Little is known about the dietary richness and variation of generalist insectivorous species, including birds, due primarily to difficulties in prey identification. Using faecal metabarcoding we provide the most comprehensive analysis of a passerine's diet to date, identifying the relative magnitudes of biogeographic, habitat and temporal trends in the richness and turnover in diet of Cyanistes caeruleus (blue tit) along a 39-site, 2° latitudinal transect in Scotland. Faecal samples were collected in 2014-15 from adult birds roosting in nestboxes prior to nest building. DNA was extracted from 793 samples and we amplified COI and 16S minibarcodes. We identified 432 molecular operational taxonomic units (MOTUs) that correspond to putative dietary items. Most dietary items were rare, with Lepidoptera being the most abundant and taxon-rich prey order. We present a statistical approach for estimation of gradients and inter-sample variation in taxonomic richness and turnover using a generalised linear mixed model. We discuss the merits of this approach over existing tools and present methods for model-based estimation of repeatability, taxon richness and Jaccard indices. We find that dietary richness increases significantly as spring advances, but changes little with elevation, latitude or local tree composition. In comparison, dietary composition exhibits significant turnover along temporal and spatial gradients and among sites. Our study shows the promise of faecal metabarcoding for inferring the macroecology of food webs, but we also highlight the challenge posed by contamination and make recommendations of laboratory and statistical practices to minimise its impact on inference.

中文翻译：

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繁殖前森林雀形ine日粮的丰富度和周转率的梯度：一种应用于粪便元条形码数据的混合模型方法。

对食虫性物种（包括鸟类）的饮食丰富性和变异性知之甚少，这主要是由于难以识别猎物。我们使用粪便元条形码技术对迄今为止的雀形目鸟的饮食进行了最全面的分析，确定了沿39个站点，纬度为2°的蓝藻（蓝雀）饮食的生物地理学，栖息地和时间趋势的相对幅度在苏格兰横断面。在2014-15年从筑巢前在巢箱中栖息的成年鸟类收集粪便样品。从793个样品中提取了DNA，我们扩增了COI和16S minicodes。我们确定了432个与假定饮食项目相对应的分子操作分类单位（MOTU）。大多数饮食都很少见，鳞翅目是数量最多，分类单元最丰富的猎物。我们提出了一种统计方法，用于使用广义线性混合模型估算分类学丰富度和营业额中的梯度和样本间变化。我们讨论了这种方法相对于现有工具的优点，以及用于基于模型的可重复性，分类单元丰富度和Jaccard指数估计的方法的优点。我们发现，随着春天的前进，饮食的丰富性显着增加，但随着海拔，纬度或当地树木的组成而变化不大。相比之下，饮食组成沿时间和空间梯度以及站点间表现出显着的周转率。我们的研究表明，粪便元条形码有望推断食物网的宏观生态，