Speed consensus and the 'Goldilocks principle' in flocking birds (Columba livia)

The evolution of group living transformed the history of animal life on earth, yielding substantial selective benefits. Yet, without overcoming fundamental challenges such as how to coordinate movements with conspecifics, animals cannot maintain cohesion, and coordination is thus a prerequisite for the evolution of sociality in nonstationary animals. Although it has been considered that animal groups must coordinate the timing and direction of movements, coordinating speed is also essential to prevent the group from splitting. We investigated speed consensus in homing pigeon, Columba livia, flocks using high-resolution GPS. Despite observable differences in average solo speed (which was positively correlated with bird mass) compromises of up to 6% from the preferred solo speed were made to reach consensus in flocks. These results match theory which suggests that groups fly at an intermediate of solo speeds, which suggests speed averaging. By virtue of minimizing extreme compromises, speed averaging can maximize selective benefits across the group, suggesting shared consensus for group speed could be ubiquitous across taxa. Nevertheless, despite group-wide advantages, contemporary flight models have suggested unequal energetic costs in favour of individuals with intermediate body mass/preferred speed (hence the 'Goldilocks principle'). (C) 2019 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.