Effects of winter recreation on trumpeter swans

Authors(s): T. Oliff

Publication: Effects of winter recreation on wildlife of the Greater Yellowstone Area: a literature review and assessment. Report to the Greater Yellowstone Coordinating Committee. Yellowstone National Park, Wyoming.

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Publication Date: 0000-00-00

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Abstract: POPULATION STATUS AND TREND The trumpeter swan (Cygnus buccinator) is a species of special concern in Idaho (Category A) and Montana, and a Priority 1 species in Wyoming. In March 1989, the Idaho Chapter of the Wildlife Society petitioned the U.S. Fish and Wildlife Service to add the Greater Yellowstone Area (GYA) trumpeter swan population to the threatened species list, but the population was not listed. Concern over the dramatic decline in the GYA trumpeter swan population led to the establishment of the Greater Yellowstone Trumpeter Swan Working Group in 1997. During the 1800s and early 1900s, commercial trade in swan skins and habitat destruction reduced trumpeter swan populations to a fraction of historic levels. The species neared extinction in the lower 48 states, and isolated areas of protected habitat were critical to the survival of wild trumpeter swans (Banko 1960). The discovery of swans in the Centennial Valley in the 1930s led to the eventual establishment of Red Rocks Lakes National Wildlife Refuge. Management efforts at the refuge, as well as in a few other areas, have helped maintain trumpeter swan numbers in recent decades (Banko 1960, USFWS 1996). The GYA trumpeter swan population has fluctuated dramatically and declined in recent years to the levels of the 1940s. Areas inside and outside Yellowstone National Park provide habitat for both resident and migratory swans. One theory for the decline is that traditional migration patterns and knowledge of important winter and spring habitats were lost as the species neared extinction. Another theory is that the swan population never migrated out of the GYA in large numbers. As a result, virtually all of the breeding trumpeter swans of Canada and the Greater Yellowstone Area share the same high-elevation winter habitat in the GYA (T. McEneaney, Yellowstone National Park, personal communication). More than 10,000 swans currently exist in the wild. The Pacific population, representing most of the wild swans, breeds in Alaska and winters along the Pacific Coast from Alaska south to Washington (Ehrlich et al. 1988, Gale 1989). The mid-continental population of approximately 300 birds winters in the GYA. About 55 percent of these birds are year-round residents; the remainder migrate north and spend the summer in Canada (Gale 1989). Currently, the swan population in the GYA has exhibited declining productivity. In Yellowstone National Park, no cygnets were produced in 1996 or 1997. In 1995, two of eight nest attempts were successful in the park, and six cygnets were produced, but only two fledged. In 1994, five cygnets fledged (NPS 1996; T. McEneaney, Yellowstone National Park, personal communication). Winter habitat in the GYA is shared by resident and non-resident swans. Winter is a critical time for swans in the GYA as they are are vulnerable to reduced flows of water, heavy ice formation, unusually severe winter weather, disease, and environmental pollution. During the winter of 1988?89, about 100 swans died on the Henrys Fork as a result of ice formation on the river, which was due to low water flow and unusually low temperatures (Gale 1989; T. McEneaney, Yellowstone National Park, personal communication). LIFE HISTORY Trumpeter swans begin breeding between 3 and 6 years of age (most commonly at 4 or 5 years). They return to their breeding territories between February and late May. Most pairs remain together year-round and bond for life. The female normally lays between 4?6 eggs and incubates them for 33?37 days. The young hatch around late June and are precocial (they are mobile, downy, follow parents, and find their own food). The time from hatching to fledging ranges from 91?119 days. Cygnets remain with their parents through their first winter (Ehrlich et al. 1989, Gale 1989). Trumpeter swan winter habitat is associated with open water, especially along the Henrys Fork River and the thermally influenced waters of Yellowstone National Park. Winter habitat must provide extensive areas of ice-free open water where aquatic plants are available (Gale 1989, USFWS 1996, Banko 1960). NESTING HABITAT Breeding habitat is usually freshwater, especially the emergent vegetation on the margin of ponds, marshes, and lakes; however, brackish waters and slow-moving oxbows may be used. Nests are surrounded by water and built of aquatic and emergent vegetation, down, and feathers. Nests are often built on muskrat houses, beaver lodges, or small islands. Trumpeters generally use the same nest site for several years (Banko 1960). Breeding territory in the GYA ranges from 25?37 acres and generally coincides with the size of the nesting lake. At Red Rocks Lakes National Wildlife Refuge in Montana, breeding territories average 32 acres. Breeding pairs exclude other trumpeter swans from their territories during the nesting and brooding period (USFWS 1996, Reel et al. 1989). HUMAN ACTIVITIES Swan tolerance for people varies by season and situation. Swans seem to be more tolerant of humans during the winter months, but display reduced tolerance as spring approaches, and they are preparing to migrate or breed (T. McEneaney, Yellowstone National Park, personal communication; Shea 1979). Observations by Shea (1979) indicated that swans on the Madison River showed more tolerance to winter recreationists than did swans on the Yellowstone River. Swans wintered on the Madison River within 55 yards of the road, which had heavy snowmobile traffic. Swans often retreated when visitors stopped, but continued to feed. Swans on the Yellowstone River generally reacted to recreationists by swimming farther out from shore (Shea 1979). Swans at Harriman State Park in Idaho had a more pronounced reaction to human disturbance; when approached by a person on skis or snowmobile, swans broke into flight, often moving several miles to another stretch of the river (Shea 1979). POTENTIAL EFFECTS Swan conservation efforts in the GYA focus on ensuring adequate stream flows and protecting and enhancing nesting and wintering habitat. Nesting and brood-rearing seasons are critical times for swan survival and production. Disturbance by humans can have negative effects on trumpeter swans and other waterfowl. Henson and Grant (1991) note that: . . . disturbance can affect productivity in a number of ways including nest abandonment, egg mortality due to exposure, increased predation of eggs and hatchlings, depressed feeding rates on wintering and staging grounds, and avoidance of otherwise suitable habitat. In winter, problems occasionally arise when recreationists approach swans too closely. This kind of activity can lead swans to become habituated to humans, which may make them more prone to predation or roadkill. It can also lead to flushing swans from open water, resulting in increased energy requirements and a loss of energy reserves essential to surviving the winter and hatching and rearing young. The effect is exacerbated by the number of times a swan experiences disturbances. Aune (1981) found that swans appeared to become habituated to moving snowmobiles, but that they fly or swim away upon approach by foot or ski or when a snowmobiler stopped. Aune noted that, in general, animals function best in a predictable environment. Groomed routes, both for snowmobilers and skiers, create a more predictable environment. High cygnet mortality prior to fledging can to be related to the poor condition of nesting females following severe winters and/or late, cold springs. However, Maj (1983) found that mortality is more site- or pair-specific and not entirely related to the nutritional status of the laying female. Maj also noted that 130?190 days are required to lay an average clutch of five eggs, incubate the eggs to full term, and raise the cygnets to fledging. Limitations to breeding time may be an important factor in the GYA where only approximately 90 frostfree days occur each year. Drought conditions are also an important factor in cygnet mortality. Trumpeter swans in the GYA are particularly affected by human use of the following Potential Opportunity Areas as well as any opportunity area that has open water: (1) Destination areas (4) Groomed motorized routes (5) Motorized routes (6) Backcountry motorized areas (7) Groomed nonmotorized routes (8) Nonmotorized routes (9) Backcountry nonmotorized areas (12) Low-snow recreation area MANAGEMENT GUIDELINES Designating snowmobile and ski trails away from open waters used as winter habitat by swans can mitigate winter recreational impacts on the birds. Special restrictions may need to be implemented on open-water snowmobiling in areas that swans routinely use for feeding. These measures would reduce the energetic expenditures resulting from disturbance. Some concern has been raised about the effects of snowmobile noise on swans. At this time, no information is available on this subject. LITERATURE CITED Aune, K. 1981. Impacts of winter recreationists on wildlife in a portion of Yellowstone National Park, Wyoming. Thesis, Montana State University, Bozeman, Montana, USA. Banko, W. E. 1960. The trumpeter swan. University of Nebraska Press, Lincoln, Nebraska, USA. Ehrlich, P., D. Dobkin, and D. Wheye. 1988. The birder?s handbook: a field guide to the natural history of North American birds. Simon & Schuster, New York, New York, USA. Gale, R. S. 1989. Pages 59?60 in T. W. Clark, A. H. Harvey, R. D. Dorn, D. L. Genter, and C. Groves, editors. Rare, sensitive, and threatened species of the Greater Yellowstone Ecosystem. Northern Rockies Conservation Cooperative, Montana Natural Heritage Program, The Nature Conservancy, and Mountain West Environmental Services, Jackson, Wyoming, USA. Hensen, P., and T. A. Grant. 1991. The effects of human disturbance on trumpeter swan breeding behavior. Wildlife Society Bulletin 19:248?257. Maj. M. E. 1983. Analysis of trumpeter swan habitat on the Targhee National Forest of Idaho and Wyoming. Thesis, Montana State University, Bozeman, Montana, USA. NPS (National Park Service). 1996. Yellowstone Center for Resources 1995 Annual Report. Yellowstone National Park, Wyoming, USA. Reel, S., L. Shassberber, and W. Reudiger. 1989. Caring for our natural community. Region 1 threatened, endangered & sensitive species program. U.S. Forest Service, Northern Region, Missoula, Montana, USA. Shea. R. 1979. The ecology of the trumpeter swan in Yellowstone National Park and vicinity. Thesis, University of Montana, Missoula, Montana, USA. USFWS (U.S. Fish and Wildlife Service). 1996. Trumpeter swan survey of the Rocky Mountain population/U.S. flocks. Red Rock Lakes National Wildlife Refuge, Lakeview, Montana, USA. PREPARED BY: Tom Olliff, Management Biologist, National Park Service, Yellowstone National Park, Wyoming, USA. REVIEWED BY: Terry McEneaney, Bird Biologist, National Park Service, Yellowstone National Park, Wyoming, USA.

Keywords: animal, bird, swan, trumpeter swan, Olor buccinator, human activity, habitat, wildlife , management, population, mortality, bibliography, Greater Yellowstone Ecosystem, Yellowstone National Park, Targhee National Forest, Henry's Fork, Idaho, habitat, hunting, breeding, nest, nesting, behavior, migration, waterfowl, water bird, Anatidae