Northern Prairie Wildlife Research Center
Mark Willms and Rodney Sayler
Institute for Ecological Studies
Box 8278, Univ. of North Dakota
Grand Forks, North Dakota 58202
Brood hens from Mallard Island traveled significantly further (mean = 4.7 km) to reach brood-rearing wetlands than hens from Lake Audubon (mean = 3.0 km). Mallard broods traveled farther (mean = 5.0 km) than gadwall broods (mean = 2.0 km). Brood hens from Mallard Island required an average of 2.8 days to reach destination wetlands compared to an average 1.9 days for Lake Audubon brood hens. Mallard brood hens often used smaller, shallower, and more vegetation-filled wetlands for brood-rearing than gadwalls when they were available.
Duckling survival estimates for mallard and gadwall broods combined averaged 12% for birds produced from Mallard Island and 35% for birds from Lake Audubon. About 81% (17/21 from Mallard Island) and 30% (5/15 from Lake Audubon) of the unsuccessful brood hens lost all ducklings while enroute to a wetland. Duckling survival from Mallard Island averaged about 30% (25/83) in 1986 during a year of high water levels in the Garrison Reservoir, but declined to 0% (0/129) in 1987 when the reservoir was low and wide shorelines were exposed.
Our studies suggest that several environmental factors impact duckling survival rates in this large-reservoir environment (not necessarily in order of importance): 1) relatively large post-hatch travel requirements, 2) predation by gulls and mink (Mustela vison), 3) severe weather events during lake crossings, and 4) relatively low quality or productivity of wetlands adjacent to the reservoir. Management actions, such as predator control, wetland construction, and wetland management, are probably warranted to insure at least average productivity rates from large numbers of waterfowl attracted to these reservoir nesting islands.