GPS tracks and behaviour detection of chick-rearing streaked shearwaters at Funakoshi Oshima Island, Japan, 2018 & 2019

The study of seabird behaviour has largely relied on animal-borne tags to gather information, requiring interpretation to estimate at-sea behaviours. Details of shallow-diving birds' foraging are less known than deep-diving species due to difficulty in identifying shallow dives from biologging devices. Development of smaller video loggers allow a direct view of these birds' behaviours, at the cost of short battery life. However, recordings from video loggers combined with relatively low power usage accelerometers give a means to develop a reliable foraging detection method. Combined video and acceleration loggers were attached to streaked shearwaters in Funakoshi-Ohshima Island (39'N,141'59''E) during the breeding season in 2018. Video recordings were classified into behaviours and a detection method was generated from the acceleration signals. Two foraging behaviours, surface seizing and foraging dives, are reported with video recordings. Surface seizing was comprised of successive take-offs and landings (mean duration 0.6 and 1.5s, respectively), while foraging dives were shallow subsurface dives (1.9s mean duration) from the air and water surface. Birds were observed foraging close to marine predators, including dolphins and large fish. Foraging detections were validated against video recordings (surface seizing true positive 78%, false positive 5%, foraging dive true positive 66%, false positive <1%). The detection method was implemented to data from longer duration acceleration and GPS datasets collected during the 2018 and 2019 breeding seasons. Foraging trips lasted between 1-8 days, with birds performing on average 16 surface seizing events and 43 foraging dives per day, comprising <1% of daily activity, while transit and rest took up 55% and 39%, respectively. This foraging detection method can address the difficulties of recording shallow-diving foraging behaviour and provides a means to measure activity budgets across shallow diving seabird species.海鸟行为研究长期以来主要依赖于动物搭载标记装置采集数据，需通过解读分析以推定其海上活动行为。相较于深潜海鸟物种，浅潜海鸟的觅食细节研究较少，原因在于难以通过生物记录设备（biologging devices）识别浅潜行为。小型化视频记录仪（video loggers）的研发使得直接观测这类海鸟的行为成为可能，但弊端是电池续航时长较短。不过，将视频记录仪记录数据与低功耗加速度计（accelerometers）相结合，为开发可靠的觅食检测方法提供了可行路径。2018年繁殖季，研究人员在船诘大岛（39°N，141°59′E）为短尾剪水鹱（Streaked Shearwater）佩戴了视频-加速度复合记录仪。研究人员对视频记录的行为进行分类，并基于加速度信号构建了觅食检测方法。通过视频记录，本文明确了两种觅食行为：海面捕食（surface seizing）与觅食潜水（foraging dives）。海面捕食行为由连续的起飞与降落动作组成（平均时长分别为0.6秒与1.5秒）；而觅食潜水则是从空中或水面发起的浅水下潜行为，平均时长为1.9秒。研究观察到，短尾剪水鹱会在包括海豚与大型鱼类在内的海洋捕食者附近觅食。研究以视频记录为金标准对觅食检测方法进行了验证：海面捕食的真阳性率为78%，假阳性率为5%；觅食潜水的真阳性率为66%，假阳性率低于1%。该检测方法已被应用于2018年与2019年繁殖季采集的更长时长的加速度与GPS（全球定位系统）数据集。觅食行程的持续时长为1至8天，短尾剪水鹱日均完成16次海面捕食事件与43次觅食潜水，此类觅食行为仅占每日活动时长的1%以下；而巡游与休息分别占每日活动总时长的55%与39%。本研究提出的觅食检测方法可解决浅潜海鸟觅食行为记录的难题，为测算浅潜海鸟类群的活动预算提供了可靠途径。