Winter condition of mallards on the Southern High Plains of Texas
Mallards arriving on the Southern High Plains of Texas in the fall are in poorer condition, with less lipid and protein and lover body weights, than birds during the winter. Adults gained lipids and some protein and were heaviest in early and mid-winter, but juveniles did not show the same degree of gain. Whereas lipid gains were substantial, protein remained stable after the initial increase. Adult hens showed relatively greater lipid gains, and wintered in better condition than other mallards. Cold fronts and thermal stress in November did not affect lipid and body weight gains of adults. During late winter, mallards, except for juvenile drakes, depleted lipids for thermogenesis and lost weight when thermal stress was greatest. Cold fronts in January and February added to this effect. Estimates of mallard survival potential decreased by 1 day with each 10 degree Celsius drop in ambient temperature. Mortality of mallards on the Southern High Plains of Texas related to condition-stress was considered to be a minor factor in overall winter mortality. Mallards departed in the spring with high lipid reserves and heavy body weights Overall, mallards wintering in the region were in excellent condition between October and March, after the initial gains from their poor condition in the fall. Abundant waste-corn and intermittent cold fronts rather than prolonged cold spells allowed mallards to maintain this status. Condition indices were formulated for use in body condition assessment of mallards. Wet-skin weight was found to be the best predictor of mallard lipid reserves.