Cooperative prey herding by the pelagic dolphin, Stenella longirostris

Sonar techniques were used to quantitatively observe foraging predators and their prey simultaneously in three dimensions. Spinner dolphins foraged at night in highly coordinated groups of 16-28 individuals using strict four-dimensional patterns to increase prey density by up to 200 times. Herding exploited the prey's own avoidance behavior to achieve food densities not observed otherwise. Pairs of dolphins then took turns feeding within the aggregation that was created. Using a proxy estimate of feeding success, it is estimated that each dolphin working in concert has more access to prey than it would if feeding individually, despite the costs of participating in the group maneuvers, supporting the cooperation hypothesis. Evidence of a prey density threshold for feeding suggests that feedback from the environment may be enough to favor the evolution of cooperation. The remarkable degree of coordination shown by foraging spinner dolphins, the very strict geometry, tight timing, and orderly turn taking, indicates the advantage conferred by this strategy and the constraints placed upon it. The consistent appearance of this behavior suggests that it may be a critical strategy for energy acquisition by spinner dolphins in energy poor featureless environments in the tropical Pacific Ocean.