Moving as a group imposes constraints on the energetic efficiency of movement.

Abstract

Movement is a key part of life for many species. In solitary animals, the energetic costs of movement can be mitigated through energetically efficient strategies that produce faster, straighter movements. However, little is known about whether moving as part of a collective enhances or limits the ability of individual group members to express such strategies. Drawing on 6 years of population-level, high-resolution (1 Hz) GPS tracking of group-living vulturine guineafowl (Acryllium vulturinum), we detected 886 events from 94 tagged individuals where their groups made large, range-shifting displacements in response to changing environmental conditions. We contrasted these movements with data from 94 similarly large displacement events by 19 lone, dispersing individuals. Our results suggest that individuals in groups can significantly reduce their energetic cost of transport when making large displacements (15.3% more efficient relative to their normal daily ranging) by increasing the speed and straightness of their movements. However, even during their most efficient movements, individuals in groups could not achieve or maintain comparable increases in speed to lone individuals, resulting in significantly limited efficiency gains (35.7% less efficient than solitary individuals). Overall, this study provides evidence for a substantial energetic cost arising from collective movement.