2019 Volume 68 Issue 1 Pages 29-41
At sea behavior of pelagic seabirds can be recorded continuously only by biologging technique. Using the moving speed measured by this technique, on-water/feeding behavior of Procellariiformes that mainly feed on the sea surface can be recorded, but the accuracies have not been determined. To record on-water/feeding behaviour of Black-footed Albatrosses Phoebastria nigripes, we used GPS and acceleration loggers to measure the moving speed, the angle, and the dominant moving cycle of the neck of two individuals that made foraging trips of 213 hr in total from Torishima during their chick brooding period. Accuracies were determined using the still-images taken by the camera loggers at 1–2 min intervals. The proportion of the on-water images (true on-water) categorized as landing on water referring to moving speed was 69–87%, but that referring to acceleration of the neck increased to 100%. Eight of the ten on-water events confirmed with images of potential prey (true feeding), presumably squid, for one bird were categorized also as feeding by referring to acceleration. The accuracy of determination of feeding was unreliable for a second bird, since it indicated only two on-water events with prey images. The duration of on-water bouts with feeding (6.9–16.9 min), determined using acceleration, were longer than those without feeding (3.4–8.0 min). On-water bouts with feeding were often observed during daytime (0.4/h), but some in twilight (0.2/h) and a few during the night (0.1/h). This study shows that landing on water and feeding can be determined using the acceleration of the neck, though the small sample size and the sampling bias of the images (only in daylight) make the conclusions indefinite. Nevertheless, this study indicates that this technique can improve our understanding of the foraging ecology of large surface feeding seabird species.
