38 



Birds — Our Livin-j Resources 



Decline of 



Northern 



Pintails 



by 



Jay B. Hesthack 



National Biological Service 



Fig. 1. Number ot 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 froin IQ55 to 

 1993 (Breeding Population and 

 Habitat Sur\ey. U.S. Fish and 

 Wildlife Service. Office of 

 Migratory Bird Management). 



The size of the continental breeding popiilu- 

 lion of noilhem pintail {Anas acuta) has 

 greatly varied since 1955, with numbers in sur- 

 veyed 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 breed- 

 ing 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 

 piipulation changes involves detecting variation 

 in survi\'al and production over time and relat- 

 ing that variatiim to changes in population size. 

 Once the cause of the decline is determined, 

 appropriate management strategies can be 

 dcxeloped to reverse it. 



Northern areas 



54 57 60 63 66 69 72 75 78 81 84 87 90 93 

 Year 



Status and Trends 



I arbitrarily partitioned the population data 

 into periods of relative growth, stability, and 

 decline to help explain changes in the continen- 

 tal 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 fly- 

 ways based on data from recoveries of winter- 

 banded pintails. This data indicated that pintails 

 exhibit a high fidelity to the winter-banding 

 region and tlyway (Hestbeck 1993). Data from 

 recoveries of summer-banded pintails were 

 used to associate birds between breeding and 



Pintails i,-\//(n ,/r itiii I 



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 esti- 

 mates 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-habi- 

 tat availability where the availability increased 

 as the number of ponds increased. Annual sur- 

 vival rates were estimated from legband recov- 

 eries of summer-banded pintails. 



I estimated average survival rates for the pre- 

 viously listed time periods for all areas with 

 banding data. As an index of production, 1 used 

 the number of young females divided by the 

 number of adult females (i.e., age-ratio) har- 

 vested annually in each tlyway reported in the 

 Waterfowl Parts Collection Survey (U.S. Fish 

 and Wildlife Service. Office of Migratory Bird 

 Management). Because of possible harvest dif- 

 ferences among tlyways and large variation in 

 annual ratios. I estimated the average age-ratio 

 for each llyway for the above time periods. 



Changes in the condnental population can be 

 addressed by studying changes in tlyway popu- 

 lations because pintails from different summer 

 breeding areas were associated with certain 

 wintering areas. Generally, pintails wintering in 

 the Pacific Flyway were associated with breed- 

 ing 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 pri- 

 marily associated with breeding areas from 

 James Bay to the Canadian Maritimes. 



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 



