Foraging behaviour of King Penguins (Aptenodytes patagonicus) in relation to predictable mesoscale oceanographic features in the Polar Front Zone to the north of South Georgia
Marine predators are thought to utilise oceanic features adjusting their foraging strategy in a scale-dependent manner. Thus, they are thought to dynamically alter their foraging behaviour in response to environmental conditions encountered. In this study, we examined the foraging behaviour of King Penguins (Aptenodytes patagonicus) breeding at South Georgia in relation to predictable and stable oceanographic features. We studied penguins during their long post-laying foraging trips during December 2005 and January 2006. For this investigation, we undertook a simultaneous analysis of ARGOS satellite-tracking data and Mk 7 Wild Life Computers Time Depth Recorder (TDR) dive data. To investigate correlations between foraging behaviour and oceanographic conditions, we used SST data from January 2006 from MODIS satellite AQUA. To determine changes in search effort, first passage time (FPT) was calculated; for analysis of dive behaviour, we used several dive parameters that are thought to be reliable indicators of changes in foraging behaviour. King Penguins appeared to target predictable mesoscale features in the Polar Front Zone (PFZ), either a warm-core eddy in the PFZ or regions of strong temperature gradients at oceanic fronts. Two different trip types could be distinguished: direct trips with a straight path to one foraging area at the edge of an eddy or at a thermal front, and circular trips where birds foraged along strong thermal gradients at the northern limit of the PFZ. It is likely that both trip types were a direct consequence of prey encounter rates and distributions, both of which are likely to be associated with these oceanographic features. Circular trips often included passages across the centre of an eddy where birds made deep foraging dives, but remained only a short time in the eddy, possibly because prey were too deep. All birds showed Area Restricted Search (ARS) at scales of <10 km. The two trip types had different ARS patterns, with clear ARS hotspots for direct trips and several ARS hotspots over the whole duration of the trip for circular trips. Dive behaviour had clear relationships with the changing water temperature and the time of day, presumably in response to different prey distribution. Especially for direct trips, dive behaviour showed significant differences within and outside of ARS hotspots. Thus, King Penguins appear to target predictable mesoscale features in the PFZ. They use ARS in different patterns to exploit the environment and adjust their foraging strategy and diving behaviour depending upon conditions they encountered. Diving behaviour showed correlations to ARS patterns, especially for direct trips, which may represent a favourable foraging strategy. The presence of predictable oceanic features allows King Penguins to focus their foraging effort, presumably allowing them to increase their foraging success and decrease their diving effort. (C) 2010 Elsevier Ltd. All rights reserved.
Authors: Scheffer, Annette, Trathan, Phil, Collins, Martin