Assessing the applicability of stable isotope analysis to determine the contribution of landfills to vultures’ diet

Human activities cause changes to occur in the environment that affect resource availability for wildlife. The increase in the human population of cities has led to a rise in the amount of waste deposited in landfills, installations that have become a new food resource for both pest and threatened species such as vultures. In this study we used stable isotope analysis (SIA) and conventional identification of food remains from Egyptian Vultures (Neophron percnopterus) to assess the applicability of SIA as a new tool for determining the composition of the diets of vultures, a group of avian scavengers that is threatened worldwide. We focused on an expanding Egyptian Vulture population in NE Iberian Peninsula to determine the part played by landfills and livestock in the diet of these species, and aimed to reduce the biases associated with conventional ways of identifying food remains. We compared proportions of diet composition obtained with isotope mixing models and conventional analysis for five main prey. The greatest agreement between the two methods was in the categories ‘landfills’ and ‘birds’ and the greatest differences between the results from the two methods were in the categories ‘livestock’, ‘carnivores’ and ‘wild herbivores’. Despite uncertainty associated to SIA, our results showed that stable isotope analysis can help to distinguish between animals that rely on waste and so present enriched levels of δ 13C than those that feed on the countryside. Indeed, a high proportion of food derived from landfills (nearly 50%) was detected in some breeding pairs. Furthermore we performed GLMM analyses that showed that high values of δ 13C in Egyptian Vulture feathers (a proxy of feeding in landfills) are related with high levels of humanization of territories. This method has the potential to be applied to other threatened vulture species for which there is a lack of information regarding resources they are consuming, being especially important as the main causes of vultures decline worldwide are related to the consumption and availability of food resources.

人类活动会引发环境变化，进而影响野生动物的资源可获得性。城市人口增长导致填埋垃圾的总量不断增加，这类设施已成为有害生物与受威胁物种（如秃鹫）的新型食物来源。本研究通过稳定同位素分析（Stable Isotope Analysis, SIA）与传统的埃及秃鹫（Neophron percnopterus）食物残骸鉴定方法，评估将SIA作为确定全球受威胁食腐鸟类——秃鹫饮食组成的新型工具的可行性。本研究聚焦伊比利亚半岛东北部持续扩张的埃及秃鹫种群，以明确垃圾填埋场与家畜在该物种种群饮食中所占的份额，并旨在降低传统食物残骸鉴定方法所带来的偏差。我们针对五大主要猎物类别，对比了同位素混合模型与传统分析方法得出的饮食组成占比。两种方法的结果在“垃圾填埋场”与“鸟类”类别中一致性最高，而在“家畜”“食肉动物”以及“野生草食动物”类别中差异最大。尽管稳定同位素分析存在一定不确定性，但本研究结果显示，该方法可有效区分依赖垃圾食物的个体与依赖乡村自然食物的个体：前者的δ¹³C水平显著高于后者。事实上，部分繁殖配对的个体中，有近50%的食物来源于垃圾填埋场。此外，我们开展了广义线性混合模型（Generalized Linear Mixed Model, GLMM）分析，结果显示，埃及秃鹫羽毛中的高δ¹³C值（可作为其在垃圾填埋场觅食的替代指标）与领地的高人类化程度显著相关。鉴于全球秃鹫种群衰退的主要诱因与食物资源的获取及可获得性密切相关，该方法有望推广应用于其他缺乏食物消耗相关数据的受威胁秃鹫物种，具有重要的应用价值。