For top consumers in marine environments, trophic discrimination factors (∆¹³C and ∆¹⁵N) between food and consumers’ tissues are expected to be similar among related species. However, few studies conducted in the laboratory indicate a large variability among species, which should be potentially higher in free-ranging animals. Here, we test for differences in tissue-specific ∆¹³C and ∆¹⁵N values of two wild penguin species (Chinstrap Pygoscelis antarctica and Gentoo P. papua) breeding in sympatry at Livingston Island, Antarctica. A total of 41 adults and 28 chicks, and food items comprised exclusively by Antarctic krill (Euphausia superba, n = 22) in Chinstraps and almost exclusively in Gentoos, were sampled for stable isotope analyses. Overall, Δ¹³C values varied between -1.8 and 4.0 ‰ and Δ¹⁵N values ranged from 1.2 to 6.1 ‰, and these differed between species, tissues and age-classes. Δ¹³C in adult penguins differed between species for feather and blood. Species-specific differences in Δ¹³C and Δ¹⁵N were seen in chick nail and muscle, while only Δ¹³C values differed between species in feathers. Our results show that trophic discrimination factors can differ substantially between closely related species consuming similar prey, especially in Δ¹³C value. Variation in Δ¹³C was driven by species, tissue and age-class, while variation in Δ¹⁵N was mostly driven by tissue type. Trophic discrimination factors may be associated to physiological and/or stress factors which may fluctuate in the wild, and this was particularly evident on chicks. This study highlights the use of diet-specialised species for the determination of trophic discrimination factors in the wild.

对于海洋环境中的顶级消费者，食物和消费者组织之间的营养鉴别因子（Δ ¹³ C 和 Δ ¹⁵ N）预计在相关物种之间相似。然而，实验室中进行的研究很少表明物种之间存在很大的变异性，自由放养动物的变异性可能更高。在这里，我们测试了在南极利文斯顿岛同区繁殖的两种野生企鹅物种（Chinstrap Pygoscelis antarctica和 Gentoo P. papua）的组织特异性 Δ ¹³ C 和 Δ ¹⁵ N 值的差异。总共 41 只成虫和 28 只小鸡，以及仅由南极磷虾（Euphausia superba，n = 22) 在 Chinstraps 中，几乎完全在 Gentoos 中，被采样用于稳定同位素分析。总体而言，Δ ¹³ C 值在 -1.8 到 4.0 ‰ 之间变化，Δ ¹⁵ N 值在 1.2 到 6.1 ‰ 之间变化，这些值因物种、组织和年龄等级而异。成年企鹅的Δ ¹³ C 因羽毛和血液而异。在鸡爪和肌肉中观察到 Δ ¹³ C 和Δ ¹⁵ N 的物种特异性差异，而羽毛中只有 Δ ¹³ C 值在物种之间存在差异。我们的结果表明，在食用相似猎物的密切相关物种之间，营养歧视因素可能存在很大差异，尤其是在 Δ ¹³ C 值方面。Δ ^{13 的}变化C 受物种、组织和年龄等级驱动，而 Δ ¹⁵ N 的变化主要受组织类型驱动。营养歧视因素可能与生理和/或应激因素有关，这些因素可能在野外波动，这在小鸡身上尤为明显。这项研究强调了使用饮食专门物种来确定野外营养歧视因素。