Changes in Diet and Body Composition of Canada Geese before Spring Migration

Abstract

Changes in diet and body composition of Giant Canada Geese (Branta canadensis maxima) were studied before geese initiated spring migration in early April. During the period of hyperphagia in March, body weight of female and male geese increased 36% and 26%, respec- tively, above average winter weights. Body weights of paired geese averaged 0.34 kg (females) and 0.27 kg (males) more than those of geese without mates before the weight gain period. Some unmated geese did not gain weight, and others gained less weight than paired geese. Geese shifted from a winter diet of corn (Zea mays) to a diversity of food items in spring. Corn remained the primary source of carbohydrate, and bluegrass (Poa pratensis) provided protein for geese. Weight gain of females was composed of 61% lipid, 10% protein, and 21% water, whereas weight gained by males was 47% lipid, 13% protein, and 35% water. Initial weight gains were predominantly protein (and accompanying water), probably required for gut enlargement. Most of the later body weight gain was due to lipid storage. Increase in size of breast and leg muscles at the end of March was largely due to lipid storage and a shift of protein from other body tissues. Lipid and protein storage was adequate to explain energy and nutrient requirements for body maintenance after arrival on the breeding grounds, egg laying, and territorial defense. Females may have to obtain minerals (and possibly additional protein) for egg formation from food sources on the breeding grounds. Lipid reserves of male Giant Canada Geese indicate an ability to sustain energetic costs during nesting equal to those of the female (apart from egg laying) and are greater than reserves of other species of geese and subspecies of Canada Geese investigated to date. Received 22 April 1980, accepted 21 August 1980. THE importance of lipid and protein reserves for reproduction by geese has been the subject of much recent discussion (Ankney 1977; Raveling and Lumsden 1977; Ankney and Macinnes 1978; Raveling 1978a, 1979a, b). Increases in body weight of females in spring of 41-53% of winter weight have been documented for Todd's Canada Goose (Branta canadensis interior, Hanson 1962a), Ross' Goose (Chen rossii, Ryder 1967), Lesser Snow Goose (Chen caerulescens caerulescens; Ankney 1977, Ankney and Macinnes 1978), and the Cackling Goose (B.c. minima, Raveling 1979a). These reserves provide the necessary energy for migration and reproduction and are critical in affecting clutch size. The evolutionary and functional significance of these weight gains was discussed in the papers cited above (see also Barry 1962, Ryder 1970). Few data exist on the process of acquisition of maximum body weights by geese during spring, however, and most previous studies used qualitative mea- sures or indirect indices of body composition of free-living geese (Hanson 1962a, Ryder 1970, Ankney 1977, Ankney and Macinnes 1978, Wypkema and Ankney 1979). Recently, body components were quantified and energetic strategies discussed for Common Eiders (Somateria mollissima, Korschgen 1977) and Cackling Geese (Raveling 1979a, b). The purpose of this study was to use similar methods to measure quantitatively the changes in body constituents and skeletal muscles undergone by adult Giant Canada Geese (B.c. maxima, Hanson 1965). We related these changes to food habits, social status, and timing of spring migration in order to understand better the behavior attendant to and the factors controlling the attainment of the annual reproductive state.