Bioenergetics and nutrition of Mississippi Valley population Canada geese during winter and migration

Survival and reproduction of northern-nesting geese are potentially affected by body condition during the non-breeding season. Body condition is presumed to be determined by the quantity of food available to geese during autumn, winter, and spring migration. However, food resources likely do not limit populations that exploit agricultural systems. Other factors such as hunting, refuge management, diet quality, and weather may affect survival and reproduction. We studied time-energy budgets, food intake, and body condition to determine how Canada geese (Branta canadensis interior) of the Mississippi Valley Population (MVP) acquire and utilize energy and nutrients during autumn, winter, and spring migration during 1984-1989. Abundant food and behavioral flexibility allowed MVP Canada geese to exist on a high nutritional plane. Food intake was sufficient to meet or exceed daily energy and protein requirements except during winter. High energy, low protein diets fueled deposition of large lipid reserves, and were adequate to meet protein requirements during autumn in east-central Wisconsin. Late migrant geese that spent autumn in east-central Wisconsin expended more energy (x = 583 kcal/day) yet deposited more lipid (x = 451 g) compared to early migrants that spent autumn in southern Illinois (x = 526 kcal/day, x = 151 g lipid) during 1984 and 1985. Both groups averaged 4.5 hr feeding/day during autumn and consumed similar quantities (dry mass) of food (x = 187-190 g/day). However, late migrants consumed a high energy (x = 3.67 kcal/g) low protein (x = 12%) diet comprised mostly of corn (x = 81%) during autumn in east-central Wisconsin. Early migrants consumed a lower energy (f = 2.99 kcal/g) but higher protein (24%) diet that consisted mostly of green forages (x = 24% dry mass) and soybeans (x = 28%) in southern Illinois. Wintering geese consumed a high energy (x = 3.49 kcal/g) diet with intermediate protein content (x = 19%). Corn (x = 58%) and soybeans (x = 22%) comprised most of dry matter intake during winter in southern Illinois when daily energy expenditure averaged 536 kcal/day. However, food intake declined (x = 152 g food/ day) during winter when geese averaged 3.5 hr feeding/day. Variation in crop food energy relative to population energy requirements on 2 southern Illinois refuges did not impact body condition during 1984-1989. Nutrient reserves contributed minimally (<1-6%) to meeting daily energy requirements, so geese left winter refuges with more lipid and similar protein masses compared to early autumn. Geese exhibited a wide range of behavioral adaptation to spatial and temporal variation in food resources and nutritional requirements. Late migrants entered winter with larger energy reserves than early migrants during 1984-1989. Although early and late migrants were sympatric in southern Illinois during winter, they converged to similar levels of body condition by the end of winter during 1986-1989. Late migrants apparently used stored energy to reduce food intake, possibly to minimize mortality during winter. Early migrants apparently minimized exposure to hunting by feeding almost entirely within refuges during autumn. With smaller energy reserves, early migrants maintained higher levels of energy intake to maintain body condition after autumn, possibly increasing mortality risk during winter.