Data from: Dietary studies in birds: testing a non-invasive method using digital photography in seabirds

Dietary studies give vital insights into foraging behaviour, with implications for understanding changing environmental conditions and the anthropogenic impacts on natural resources. Traditional diet sampling methods may be invasive or subject to biases, so developing non-invasive and unbiased methods applicable to a diversity of species is essential.
We used digital photography to investigate the diet fed to chicks of a prey-carrying seabird and compared our approach (photo-sampling) to a traditional method (regurgitations) for the greater crested tern Thalasseus bergii.
Over three breeding seasons, we identified >24 000 prey items of at least 48 different species, more than doubling the known diversity of prey taken by this population of terns. We present a method to estimate the length of the main prey species (anchovy Engraulis encrasicolus) from photographs, with an accuracy <1 mm and precision ~ 0·5 mm. Compared to regurgitations at two colonies, photo-sampling produced similar estimates of prey composition and size, at a faster species accumulation rate. The prey compositions collected by two researchers photo-sampling concurrently were also similar.
Photo-sampling offers a non-invasive tool to accurately and efficiently investigate the diet composition and prey size of prey-carrying birds. It reduces biases associated with observer-based studies and is simple to use. This methodology provides a novel tool to aid conservation and management decision-making in the light of the growing need to assess environmental and anthropogenic change in natural ecosystems.

饮食生态学研究可为觅食行为研究提供关键见解，对理解环境变化以及人类活动对自然资源的影响具有重要意义。传统的饮食采样方法往往具有侵入性或易产生偏差，因此开发适用于多种类群的非侵入性、无偏差采样方法至关重要。
我们以携带猎物的海鸟——大凤头燕鸥（Thalasseus bergii）的雏鸟日粮为研究对象，采用数码摄影技术开展调查，并将照片采样法（photo-sampling）与传统的反刍采样法（regurgitations）进行了对比。
在三个繁殖季内，我们共鉴定出超过24000个猎物个体，涵盖至少48个不同物种，使该种群燕鸥已知的猎物种类多样性提升了一倍以上。我们开发了一种基于照片估算主要猎物物种——欧洲鳀（Engraulis encrasicolus）体长的方法，其测量准确度优于1毫米，精密度约为0.5毫米。与两个繁殖群的反刍采样法结果相比，照片采样法得到的猎物组成与体型估算结果高度一致，且物种积累速率更快。此外，两名研究人员同时开展照片采样所得到的猎物组成结果也无显著差异。
照片采样法作为一种非侵入性工具，可精准高效地开展携带猎物鸟类的日粮组成与猎物体型研究。该方法能够降低基于观察者的研究中易出现的偏差，且操作简便。鉴于当前对自然生态系统环境变化与人类活动影响开展评估的需求日益增长，本方法可为自然保护与管理决策提供全新的技术支撑。