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Effects of Skunk Control on Duck Nest Success
in Western Montana

NATHAN E. HALL AND I. J. BALL

Montana Cooperative Wildlife Research Unit, University of Montana,
Missoula, MT 59812

This study was conducted in glaciated pothole habitat of the lower Flathead Valley in west-central Montana. The area is similar to much of the Prairie Pothole Region in topography, hydrology, land use, high nest predation rates, and faltering duck populations. Striped skunks were numerous and were the primary mammalian nest predator. Coyotes were common, but red foxes and raccoons were uncommon. Nesting studies conducted in the Ninepipe area in 1986 and 1987 provided baseline information on nest success with habitat management (the provision of dense nesting cover). Mayfield estimates of nest success for all species of upland-nesting ducks averaged 22%, with no significant difference between years. Nest success of mallards was 10% both years, comparable to recent rates in much of the Prairie Pothole Region, and well below the 15% level theoretically needed to maintain populations. A skunk removal program was initiated in the spring of 1988 on a 50-km² area of federal, state, tribal, and private lands surrounding Ninepipe National Wildlife Refuge. Although 109 skunks were removed, nest success did not change significantly (19%). During 1989, trapping began earlier and intensity was doubled on the key nesting areas, resulting in the removal of 77 skunks. Nest success increased significantly to 44% from the 1986-88 average (19%). Mallard nest success increased nearly four-fold from 10% in 1986-88 to 37% in 1989. Pablo National Wildlife Refuge served as an experimental control (non-removal) area. Nest success there did not differ significantly among years (GIF -- mean symbol=29%), although the analysis was hampered by small sample sizes. Improved nest success at Ninepipe in 1989 should result in increased homing by hens, and be reflected in higher nest densities in 1990. We will report on the outcome of this prediction and other aspects of the 1990 season at the symposium.
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