Sato Katsufumi, Daunt Francis, Watanuki Yutaka, Takahashi Akinori, Wanless Sarah
International Coastal Research Center, Ocean Research Institute, The University of Tokyo, Otsuchi, Iwate, Japan.
J Exp Biol. 2008 Jan;211(Pt 1):58-65. doi: 10.1242/jeb.009811.
To understand the foraging strategies of free-ranging diving animals, time series information on both foraging effort and foraging success is essential. Theory suggests that wing stroke frequency for aerial flight should be higher in heavier birds. Based on this premise, we developed a new methodology using animal-borne accelerometers to estimate fine-scale temporal changes in body mass of a pursuit-diving, piscivorous seabird, the European shag, Phalacrocorax aristotelis. We hypothesized that variations in body mass determined from changes in wing stroke frequency before and after a series of dives would be related to the amount of prey captured. The estimated net gain in body mass during a foraging trip was highly variable, ranging from -30 to 260 g, values that were extremely similar to food loads obtained from shags on the Isle of May in previous years using water-offloading and nest balances. Load sizes estimated using the wing stroke method were strongly and positively related to both cumulative flight time and return flight time. At the trip level, load size was unrelated to cumulative dive bout duration and the total amount of time spent underwater. However, highly significant relationships were apparent at the individual bout level, with birds showing bigger mass gains following longer dive bouts. Results from this study are therefore extremely encouraging and suggest that changes in body mass determined from changes in wing stroke frequency may provide a reliable method of obtaining short- to medium-term information on foraging effort and success of diving seabirds.
为了解自由放养的潜水动物的觅食策略，获取觅食努力程度和觅食成功率的时间序列信息至关重要。理论表明，体重较重的鸟类在空中飞行时的翅膀拍击频率应该更高。基于这一前提，我们开发了一种新方法，利用动物携带的加速度计来估计一种追逐潜水的食鱼海鸟——欧洲鸬鹚（Phalacrocorax aristotelis）体重的精细时间变化。我们假设，根据一系列潜水前后翅膀拍击频率的变化所确定的体重变化，将与捕获的猎物数量相关。一次觅食行程中估计的体重净增加量变化很大，范围从 -30 克到 260 克，这些数值与前几年在五月岛使用排水法和巢秤从鸬鹚身上获得的食物负载量极为相似。使用翅膀拍击方法估计的负载量与累计飞行时间和返程飞行时间均呈强烈正相关。在行程层面，负载量与累计潜水回合持续时间以及在水下花费的总时间无关。然而，在个体回合层面，明显存在高度显著的关系，即潜水回合时间越长，鸟类体重增加越大。因此，本研究的结果非常令人鼓舞，表明根据翅膀拍击频率变化确定的体重变化可能提供一种可靠的方法，来获取关于潜水海鸟觅食努力程度和成功率的短期至中期信息。
