Omega-3 long-chain polyunsaturated fatty acids support aerial insectivore performance more than food quantity

Abstract

<p id="d10576159e198">Insect abundance is an important predictor of survival and performance for many taxa of aerial insectivores, which forage on a mixture of aquatic and terrestrial insects that differ in fatty acid composition, particularly omega-3 long-chain polyunsaturated fatty acid (LCPUFA) content. We raised Tree Swallow ( <i>Tachycineta bicolor</i>) chicks on either a high or low quantity of feed with either high amounts of the LCPUFA found in aquatic insects or an equivalent amount of the precursor omega-3 PUFA, alpha-linolenic acid, but low LCPUFA. LCPUFA content was more important for Tree Swallow chick performance than food quantity. Tree Swallows may be timing breeding to coincide with the peak abundance of high-LCPUFA aquatic insects. </p><p class="first" id="d10576159e204">Once-abundant aerial insectivores, such as the Tree Swallow ( <i>Tachycineta bicolor</i>), have declined steadily in the past several decades, making it imperative to understand all aspects of their ecology. Aerial insectivores forage on a mixture of aquatic and terrestrial insects that differ in fatty acid composition, specifically long-chain omega-3 polyunsaturated fatty acid (LCPUFA) content. Aquatic insects contain high levels of both LCPUFA and their precursor omega-3 PUFA, alpha-linolenic acid (ALA), whereas terrestrial insects contain much lower levels of both. We manipulated both the quantity and quality of food for Tree Swallow chicks in a full factorial design. Diets were either high-LCPUFA or low in LCPUFA but high in ALA, allowing us to separate the effects of direct LCPUFA in diet from the ability of Tree Swallows to convert their precursor, ALA, into LCPUFA. We found that fatty acid composition was more important for Tree Swallow chick performance than food quantity. On high-LCPUFA diets, chicks grew faster, were in better condition, and had greater immunocompetence and lower basal metabolic rates compared with chicks on both low LCPUFA diets. Increasing the quantity of high-LCPUFA diets resulted in improvements to all metrics of performance while increasing the quantity of low-LCPUFA diets only resulted in greater immunocompetence and lower metabolic rates. Chicks preferentially retained LCPUFA in brain and muscle when both food quantity and LCPUFA were limited. Our work suggests that fatty acid composition is an important dimension of aerial insectivore nutritional ecology and reinforces the importance of high-quality aquatic habitat for these declining birds. </p>