Effects of Early Water Application on Waterfowl Production

Abstract

Records of nests and broods on the Monte Vista National Wildlife Refuge, Colorado, suggested that waterfowl production was high in years when water was available prior to spring migration. If sufficient water was not available until after spring migration, low production could be expected. To test this hypothesis, we divided a 241-ha habitat unit on the Refuge into 2 plots; the experimental plot was flood-irrigated 2 weeks before the peak of spring waterfowl migration and the control plot was flood-irrigated 2 weeks after the peak of migration. This treatment was applied alternately to the plots during two 3-year periods and one 2-year period. Numbers of nests and production of mallards (Anas platyrhynchos), pintails (A. acuta), shovelers (A. clypeata), teals (A. discors, A. crecca, and A. cyanoptera), and gadwalls (A. strepera) were significantly greater (P < 0.05) on one plot when early water was applied. The inability to draw down water levels sufficiently on the other plot was believed to be the reason duck production was not significantly greater on both plots during years of early water application. Economic and management implications are presented. J. WILDL. MANAGE. 40(2):227-232 Nesting and brood observations on the Monte Vista National Wildlife Refuge in southwestern Colorado from 1953 through 1964 suggested that waterfowl production was higher when water was abundant prior to spring migration, or lower if water was not available in sufficient amounts until after migration. An 8-year study was initiated in 1965 to determine if early water application would (1) increase waterfowl production and (2) be economically feasible as a management practice. We are grateful to C. R. Bryant, Manager of the Monte Vista National Wildlife Refuge, and his staff, who were extremely helpl during the investigation. C. R. Bryant and R. M. Ballou, former Refuge biologist, conceived the basic study. Special thanks are g ven M. G. Sheldon and R. A. Ryder fo their assistance and suggestions. Assistance in many facets of the study was given by personnel of the U.S. Fish and Wildlife S vice, Colorado State University, and the Co orado Division of Wildlife. The study was financed by the Division of Wildlife Refuges, U.S. Fish and Wildlife Service, th ough the Colorado Cooperative Wildlife Research Unit.