Bird Michael I, Tait Elaine, Wurster Christopher M, Furness Robert W
School of Geography and Geosciences, University of St Andrews, St Andrews KY16 9AL, Scotland, UK.
Rapid Commun Mass Spectrom. 2008 Nov;22(21):3393-400. doi: 10.1002/rcm.3739.
We report results obtained using a new technique developed to measure the stable-isotope composition of uric acid isolated from bird excreta (guano). Results from a diet-switch feeding trial using zebra finches suggest that the delta(13)C of uric acid in the guano equilibrates with the diet of the bird within 3 days of a change in diet, while the equilibration time for delta(15)N may be longer. The average carbon isotope discrimination between uric acid and food before the diet switch was +0.34 +/- 1 per thousand (1sigma) while after the diet switch this increased slightly to +0.83 +/- 0.7 per thousand (1sigma). Nitrogen isotope discrimination was +1.3 +/- 0.3 per thousand (1sigma) and +0.3 +/- 0.3 per thousand (1sigma) before and after the diet switch; however, it is possible that the nitrogen isotope values did not fully equilibrate with diet switch over the course of the experiment. Analyses of other chemical fractions of the guano (organic residue after uric acid extraction and non-uric acid organics solubilised during extraction) suggest a total range of up to 3 per thousand for both delta(13)C and delta(15)N values in individual components of a single bulk guano sample. The analysis of natural samples from a range of terrestrial and marine species demonstrates that the technique yields isotopic compositions consistent with the known diets of the birds. The results from natural samples further demonstrate that multiple samples from the same species collected from the same location yield similar results, while different species from the same location exhibit a range of isotopic compositions indicative of different dietary preferences. Given that many samples of guano can be rapidly collected without any requirement to capture specimens for invasive sampling, the stable-isotope analysis of uric acid offers a new, simple and potentially powerful tool for studying avian ecology and metabolism.
我们报告了使用一种新开发的技术所获得的结果，该技术用于测量从鸟类排泄物（鸟粪）中分离出的尿酸的稳定同位素组成。使用斑胸草雀进行的饮食转换喂养试验结果表明，鸟粪中尿酸的δ(13)C在饮食改变后的3天内与鸟类的饮食达到平衡，而δ(15)N的平衡时间可能更长。饮食转换前尿酸与食物之间的平均碳同位素分馏为+0.34±1‰（1σ），而饮食转换后略有增加，至+0.83±0.7‰（1σ）。饮食转换前后氮同位素分馏分别为+1.3±0.3‰（1σ）和+0.3±0.3‰（1σ）；然而，在实验过程中，氮同位素值可能并未完全随饮食转换而达到平衡。对鸟粪其他化学成分（尿酸提取后的有机残留物和提取过程中溶解的非尿酸有机物）的分析表明，单个鸟粪样本中各成分的δ(13)C和δ(15)N值的总范围高达3‰。对一系列陆地和海洋物种的天然样本分析表明，该技术得出的同位素组成与鸟类已知饮食一致。天然样本的结果进一步表明，从同一地点采集的同一物种的多个样本产生相似结果，而同一地点的不同物种表现出一系列同位素组成，表明其饮食偏好不同。鉴于可以快速收集许多鸟粪样本，而无需捕获标本进行侵入性采样，尿酸的稳定同位素分析为研究鸟类生态和代谢提供了一种新的、简单且可能强大的工具。
