The Trumpeter Swan
 Swan pair with day-old cygnet |
Rocky Mountain Trumpeter Swan
Range Expansion Program
Pacific Flyway Council and U.S. Fish and Wildlife Service
Original text by Ruth Shea, The Trumpeter Swan Society.
Revisions by Linda Rawley, Wildlife Specialist, Utah Division of Wildlife Resources
History of Rocky Mountain Trumpeter Swans
Once abundant and widespread throughout much of North America, trumpeter swans were nearly extinct by 1900. Both their numbers and their distribution were severely reduced by subsistence hunting, the commercial plumage trade, and habitat changes. The only trumpeters that survived were those that lived year-round in remote areas or whose traditional migration patterns avoided areas of human settlement.
Small flocks persisted only in Alaska and remote habitats of the Rocky Mountains. In the lower 48 states and Canada, the last remaining trumpeters, numbered only about 200 by the 1930s and survived by wintering in the frigid wilderness of Greater Yellowstone where warm springs kept small areas of water ice-free regardless of winter severity. Although winter habitat was meager and limited by ice formation, the swans found crucial security from shooting .
This last remnant that wintered in Greater Yellowstone included about 80 swans that were year-round residents and about 100 that migrated south each fall from Canadian nesting areas near Grande Prairie, Alberta. Virtually all other trumpeters that once had migrated south to milder wintering areas had ben destroyed by 1930 and the use of those traditional migration routes was lost.
Although still among the least abundant of our native waterfow, decades of conservation efforts have helped the Rocky Mountain trumpeters increase to about 5,000 birds. Despite this promising growth in numbers, their winter distribution remains restricted primarily to the Tri-State, (or Greater Yellowstone) area of southwest Montana, western Wyoming, and eastern Idaho. Less than 75 pairs nest in the entire western U.S. south of Canada.
Historic migrations to winter habitats further south have not yet been restored. As a result, each fall the growing flocks of Rocky Mountain trumpeters from Canada and the much smaller group of Tri-State residents congregate in their primary wintering area, the rivers of Greater Yellowstone.
The Problem
In eastern Idaho, this lack of dispersal southward has created a severe "bottleneck" as increasing numbers of trumpeters arrive from Canadian nesting areas to spend the winter on the Snake R and its tributaries . At some sites, most notably Harriman State Park on the Henry’s Fork of the Snake River the aquatic plants can no longer provide enough winter food to support the increasing flocks of swans, Canada geese, and ducks.
By 2009, over 4000 swans were wintering in eastern Idaho, with the largest concentrations on the Henry's Fork, the Teton River, and the South Fork of the Snake River. Although much of this area has provided adequate habitat during recent mild winters, when a severe winter strikes this region, most of the rivers in this region will freeze. Mortality will likely be high among swans that attempt to remain at these sites and could impact all the known Canadian and Tri-state breeding flocks because all winter together in this region.
Despite the promising increase of Rocky Mountain trumpeters, until we restore their migrations and help them disperse to more suitable wintering areas, their recovery will remain questionable.
Why Haven’t the Swans Moved South?
In addition to the loss of historic migratory patterns, for almost 60 years the last remaining trumpeters were encouraged to winter in Greater Yellowstone. Although some attempted to explore and migrate further south, they had little success.
From 1935-1992, hundreds of trumpeters were fed grain during winter at Red Rock Lakes National Wildlife Refuge, 20 miles northwest of Harriman State Park. Large sanctuaries in Yellowstone and Grand Teton National Parks and at Harriman State Park also protected the swans from human disturbance. While artificial feeding and sanctuaries saved the population from extinction, they also discouraged the southward migration that is essential to long-term population recovery. Artificial feeding at Red Rock Lakes ceased in 1992.
Current Management Efforts
From 1988 to 2005, over 1,700 trumpeter swans were captured at Harriman State Park and Red Rock Lakes National Wildlife Refuge and transplanted to new habitats in southcentral Oregon, southern Idaho, and southwest Wyoming. Somel were also moved to Utah. The goal of translocations was to encourage exploration and future use of more diverse wintering sites and to broaden nesting distribution in the Intermountain West.
Transplanted swans were neck collared and dyed, and closely monitored through a network of observers.
The disturbance from trapping and occasional planned hazing disturbance has reduced the number of swans wintering in the vicinity of Harriman State Park. However, large wintering concentrations now occur at many sites in eastern Idaho that will freeze during a severe winter.
Transplanted swans have been sighted in all western states and are slowly increasing use of other wintering sites as far west as Oregon and California. Serious problems remain in eastern Idaho, however, as wintering swans continue to increase.
Up through 1995, biologists attempted to establish trumpeter swan migrations that would avoid tundra swan hunting areas. This was done to minimize the potential for a legal tundra swan hunter to accidentally harvest a trumpeter.
Beginning in 1994, tundra swan hunting regulations in Utah, Nevada, and Montana were changed to reduce the potential harvest of trumpeters, and to protect legal tundra swan hunters from prosecution should they accidentally harvest a trumpeter. These changes enabled biologists to transplant trumpeters into areas of Utah where they have a greater potential to follow migrating tundra swans to southern wintering areas where food resources are plentiful.
Unless the present "bottleneck" can be opened, increasing numbers of trumpeters from across western Canada will continue to end their southward migration in the Tri-State area. They must either be persuaded to migrate through this region and continue south or they will eventually exceed the carrying capacity of winter habitat and die there. The Tri-State’s resident nesting swans, forced to share marginal winter sites with the growing Canadian flocks, will also be at risk.
Management Options
Management options are limited. Substantial mortality is likely unavoidable; the problem has developed over decades and will not be easily solved. Additional transplants may help create use of other wintering areas but cannot possibly remove enough swans from eastern Idaho to reduce them to a level that could survive a harsh winter.
During the past decade, efforts have focused on expanding the nesting distribution of Tri-state trumpeters into lower elevation sites in Idaho, Wyoming and Montana. The goal is to broaden their nesting distribution, while simultaneously encouraging the resident swans to diversify their wintering sites. Artificial feeding can no longer meet the needs of the increasing flocks. Feeding would concentrate swans as well as ducks and geese, creating a high risk of disease and discouraging migration.
Systematic hazing of trumpeters out of the Harriman State Park area was also used in several years during the past decade. Managers also maniplated water flows in the Henrys Fork from Island Park Dam to benefit the fishery, while also discouraging winter swan use. By 2009 substantial numbers of swans had shifted southward in eastern Idaho and hazing was no longer necessary at Harriman State Park. Although no single concentration area is now of specific concern, near record number of swans are wintering throughout eastern Idaho.
Long-term population security will depend upon the survival of trumpeters in a wide variety of wintering sites. Currently, the Pacific Flyway Council is emphasizing continued expansion of nesting areas of Tri-state trumpeters and monitoring to better understand the migration corridors used by the Rocky Mountain trumpeter swans.
