Consider a flock of birds: they usually appear to our eyes as an undifferentiated collection of interchangeable individuals. That’s also how they’re treated in computational models of collective behavior—an oversight that’s due for a correction.
“Research on collective behavior typically treats flocking animals as ‘mindless’ agents following identical rules,” write researchers led by Hangjian Ling and Nicholas Oullette, both civil engineers at Stanford University, in the journal Nature Ecology & Evolution. “In reality interactions may be influenced by social relationships among group members.”
Oullette’s lab studies the dynamics of crowds: how, for example, the physics describing runners at a marathon’s starting line also apply to the motion of waves of water. Their latest study was inspired by a paucity of research on the effects of social interactions on flocking dynamics, a subject of interest to both evolutionary biologists and designers of autonomous vehicles.
Using high-speed 3D video, the researchers analyzed the movements of jackdaws, a Eurasian member of the crow family who mates for life and in winter joins large flocks. They found that mated pairs fly close together, their movements more synchronized to one another than the flock as a whole.
Mated pairs also flapped their wings less than unmated birds. It would appear that coordinating one’s motions to a single individual rather than many is energy-efficient. Flocks with more mated pairs tended to move less nimbly than flocks with fewer, however, suggesting that when individuals are attuned to
“Our findings suggest that social bonds have major impacts on the structure and function of flocks,” write the researchers, “and therefore have important cognitive and evolutionary implications.”
Keeping track of specific individuals within a fast-moving collective could be yet another pressure that’s shaped the evolution of cognition in social animals. The dynamics created by these relationships could also influence the evolution of flocking behavior itself.
Oullette’s team hope their findings and similar research on other species could also inform models of collective behavior, and thus the design of interacting autonomous vehicles and aerial drone flocks. Those applications are speculative at present, but at least one implication can already be realized: appreciating that, far from being an undifferentiated group, a flock of birds is a society.
Source: Ling et al. “Costs and benefits of social relationships in the collective motion of bird flocks.” Nature Ecology & Evolution, 2019.
Image: Martyn Fletcher
About the author: Brandon Keim is a freelance journalist specializing in animals, nature and science, and the author of The Eye of the Sandpiper: Stories From the Living World. Connect with him on Twitter, Instagram and Facebook.