Energy acquisition and storage are important for survival and fecundity of birds during resource-limited periods such as spring migration. Plasma-lipid metabolites (i.e. triglyceride [TRIG], β-hydroxybutyrate [BOHB]) have been used to index changes in lipid stores and, thus, have utility for assessing foraging habitat quality during migration. However, such an index may be affected by energetic maintenance costs, diet, and other factors, and further validation under experimental conditions is needed to understand potential sources of variation and verify existing indices. We evaluated a plasma-lipid metabolite index using 30 female and 28 male wild Lesser Scaup (Aythya affinis; hereafter scaup) held in short-term captivity (~24 hr) during spring migration. Similar to previous observational studies, BOHB was negatively associated and TRIG was positively associated with mass change (R2 = 0.68). BOHB estimates were nearly identical to those published on free-living scaup, but TRIG estimates differed from free-living scaup and varied by sex, with females having a greater rate of predicted mass change than captive and free-living males. Our results suggest TRIG may be a better measure of energy income than deposition because lipid deposition likely varies with energetic maintenance costs, stress, and underlying physiological processes while TRIG relates primarily to energy income. In contrast, BOHB was a reliable predictor of negative mass change across sexes. The sex-based differences in apparent lipid deposition rates warrant further research before a generalizable model is advisable for comparing mass change predictions across studies. However, if predictions are standardized, this technique is generally robust to variations in energy income vs. lipid deposition across sexes. Accordingly, our evaluation provides verification for the utility of plasma-lipid metabolites as an indicator of foraging habitat quality during migration.

中文翻译：

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血浆代谢物指数对外部变化具有稳健性，并且是小穗中觅食栖息地质量的有用指标

在资源有限的时期，如春季迁徙，能量获取和储存对于鸟类的生存和繁殖力非常重要。血浆脂质代谢物（即甘油三酯 [TRIG]、β-羟基丁酸酯 [BOHB]）已被用于指示脂质储存的变化，因此可用于评估迁徙期间的觅食栖息地质量。然而，这样的指数可能会受到能量维持成本、饮食和其他因素的影响，需要在实验条件下进一步验证，以了解潜在的变异来源并验证现有指数。我们使用春季迁徙期间短期圈养（约 24 小时）的 30 只雌性和 28 只雄性野生小 Scaup（Aythya affinis；以下简称 scaup）评估了血浆脂质代谢物指数。与之前的观察性研究类似，BOHB 呈负相关，TRIG 与质量变化呈正相关（R2 = 0.68）。BOHB 的估计与自由生活的 scaup 上发表的几乎相同，但 TRIG 的估计与自由生活的 scaup 不同，并且因性别而异，女性的预测质量变化率高于圈养和自由生活的男性。我们的研究结果表明，TRIG 可能比沉积更好地衡量能量收入，因为脂质沉积可能随能量维持成本、压力和潜在的生理过程而变化，而 TRIG 主要与能量收入相关。相比之下，BOHB 是跨性别负质量变化的可靠预测因子。表观脂质沉积率的基于性别的差异值得进一步研究，然后才建议使用可推广的模型来比较研究中的质量变化预测。然而，如果预测是标准化的，那么这种技术通常对不同性别的能量收入与脂质沉积的变化是稳健的。因此，我们的评估验证了血浆脂质代谢物作为迁移期间觅食栖息地质量指标的效用。