe winter. Concern is great that unless historic migrations southward from this region are re-established, a severe winter in Greater Yellowstone could lead to the starvation of large numbers of swans. Such mortality could set back the restoration of Trumpeter Swans in western Canada, and jeopardize the continued existence of the Greater Yellowstone population.

The goal of the Trumpeter Swan Migration Project was to mark Trumpeter Swans at their nesting areas in western Canada, using satellite-tracked radios and neckbands to determine their migration routes and wintering areas.

The purpose of this research was to answer three fundamental management questions:

  1. Are Western Canadian Trumpeter Swans successfully rebuilding migrations to diverse wintering areas that could be used in restoration programs to improve their security?
  2. What is the extent of the breeding range of the swans that are wintering in Greater Yellowstone where the risk of winter mortality is high?
  3. What migration routes and key spring and fall stopover sites are the swans using?

Marking the Swans

During July 2002 and 2003, TTSS launched the first attempt to radio-track Trumpeter Swans from the Western Canadian Population. Led by Dr. Rod Drewien of the Hornocker Wildlife Institute and assisted by biologists from the U.S. Fish and Wildlife Service, Canadian Wildlife Service, and Ducks Unlimited, Canada, we used a float plane to capture 43 flightless swans during the mid-summer molt on their breeding areas in the Yukon and northern British Columbia. We placed satellite-tracked radio transmitters on 13 adult Trumpeter Swans and put individually coded neck bands on an additional 30 adults to increase sample size. Swans were members of territorial pairs and most had cygnets. Capture locations were distributed as widely as possible to increase the chances of detecting diverse migratory patterns.

Key findings

  1. The migration corridor currently used by the Western Canada Population in spring and fall follows a narrow band along the eastern front of the Rocky Mountains (Figure 1). Although swans use a variety of wetlands as stop over foraging sites, most lie within a band that is often less than 50 miles wide. Most migrating Trumpeters spend a month or more foraging along the migration route and almost all stopped over in the Grande Prairie region in spring and fall.
  2. Radio data and neckband resightings provided no evidence that any swans from the Western Canada population have successfully rebuilt severed migration patterns to wintering sites outside of the Greater Yellowstone region. It is appears that virtually the entire Western Canadian population, as well as the Greater Yellowstone population, could be impacted when a severe winter strikes the region and freezes the major foraging areas.
  3. Swans from nesting areas thoughout the eastern and central Yukon, east of Highway 2 from Whitehorse to Dawson, are virtually all funneling in to the Greater Yellowstone wintering area. Swans nesting west of Whitehorse appear to be affiliated with the Pacific Coast Population and migrate to wintering areas in southern British Columbia and northwest Washington (Fig. 2).
  4. Protection of wetlands in the narrow migration corridor along the East Front of the Rockies in southwestern Alberta and central Montana will be essential to ensure that the quality of migration stopover sites is maintained in the future. Nutrition gained at these sites will likely be quite important for both the winter survival and nesting productivity of the population. The Western Canada Population will remain vulnerable to high winter mortality, however, until migrations to more diverse wintering sites are rebuilt. Continued management effort is needed to encourage use of wintering sites south of Greater Yellowstone and to protect Trumpeters that attempt to migrate to other areas.

Our Partners

This research was made possible through contributions provided by the Yellowstone to Yukon - Wilburforce Foundation Science Grants Program, the U.S. Fish and Wildlife Service, the Canadian Wildlife Service, Dr. Arnie Fredrickson, and Ducks Unlimited, Canada.