Wintering Canada Geese in the Willamette Valley

Only about 2,500 Canada geese wintered in the southern Willamette Valley between 1938 and 1948 (Gullion 1951), but during the subsequent 20 years, the size of the valley population greatly increased (Fig. 1). The U.S. Fish and Wildlife Service (Region 1, Portland, Oregon) began systematic surveys of wintering Canada geese in 1953 when the peak count was fewer than 10,000 birds. The typical winter population increased to about 20,000 birds by 1967. Throughout this period most of the geese counted were dusky Canada geese (Fig. 2). The southern Willamette Valley was the major harvest area for dusky Canada geese in the early 1950's (Chapman et al. 1969). In the mid-1960's, three national wildlife refuges were established to provide the geese with some refuge from hunting.

The winter abundance of dusky Canada geese in the Willamette Valley began to decline in the 1980's because of long-term ecological changes that occurred on the birds' nesting grounds in Alaska. In 1964 an earthquake on the Copper River Delta lifted the nesting grounds 0.5-2 meters (Shepherd 1965) and caused the habitat to change from tidal wetlands to uplands. Predation of nests by grizzly bears, coyotes, bald eagles, and mew gulls subsequently increased. By the 1980's nest productivity had significantly declined, leading to a population decline that continues today (Campbell 1992).

In the late 1960's, Taverner's Canada goose, a smaller subspecies that nests in arctic Alaska and Canada, began wintering in the Willamette Valley and greatly complicated management of geese in the valley. As the population of dusky Canada geese began to decline, the winter population size of Taverner's Canada geese increased exponentially during the mid-1970's and early 1980's (Jarvis and Cornely 1985). Managers were faced with the dilemma of protecting a declining subspecies threatened by changes on their breeding grounds, while the size of another subspecies population was rapidly expanding to the point of providing a considerable surplus for harvest. Moreover, certain behavioral tendencies of dusky Canada geese make them particularly vulnerable to hunters (Simpson and Jarvis 1979).

Low numbers of a third subspecies, the cackling Canada goose, wintered at the northern end of the Willamette Valley in the mid-1960's (Chapman et al. 1969), but most individuals wintered in the Central Valley of California. The population size of this subspecies subsequently declined precipitously, resulting in a flyway-wide hunting closure from 1984 to 1993. During the mid-1980's, the cackling Canada goose remained an insignificant part of the winter population of Canada geese in the Willamette Valley. The population size of this subspecies greatly increased during the last decade, however; the current winter population is about 60,000 birds. Four other subspecies also contribute to the winter population in the Willamette Valley: Vancouver Canada goose, the federally threatened Aleutian Canada goose, western Canada goose, and lesser Canada goose. Thus, 7 of the 11 recognized subspecies of Canada goose in North America (Delacour 1954) winter in the Willamette Valley. Moreover, the western Canada goose began nesting in the valley about 20 years ago and its nesting population continues to increase.

All subspecies of Canada goose that winter in the Willamette Valley graze on green vegetation. Numerous types of grass and clover are planted by valley farmers. The area planted in grasses for seed in the Willamette Valley changed from limited amounts in the 1950's to about 160,000 hectares in 1993 (Fig. 3). Estimates of grass seed production steadily increased from 13,900 to 243,300 metric tons from 1940 to 1990 (Oregon State University Extension Service, Corvallis, unpublished data). Modern farm practices steadily improved yields and this, in turn, probably resulted in increasing forage potential for wintering geese. The cultivated grasses grow during the winter and provide fresh green vegetation, whereas most native plants are dormant in winter and do not provide forage for grazing geese.

The fact that Canada geese now winter farther north than before is not unique to the Willamette Valley; similar situations occur in northern portions of the Mississippi and Atlantic flyways. As a consequence, the Willamette Valley now supports about ten times more geese in winter than it did 40 years ago.