PIERCE, B.J.; MCWILLIAMS, S.R.*; Univ. Rhode Island, Kingston; Univ. Rhode Island, Kingston: Seasonal changes in the fatty acid composition of lipid stores in migratory birds: the relative importance of selective metabolism of fatty acids and behavioral preferences for certain dietary fatty acids.

Fatty acid composition of body fat in migratory birds changes seasonally and changes in diet may be responsible for the observed seasonal patterns. Alternatively, migratory birds may selectively metabolize and store certain fatty acids during migration in lieu of changing their diet. We tested these two hypotheses by maintaining captive red-eyed vireos on one of two semi-synthetic diets with either mostly unsaturated fatty acids (82%) or less unsaturated fatty acids (58%) for one year while monitoring the fatty acid composition of their fat. In addition, at four times throughout the year we offered captive vireos choices between three diets that differed only in fatty acid composition to determine whether their dietary preferences changed seasonally. Vireos fed the 82%U diet had fat stores comprised of mostly (77%) unsaturated fatty acids, and vireos fed the 58% U diet had fat stores comprised of less (66%) unsaturated fatty acids. Regardless of season, red-eyed vireos consistently preferred diets with long-chain unsaturated fatty acids (18:1) over diets with long-chain saturated fatty acids (18:0, 16:0). Evidence for selective metabolism of fatty acids in vireos included: (a) their ability to preferentially store 16:0 as indicated by its proportion in the diet (10.9%) compared to that in the depot fat of vireos (24.9%); (b) a gradual increase from 11% to 22% in the proportion of 18:2n6 in the fat of vireos while they were fed a diet with 28% 18:2n6 for > 1 year. Selective metabolism plays an important role in determining the fatty composition of body fat in vireos and other birds, although fatty acid composition of diet more strongly influenced fatty composition of our captive vireos.