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.

食性研究可为觅食行为解析提供关键洞见，对认知环境动态变化及人为活动对自然资源的影响具有重要意义。
传统食性采样方法往往具有侵入性或易产生偏差，因此开发适用于多物种类群的非侵入性、无偏采样方法至关重要。
本研究以大凤头燕鸥（Thalasseus bergii）为研究对象，利用数码摄影技术对其雏鸟的喂食食性展开调查，并将本研究采用的摄影采样法（photo-sampling）与传统的反刍呕吐物采样法（regurgitations）进行了对比。
在三个繁殖季的调查中，本研究共鉴定出超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物种多样性提升了一倍以上。本研究提出了一种基于摄影图像估算主要猎物物种——欧洲鳀（Engraulis encrasicolus）体长的方法，其测量准确度小于1毫米，精密度约为0.5毫米。相较于两个繁殖种群的反刍呕吐物采样结果，摄影采样法得到的猎物组成与体长估算结果与之相近，且物种累积速率更快。此外，两名研究人员同步开展摄影采样所得到的猎物组成结果也具有较高一致性。
摄影采样法为携饵海鸟的食性组成与猎物体长研究提供了一种非侵入性的精准高效工具。该方法可规避基于观察者的研究易产生的偏差，且操作简便。鉴于当前对自然生态系统环境变化与人为影响开展评估的需求日益增长，本研究提出的方法可为保护与管理决策制定提供全新的技术支撑。