The role of predator removal and density-dependence on mallard production in northeastern North Dakota

Abstract

Density-dependence is a central tenet of wildlife population dynamics and harvest management, yet the pathways and mechanisms by which density-dependence operates remain unclear. In 1994, Delta Waterfowl Foundation began trapping meso-predators in northeastern North Dakota to determine if it was a viable technique for increasing waterfowl production. Subsequent research on replicated experimental sites found that trapping predators increased nest success by about 2-fold, and nest success was the most important factor regulating population growth in previous studies of midcontinent mallards. Given the philopatric nature of most waterfowl species, higher nest success on trapped sites was predicted to lead to 36% greater annual population growth on trapped sites versus controls, which should have led to doubling of pair densities approximately every two years. This backdrop provided me with the unique opportunity to examine the role of density-dependence on waterfowl production at a local scale in North Dakota. My dissertation focuses on the role of density-dependence and predator removal on mallard duckling survival, duckling body condition, and overall mallard productivity in northeastern North Dakota from 2006-2007. Contrary to predictions, predator removal had no beneficial effect on mallard duckling survival. Duckling density was weakly negatively associated with mallard duckling survival, but had no effect on duckling condition. Duckling survival, not nest success, was the most important factor influencing population growth and production and appeared to be functioning as the key limiting factor in our populations. Overall, predator removal did not lead to local population increases on trapped sites and added far fewer incremental ducks to the fall flight than originally predicted. The perils of duck hunting are great - especially for the duck. - Walter Cronkite.