Canada geese are true migrants, leaving their wintering grounds in the southern states of America for the breeding grounds in northern and central Canada. The important role of fats in vernal migration has been investigated in a large variety of passerine birds (see review by King 1972) and fats have been shown to be the major fuel for muscular energy (George and Berger 1966). The fat reserves of wintering, migrating, and moulting Canada geese have been studied quantitatively by Hanson (1962), who related the amount of fat in four distinct depots to the condition of the birds. Following migration to the breeding grounds, geese usually have to endure periods of low temperatures and adverse weather conditions before the onset of reproduction. Consequently geese must thermoregulate, and fat is believed to serve the dual function of being an insulator as well as a thermogenic substrate. Hanson (1962) reported a 6o%10 o loss in body weight of yearling geese in the first 31 weeks following their arrival on the breeding grounds, and incubating females weighed approximately 22%o less than when they arrived on the breeding grounds, both losses largely reflecting a depletion of fat. Egg production requires the diversion of lipids from the body, the production of four eggs requiring approximately 63-83 g of lipids (Romanoff and Romanoff 1949). Thus fats are actively involved in several different physiological processes between leaving the wintering grounds and completion of reproduction. Some studies on the lipid composition of migrant birds have shown that dietary lipids may exert a strong influence on the composition of body lipids (Nakamura 1962; Hicks 1967; Bower and Helms 1968; West and Peyton 1972; Johnston 1973; Morton and Liebman 1974), but West and Meng (1968a, 1968b) have indicated that factors other than diet per se may determine the composition of depot lipids. In the present study, Canada geese of the Eastern Prairie Population were collected at different stages of their life cycle, and the fatty acid composition of different lipid fractions from the adipose tissue and plasma was determined. Because lipids are involved in migratory flight as a source of muscular energy, in the development of testes, in egg production, and probably in thermogenesis, an attempt was made to determine whether the composition of
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