Winter Condition of Mallards on the Southern High Plains of Texas

Abstract

Body composition and condition of mallards (Anas platyrhynchos) wintering on the Southern High Plains (SHP) of Texas were studied from October to March 1979-82. Lipid reserves, and usually body weights, of all sex and age classes were lowest in autumn. By mid-winter, however, lipid reserves increased 49-62% for adults and 21-30% for juveniles and averaged 13-18% of body weight. The majority of these reserves (56-100%) were acquired from autumn to early winter. Adults and juvenile females then lost lipids from mid-winter to late winter (9-15%), but juvenile males increased reserves by 20%. Adult females mobilized more lipids than adult males during late winter (15 vs. 9%) and previously had acquired a larger reserve (20 vs. 7%). Body weight and lipids increased before spring migration. Overall, mallards on the SHP maintained better condition than those wintering farther north. J. WILDL. MANAGE. 50(1):52-57 Body weight and carcass composition of waterfowl are not stable during winter (Peterson and Ellarson 1979, Raveling 1979, Reinecke et al. 1982). These changes may be influenced by body condition, which has been defined as an individual's ability to meet present and future needs (Owen and Cook 1977). In this paper we refer to condition as the relationship between an individual's endogenous energy reserves and energy demands for maintenance, productivity, and activity. The SHP of Texas is an agricultural region where wintering mallards have adopted a fieldfeeding strategy; they join northern pintails (A. acuta), American wigeons (A. americana), and green-winged teal (A. crecca) in morning and evening field-feeding flights for waste corn (Baldassarre and Bolen 1984). More than 90% of the diet, by volume, consisted of corn during a 2-year study sampling 324 mallard crops and gizzards (Moore 1980). Corn is higher in energy than seeds of native plants occurring in the numerous playa lakes that serve as wetland habitat for waterfowl on the SHP (Baldassarre et al. 1983). This high energy content influences body condition as available carbohydrates are converted into endogenous lipids (Hazelwood 1976). Lipids, in turn, become important reserves used by birds during periods of winter stress (Blem 1976). However, although mallards wintering on the SHP have access to high energy foods, they also encounter temperature stress during certain periods (Whyte and Bolen 1984). The objective of this study was to determine the relationship between winter stress and carcass composition, especially lipid reserves, of mallards wintering on the SHP. Financial support was provided by the Caesar Kleberg Found. Wildl. Conserv. and the U.S. For. Serv. (F. A. Stormer, Proj. Leader, Great Plains Wildl. Habitat Res. Lab.). J. D. Myrick, J. R. Davis, C. L. Lee, H. A. McLain, D. W. Brown, W. J. Hill, and T. J. Hill granted access to private property. R. J. Baker, K. T. Scribner, J. J. Juen, E. E. Quinlan, G. E. Huber, R. H. Lunn, and R. D. Godfrey aided collection of mallards during hunting seasons. R. D. Godfrey, J. A. Templer, and J. J. Peterson assisted with laboratory work. L. J. Celentano and D. B. Webster provided advice during statistical and computer analysis of the data. We are grateful to all. This is contribution T-9-370 of the Coll. Agric. Sci., Texas Tech Univ., Lubbock.