Why do macaroni penguins choose shallow body angles that result in longer descent and ascent durations?

• Published in: Journal of Experimental Biology
• Main Authors: Sato, Katsufumi, Charrassin, Jean-Benoit, Bost, Charles-André, Naito, Yasuhiko
• Other Authors: National Institute of Polar Research Tokyo (NiPR), Laboratoire d'océanographie dynamique et de climatologie (LODYC), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS), Centre d'Études Biologiques de Chizé (CEBC), Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2004
• Subjects: data logger; acceleration; dive; Eudyptes chrysolophus; horizontal transit; gliding; stroke; buoyancy; penguin; [SDE.BE]Environmental Sciences/Biodiversity and Ecology; [SDE.ES]Environmental Sciences/Environment and Society; Kerguelen; Kerguelen Islands; Indian
• Online Access: https://hal.science/hal-00187100; https://doi.org/10.1242/jeb.01265

9 pages International audience It is generally assumed that air-breathing aquatic animals always choose the shortest route to minimize duration for transit between the surface and foraging depth in order to maximize the proportion of time spent foraging. However, empirical data indicate that the body angles of some diving animals are rarely vertical during descent and ascent. Why do they choose shallower body angles that result in longer descent and ascent durations? To investigate this question, we attached acceleration data loggers to eight female macaroni penguins, breeding on the Kerguelen Islands (48°45¢–50°00¢ S, 68°45¢–70°58¢ E; South Indian Ocean), to record depth, two-dimensional acceleration (stroke cycle frequency and body angle) and temperature. We investigated how they controlled body angle and allocated their submerged time. The instrumented females performed multiple dives (N=6952) with a mean dive depth for each bird ranging from 24.5±28.5·m to 56.4±75.1·m. Mean body angles during descent and ascent were not vertical. There was large variation in mean descent and ascent angles for a given dive depth, which, in turn, caused large variation in descent and ascent duration. Body angles were significantly correlated with time spent at the bottomphase of the dive. Birds that spent long periods at the bottom exhibited steep body angles during ascent and subsequent descent. By contrast, they adopted shallow body angles after they had short or no bottom phases. Our results suggest that macaroni penguins stay at the bottom longer after encountering a good prey patch and then travel to the surface at steep body angles. If they do not encounter prey, they discontinue the dive, without staying at the bottom, ascend at shallow body angles and descend at shallow body angles in a subsequent dive. A shallow body angle can increase the horizontal distance covered during a dive, contributing to the move into a more profitable area in the following dive. During the ascent, in particular, macaroni penguins ...