Measurements of the strength of an adult skua and the force required to drag an adelie penguin chick from a colony

How much force was necessary to drag struggling adelie penguin (Pygoscelis adeliae) chicks of different ages from a colony was measured by holding a chick in a harness as they tugged against a spring balance. How strong a skua is was also determined by measuring their strength as they jerked at meat held on the hook of a spring balance. It was found that live chicks could be dragged out with a force equal to about two thirds of their gross weight. Skuas can jerk with a force up to 1600 grams weight and sustain 1300 quite readily. These figures tally well with the forces theoretically needed by skuas to drag out a 2000 gram chicks, about the maximum size they have been seen to haul bodily from a colony.