Jackdaw mobs: From chaos to order

Jackdaw
© iStock/Philartphace

Researchers have observed that jackdaws present chaotic mob behaviour but appear to become more organised when more birds join in.

In order to drive away predators, jackdaws form mobs that are initially disordered. However, new research by the University of Exeter, UK, Simon Fraser University, Canada, and Stanford University, USA, shows a dramatic switch to ‘ordered motion’ once the group reaches a certain density.

The study revealed that jackdaws follow different rules when mobbing predators than when flying to winter roosts. “Traditionally, it is thought that flocking – and other collective behaviour like swarms, fish schools and human crowds – occurs when each individual follows an identical set of rules to every other in the group,” said Dr Alex Thornton, of the Centre for Ecology and Conservation on Exeter’s Penryn Campus in Cornwall.

“This study shows that these rules are actually flexible…When flying to their winter roosts, jackdaws follow what we call ‘topological rules’ – meaning that they respond to the movements of a fixed number of neighbours, and groups remain ordered regardless of how many birds are flying together.

“When mobbing a predator, however, the jackdaws instead use ‘metric rules’ where they respond to all the neighbours that are within a given distance. Here, we see order emerging from chaos.

“Jackdaws issue an alarm call to draw other birds to the mob, and at first these groups are completely disordered.

“Then, when the density of birds reaches a certain threshold, it suddenly flips into an ordered, cohesive state where the birds are aligned with their neighbours and move together in an organised way.

“This sudden transition from disorder to order is similar to the phase transitions we see in physics, like when water turns to ice.”

This study used high-speed cameras to film flocks of wild jackdaws at sites in Cornwall, UK, in order to create 3D reconstructions of the movements of each bird in the flock.

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