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Population Energetics of Northern Pintails
Wintering in the Sacramento Valley, California

Introduction


In spring 1998, the continental breeding population of northern pintails (hereafter, pintail) was 55% below the objective of 5.6 million (U.S. Fish and Wildlife Service et al. 1994) and 43% below the long-term mean (U.S. Fish and Wildlife Service 1998). Despite current low number, the pintail is the most abundant waterfowl species wintering in California, and the majority are found in the Sacramento Valley (Bellrose 1980:267). Pintails arrive there in early August, increase to approximately 1.5 million birds by midwinter, and remain abundant until March (Miller 1985, 1986b). This population requires abundant food to support energy expenditures for body mass gain (Miller 1986b), molt (Miller 1986a), pair formation, and other activities (Miller 1985).

Pintails in the Sacramento Valley obtain food from managed wetlands and harvested rice fields (Miller 1987), but the capacity of these habitats to sustain local wintering populations has not been assessed. Lack of food resources may limit pintail body condition in dry winters (Miller 1986b), and winter wetland conditions may affect recruitment (Raveling and Heitmeyer 1989). Thus, there is need to quantify food and habitat required to support wintering pintails to guide habitat conservation (Central Valley Habitat Joint Venture 1990). Our objective was to predict these requirements by conducting a population energetics analysis for pintails wintering in the Sacramento Valley during a dry and a wet winter. We constructed a population energetics model, which consisted of estimates of DEE of individual pintails integrated with population size and dynamics (Wiens and Farmer 1996), and we assessed its applicability to predict winter food and habitat needs under the historical range of pintail abundance.


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