Northern Pintail Body Condition during Wet and Dry Winters in the Sacramento Valley, California

Body weights and carcass composition of male and female adult northern pintails (Anas acuta) were investigated in the Sacramento Valley, California, from August to March 1979-82. Pintails were lightweight, lean, and had reduced breast, leg, and heart muscles during August-September. Ducks steadily gained weight after arrival; and body, carcass (body wt minus feathers and gastrointestinal content), fat, protein, and muscle weights peaked in October-November. Fat-free dry weight remained high but variable the rest of the winter, whereas body and carcass weight and fat content declined to lows in December or January, then increased again in February or March. Gizzard weights declined from early fall to March. Males were always heavier than females, but females were fatter (percentage) than males during mid-winter. Mid-winter body weight, carcass fat, and protein content were significantly (P 300,000 are present by mid-September (LeDonne 1980), and about 1 million are present in mid-winter (Bellrose 1980:267). Pintails are the most abundant waterfowl species in California during winter, and wetland habitat and agricultural food resources must sustain this large number of ducks well into March. However, wetlands have been destroyed at an accelerated rate in recent years (Gilmer et al. 1982), placing great importance on decisions for managing remaining habitat. Dynamics of physical condition (carcass fat and protein) during winter is related to food supply (Ryan 1972, Owen and Cook 1977), which can be a function of habitat management (Chabreck 1979) or flooding induced by rainfall (Chabreck 1979, Fredrickson 1980, Heitmeyer and Fredrickson 1982). Ideally, winter habitat provides food to ensure that ducks leave wintering grounds in condition adequate to support needs during migration and nesting. The objective of this study was to determine This content downloaded from 207.46.13.128 on Wed, 07 Sep 2016 06:22:57 UTC All use subject to http://about.jstor.org/terms 190 PINTAIL BODY CONDITION * Miller J. Wildl. Manage. 50(2):1986 Table 1. Total and normal monthly precipitation (cm) at Sacramento, California.