King penguins excel at swimming. With such short legs, walking is not their forte and drains a lot of energy. Yet, every summer king penguins come ashore and trek inland to breed. They can’t forage during that time, so they pack on the pounds before coming ashore and then fast while on land.
To determine how the extra weight affects a penguin’s waddle, biologist Astrid Willener and her colleagues captured 10 wild male king penguins as they came ashore on Possession Island, between Madagascar and Antarctica. Special monitors called accelerometers measured aspects of the penguins’ gait while the animals walked on treadmills before and after a fasting period.
Fat birds were less steady on their feet than thin birds, the team reports February 17 in PLOS ONE. King penguins carry this weight on their front, which likely shifts their center of gravity and results in a less stable posture.
Penguins that are too wobbly could be vulnerable. If king penguins can't stand up and walk, they will be spotted by their predators such as giant petrels and eaten, says Willener. “So it is a huge matter for them to be able to still walk steady while being ‘fat’.”
Researchers trained king penguins, like this mid-weight bird, to walk at normal speeds on treadmills.