Mortality in Crippled Mallards

Radio-equipped crippled mallards (Anas platyrhynchos) were followed on the Horicon National Wildlife Refuge, Wisconsin, during 2 successive waterfowl hunting seasons to develop a more precise estimate and understanding of crippling loss. Cripples without radios were kept concurrently in a pen. Healing of released cripples was rare (3%) and not correlated with any observed environmental or behavioral variables. The distribution of shallow-water areas where cripples fed and rested influenced the cripples' proximity and accessibility to predators and, thereby, influenced the timing and agent of mortality. Weight loss contributed directly or indirectly to the mortality of most cripples. Healing of cripples was more frequent (23%, P < 0.05) in the pen than in the wild, because of adequate food, minimal disturbance and movement, and absence of predators. The number of cripples that heal is probably insignificant at the population level. The best avenue to reduce mortality associated with crippling loss is to reduce the crippling loss rate.