Decline of Northern Pintails

Decline of Northern Pintails
		by *Jay B. Hestbeck* National Biological Service

Fig. 1. Number of pintails in northern areas from Alaska to northern Alberta and northern Manitoba and in the prairie region from southern Alberta and central Montana to southern Manitoba and the Dakotas from 1955 to 1993 (Breeding Population and Habitat Survey, U.S. Fish and Wildlife Service, Office of Migratory Bird Management).

The size of the continental breeding population of northern pintail (Anas acuta) has greatly varied since 1955, with numbers in surveyed areas ranging from a high of 9.9 million in 1956 to a low of 1.8 million in 1991. This variation results primarily from differences in the numbers of breeding pintails in the prairie region of Canada and the United States (Fig. 1); these numbers ranged from 8.6 million in 1956 to 0.5 million in 1991; numbers in the northern regions from Alaska to northern Alberta and northern Manitoba varied primarily between 1 and 2 million.

Breeding pintails prefer seasonal shallow-water habitats without tall emergent aquatic vegetation (Smith 1968). The proportions and distribution of breeding pintails on the prairies vary annually depending on the amount of annual precipitation and the resulting increase or decrease in the availability of suitable breeding habitat (Smith 1970; Johnson and Grier 1988).
Changes in the size of the continental pintail population result from changes in production, survival, or both. Consequently, understanding population changes involves detecting variation in survival and production over time and relating that variation to changes in population size. Once the cause of the decline is determined, appropriate management strategies can be developed to reverse it.
Status and Trends

Pintails (Anas acuta). Courtesy J.B. Hestback

I arbitrarily partitioned the population data into periods of relative growth, stability, and decline to help explain changes in the continental breeding population, which declined from 1955 to 1962, increased from 1963 to 1970, remained at a high stable level from 1971 to 1979, and declined from 1980 to 1992. I also partitioned the continental population into flyways based on data from recoveries of winter-banded pintails. This data indicated that pintails exhibit a high fidelity to the winter-banding region and flyway (Hestbeck 1993). Data from recoveries of summer-banded pintails were used to associate birds between breeding and wintering areas.

Data on the pintail population were obtained through various surveys conducted by the United States and Canada. The Breeding Population and Habitat Survey provided estimates for the number of breeding pintails and for the total number of ponds. The total number of ponds was used as an index of breeding-habitat availability where the availability increased as the number of ponds increased. Annual survival rates were estimated from legband recoveries of summer-banded pintails.
I estimated average survival rates for the previously listed time periods for all areas with banding data. As an index of production, I used the number of young females divided by the number of adult females (i.e., age-ratio) harvested annually in each flyway reported in the Waterfowl Parts Collection Survey (U.S. Fish and Wildlife Service, Office of Migratory Bird Management). Because of possible harvest differences among flyways and large variation in annual ratios, I estimated the average age-ratio for each flyway for the above time periods.
Changes in the continental population can be addressed by studying changes in flyway populations because pintails from different summer breeding areas were associated with certain wintering areas. Generally, pintails wintering in the Pacific Flyway were associated with breeding areas in the western states and provinces from Alaska to Saskatchewan and central Montana. Pintails in the Central Flyway were primarily associated with breeding areas in Saskatchewan, eastern Montana, Manitoba, and the Dakotas. Pintails in the Mississippi Flyway were primarily associated with breeding areas from Saskatchewan and Minnesota to James Bay. Pintails in the Atlantic Flyway were primarily associated with breeding areas from James Bay to the Canadian Maritimes.

Fig. 2. Average production of pintails in Atlantic, Mississippi, Central, and Pacific flyways for 1963-70, 1971-79, and 1980-92 (Waterfowl Parts Collection Survey, U.S. Fish and Wildlife Service, Office of Migratory Bird Management).

If 1980-92 population declines were caused by poor reproduction, production would be lower. Production, however, remained relatively constant over periods of population growth (1963-70), stability (1971-79), and decline (1980-92) for the Atlantic, Mississippi, and Central flyways (Fig. 2). Production in the Pacific Flyway exhibited a substantial decline from 2.40 in 1963-70, to 1.78 in 1971-79, and to 1.60 in 1980-92.

Likewise, survival would be lower during 1980-92 if population declines were caused by declines in survival. Comparisons of average survival rates between 1980-92 and earlier periods were possible for only a limited number of areas because few pintails were banded in many regions. In the area encompassing northern Alberta, northeastern British Columbia, and southwestern Northwest Territories, average survival during 1980-92 was higher than the average for earlier periods for adult males (80% versus 68%), young males (68% versus 53%), and adult females (69% versus 64%). In southern Alberta, average survival during 1980-92 was higher than the average for earlier periods for adult males (74% versus 70%) and young females (86% versus 55%). Survival remained constant between 1980-92 and earlier periods for all age-classes of pintails banded in southern Saskatchewan and southern Manitoba. In the Dakotas, average survival during 1980-92 was higher for only adult males (77% versus 66%).
These data reveal that possible declines in pintail survival did not cause the population declines observed during the 1980's. Overall, survival was higher during 1980-92 than during earlier periods for adult males that winter in the Pacific, Central, and Mississippi flyways and for young females that winter in the Pacific Flyway. Survival remained constant between time periods for adult females and young males in the Pacific, Central, and Mississippi flyways.
Given the small changes in production and survival, pintail numbers should stabilize in the Central and Mississippi flyways and possibly the Atlantic Flyway. In the Pacific Flyway, however, the survival increases of young females has not compensated for the overall decrease in production.
During the 1980's the Canadian prairies on the average received less precipitation, resulting in reduced availability of pintail breeding habitat. Hopes for increased pintail population size have been based, in part, on the expectation that increased precipitation in the western Canadian prairies would result in increased breeding habitat and production. Female-based age-ratio data suggest, though, that increased production is unlikely to occur even with increased precipitation because pintail production remained low even when water was plentiful. Average age-ratios for the Pacific Flyway when water in the western Canadian prairies was above average (total May ponds for southern Alberta and southern Saskatchewan exceeding 2.68 million) steadily declined from 3.11 in the 1960's, to 2.03 in the 1970's, and 1.86 in the 1980's.
Consequently, a fundamental change appears to have occurred in pintail productivity on western Canadian prairies, meaning that we cannot base pintail management on the hope that increased precipitation will result in a return to the higher levels of production experienced in the 1960's.
Researchers suspect that the production decline may be related to the fact that the shallow-water breeding habitat favored by pintails is most susceptible to agricultural drainage. By 1989, 78% of the pothole margins (the transition zone where potholes meet farmland) and 22% of wet basins were degraded by agricultural activity in prairie Canada (F.D. Caswell and A. Didiuk, Canadian Wildlife Service, personal communication). Increased intensification of agriculture may also contribute to lower production on the prairies through increased grazing and cropping, increased nest destruction, and increased use of agricultural chemicals (Ducks Unlimited 1990). Further research on the western Canadian prairies is necessary to determine specific causes of production declines in pintails and to determine methods to increase production.
		For further information: Jay B. Hestbeck National Biological Service Cooperative Fish and Wildlife Research Unit University of Massachusetts Amherst, MA 01003

References
Ducks Unlimited. 1990. Sprig: population recovery strategy for the northern pintail. Ducks Unlimited, Inc., Long Grove, IL. 30 pp. Hestbeck, J.B. 1993. Overwinter distribution of northern pintail populations in North America. Journal of Wildlife Management 57:582-589.	Johnson, D.H., and J.W. Grier. 1988. Determinants of breeding distributions of ducks. Wildlife Monograph 100. 37 pp. Smith, R.I. 1968. The social aspects of reproductive behavior in the pintail. Auk 85:381-396. Smith, R.I. 1970. Response of pintail breeding populations to drought. Journal of Wildlife Management 34:943-946.

Decline of Northern Pintails

Status and Trends