Nest-Site Distribution and Overland Brood Movements of Northern Pintails in Alberta

Abstract

Distribution of nests of northern pintails (Anas acuta) was examined around shallow waterbodies on grazed, mixed prairie in southern Alberta. Pintails were the most common ducks nesting on the mainland prairie but not on the more densely vegetated artificial islands. Nest density on the islands for pintails (10.4/ ha) and all duck species combined (80.0/ha) was much greater than that on the mainland (pintails = 0.160.17/ha and all = 0.26-0.31/ha). Hatching sucess of pintail nests on the prairie appeared to be relatively high, probably a result of nests being widely dispersed over large areas of suitable habitat. Pintail nests on the prairie were most commonly situated 1-2 km from water. A hypothesis that pintails nest far from water to avoid male-chasing was repudiated in favor of one that such behavior reduces nest predation. Substantial overland travel by pintail broods is common, necessitated by the distance that hens nest from water. Simulated 3-km nest-to-water movements of pintail ducklings did not deplete their lipid reserves or impair growth. J. WILDL. MANAGE. 51(4):716-723 The importance of prairie breeding habitat to the overall productivity of northern pintails is evidenced by the low apparent reproductive output of arctic-nesting birds (Calverley and Boag 1977, Derksen and Eldridge 1980) and the positive correlation between continental recruitment and the relative proportion of birds inhabiting the prairies (Smith 1970). Within the prairies, the grasslands of southern Alberta support higher densities of breeding pintails than any other region (Vermeer 1972, Bellrose 1979). Much of this area is rangeland, and consequently, many of the birds breeding there nest on grazed prairie. Most information on the location of nest sites of pintails has come from Manitoba and North Dakota where pintails frequently nest, often unsuccessfully, in cultivated fields (Sowls 1955:66, Milonski 1958, Higgins 1977, Krapu 1977). Pintails reportedly nest farther from water than other ducks (Keith 1961, Bellrose 1980: 271), but no systematic searches have been conducted to determine the distribution of their nests relative to water. Nests placed far from water are often thought to result in reduced duckling survival because of the extended overland travel required to get to water; e.g., Sayler 1962, Dzubin and Gollop 1972. In areas where artificial islands have been created, the distribution of nests on the mainland can be compared to that on islands to evaluate the efficacy of the islands in increasing waterfowl production. This study examined the location of pintail nests around a number of shallow basins in grazed prairie near Brooks, Alberta. Pintail use of artificial islands for nesting sites was compared to that of the mainland and contrasted with that of other duck species. The distance of pintail nests from water was determined, and the hypothesis that male pursuit flights cause hens to nest far from water was considered. The consequences of nesting far from water were examined, particularly the effect of overland movement on the condition of ducklings. Financial support of this study was provided by grants to D. A. Boag from the Nat. Sci. and Eng. Res. Counc., and Can. Natl. Sportmen's Fund. Ducks Unlimited Can. and the Brooks Wildl. Cent. of the Gov. Alberta provided invaluable logistic support. Thanks to T. S. Coleman, R. Cotter, G. G. Gregoire, A. J. Murphy, and T. D. Sorochan for their assistance in the field. Special thanks to D. A. Boag for his comments on the manuscript and also to C. D. Ankney, S. J. Hannon, V. Lewin, A. R. Palmer, A. Shires, W. D. Wishart, and P. M. Woodard. The Bamfield Mar. Stn. provided the facilities and personal support for revision of this paper. STUDY AREA AND METHODS The study was conducted in an area of grazed prairie about 35 km southeast of Brooks, Alberta, from 1981 to 1984. The study area included 4 impoundments that are managed for waterfowl production by Ducks Unlimited, Canada. These impoundments (Tilley O, Tilley P, Kininvie F, and Kininvie S) were described by Giroux (1981). At high water levels, the areas Present address: Bamfield Marine Station, Box 99, Bamfield, British Columbia VOR 1BO, Canada.