Population energetics of northern pintails wintering in the Sacramento Valley, California

Recovery of northern pintail (Anas acuta) breeding populations may be facil itated by improved management of ti winter food and habitat resources. We e stimated daily energy expenditure (DEE) of pintails, which included energy required from food and carcass reserves (DERfood, DERreserves), from mid-Au gust to mid-March during a dry (1980-81) and a wet (1981-82) winter in the Sacramento Valley, California, using equations for existence metabolism (EM ; kJ/day) and estimates of body mass, carcass composition, food habits, and apparent metabolizable energy (AME) of Minter foods. We used these values and food density (kg/ha) to model population food and habitat (ha) requirem ents, Predicted DEE by monthly period ranged from 794 to 1,180 kJ/day for m ales and 700 to 1,044 kJ/day for females. Pintails consumed a predicted 49- 82 g of food/day from wetlands and rice fields. The DEE was highest in Sept ember-October ol October-November and again in January-February and DERrese rves was greater during November-December or December-January (up to 11.6% of DEE), and during the dry winter. Total food consumed by the larger pinta il population present in the wet winter of 1981-82 exceeded that of the sma ller population in the dry winter of 1980-81, both from wetlands (2.89 vs. 2.52 million kg) and harvested rice fields (11.4 vs. 9.37 million kg). Like wise, the cumulative area of wetlands and rice fields used to provide food was greater in the wet (2,060 ha of wetlands, 41,456 ha of rice fields) tha n dry winter (1,782 ha of wetlands, 33,941 ha of rice fields): these totals accounted for up to 23% of available rice fields and 9% of available wetla nds. Population food and habitat requirements peaked in December-January co inciding with peak pintail populations but not peak DEE (Tan-Feb), Model ou tcomes were most sensitive to variation in food density AME, percentage of food obtained from wetlands and rice fields, and pintail abundance. Food an d habitat seemed adequate for pintail populations wintering in the Sacramen to Valley in the 1980s and presently; however, this conclusion must be vali dated by modeling bioenergetic requirements for other abundant waterfowl an d wildlife that forage in 1 ice fields and wetlands in this region.