Fat deposition and usage by arctic-nesting sandhill cranes during spring

Body weight, fat, and protein levels of arctic-nesting Sandhill Cranes (Grus canadensis) were measured at several locations during spring migration and on the breeding grounds. Body weights of adult males and females increased by about 34% (1,129 g) and 30% (953 g) from early March at the Platte River to late April at Last Mountain Lake, Saskatchewan; average fat content increased from about 250 to 990 g. Rates of weight gain and fat deposition among males and females averaged 25-18 and 16-13 g/day. Body weights and fat content of cranes staging along the North Platte River followed similar patterns and usually were higher than along the Platte River during comparable periods. Fat reserves of paired cranes collected after their arrival at a major breeding ground on the Yukon-Kuskokwim Delta in western Alaska averaged about 530 g, or about 46% less than peak fat content in Saskatchewan. Patterns of weight increase and fat deposition in cranes during migration were similar to those previously described for northern-nesting geese, except that nutrient storage is not sex specific in cranes. Body protein of adult female cranes did not change significantly during spring migration (P = 0.28). Female cranes allocate less nutrients to clutch formation in proportion to body size than do northern-nesting geese.