Homing Ability of Adélie Penguins Investigated with Displacement Experiments and Bio-Logging

Adelie Penguins Pygoscelis adeliae live exclusively in Antarctica and commute between the sea for foraging and the land for breeding. During these movements, they must navigate various environments: underwater, on sea ice and on land; an unusual set of challenges among animals. Navigation mechanisms of this species were intensively studied about 50 years ago, but technological limitation at that time made it hard to fully understand movement patterns under experimental as well as natural conditions. Recent developments in animal-borne data loggers have enabled us to record movement paths and activities of such birds. In this paper, we report the results of displacement experiments combined with bio-logging on Adelie Penguins, conducted for the first time since initial experiments more than 50 years ago. Two chick rearing birds were caught at their nests and data loggers with GPS and accelerometers were deployed on their backs. The birds were artificially displaced and released approximately 1 km from the breeding colony. From the release point, their options to return to the nest were either walking over land or swimming in the sea. The birds successfully returned to the colony 6.0 h and 8.1 h after release, taking 44 min and 41 min, respectively, from the onset of homeward movement. Both individuals took what appeared to be the straightest and shortest course crossing over land. They spent most of the homing phase (51.2% and 66.2%) walking and only entered the water – in the same place – in the last stretch homewards. The results of our study demonstrate the homing ability of Adelie Penguins from a distant location after artificial displacement and the potential use of positional and acceleration data to study the navigation of penguins that travel by both land and sea.