Seasonal diet preferences for fatty acids differ between species of migratory passerine, are affected by antioxidant level and relate to the fatty acid composition of wild fruits

Fatty acids are the primary fuel for flight, and play important roles in multiple physiological processes of birds. Birds prefer to eat certain fatty acids over others and these preferences may be related to how efficiently and rapidly certain fatty acids are used as well as the production of reactive oxygen species during fatty acid metabolism. We tested the hypotheses that (1) songbirds prefer certain amounts and ratios of fatty acids, and (2) these fatty acid preferences of songbirds are affected by availability of dietary antioxidants. During fall and spring seasons, we offered European starlings (Sturnis vulgaris) and hermit thrushes (Catharus guttatus), respectively, choices of semi-synthetic diets that mainly differed in three fatty acids (18:1, 18:2, 18:3) and in antioxidant level (low or high vitamin E). We also determined the fatty acid composition of fruits that are commonly eaten by songbirds during migration along the Atlantic coast of New England. We found that starlings increased their consumption of 18:2 and 18:1 when given diets with a higher level of vitamin E compared to diets with a low level of vitamin E. Hermit thrushes consistently consumed a 1:2 ratio of both 18:2 to 18:1 and 18:2 to 18:3 regardless of vitamin E level, and increased consumption of 18:1 when given diets with more vitamin E. We also estimated that hermit thrushes can achieve their preferred ratio of 18:2 to 18:1 in nature by eating a certain combination of wild fruits that are available at stopover sites during migration in southern New England. Our results indicate that birds prefer diets with certain ratios of fatty acids and these preferences change with seasonal physiological needs and dietary antioxidant level. Our findings have important ecological and conservation implications especially concerning the importance of Northern Arrowwood ( Viburnum recognitum) in a bird\u27s diet