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提供关键洞见，有助于理解环境动态变化以及人类活动对自然资源的影响。 传统食性采样方法往往具有侵入性，或存在采样偏倚，因此开发适用于多物种类群的非侵入性、无偏倚采样方法至关重要。 本研究借助数码摄影技术，针对一种携饵海鸟的雏鸟食性展开调查，并以大凤头燕鸥（Thalasseus bergii）为研究对象，将本研究提出的摄影采样法（photo-sampling）与传统反刍物采样法（regurgitations）进行对比。 在三个繁殖季内，本研究共鉴定出超24000个猎物个体，涵盖至少48个不同物种类群，使该种群燕鸥已知的猎物物种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，其测量准确度小于1毫米，精密度约为0.5毫米。 与两处繁殖地的反刍物采样法相比，摄影采样法得到的猎物组成与体型估算结果相近，且物种累积速率更快。 两名研究人员同时开展摄影采样所得到的猎物组成结果同样具有较高一致性。 摄影采样法为携饵鸟类的食性组成与猎物体型调查提供了一种非侵入性、精准高效的研究工具。该方法可降低基于观察者偏差的研究中存在的偏倚，且操作简便易行。鉴于当前对自然生态系统环境变化与人为影响评估的需求日益增长，本研究方法可为生态保护与资源管理决策制定提供全新的技术支撑。