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.

食谱研究可为觅食行为提供关键洞见，对理解环境变化及人为活动对自然资源的影响具有重要意义。传统的食谱采样方法往往具有侵入性或存在偏倚，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。
我们采用数码摄影技术，对一种携带猎物的海鸟——大凤头燕鸥（Thalasseus bergii）——的雏鸟捕食食谱展开研究，并将本研究的照片采样法（photo-sampling）与传统的反刍食物采样法（regurgitations）进行对比。
在三个繁殖季中，我们共鉴定出24000余件猎物个体，涵盖至少48个不同物种，使该燕鸥种群已知的猎物物种多样性翻倍有余。我们提出了一种基于照片估算主要猎物物种——鳀鱼（Engraulis encrasicolus）——体长的方法，其准确度优于1毫米，精密度约为0.5毫米。相较于两处繁殖地的反刍食物采样法，照片采样法对猎物组成与体型的估算结果与之相近，且物种累积速率更快。两名研究者同步开展照片采样所获得的猎物组成结果也具有较高一致性。
照片采样法为携带猎物的鸟类提供了一种非侵入性工具，可精准高效地研究其食谱组成与猎物体型。该方法可降低基于观察者的研究中存在的偏倚，且操作简便。鉴于当前对自然生态系统的环境变化与人为活动影响开展评估的需求日益增长，本方法为保护与管理决策提供了一种全新的辅助工具。