High speed video studies of the spectacular synchronised movements of starling flocks have confirmed that ‘waves’ that ripple through these huge aggregations of birds (seen here in an unrelated video) are an effective anti-predator response.

Despite suspicions that waves in bird flocks are triggered by attacks, Andrea Procaccini, of the Torino Polytechnic, and colleagues note that little systematic work has been done on the issue.

In Animal Behaviour, the team report their analysis of starling (Sturnus vulgaris) flocks under attack from peregrine falcons (Falco peregrinus). Not only do waves in the starling flocks start from the spots where falcons attack, but these waves were also associated with increased success in starlings avoiding being eaten by the falcons.

“The fact that the wave initiation is near the source of an attack is known for bird flocks – although not explicitly called waves – and fish schools only under simulated attack,” write the authors. “Here, we have characterized this phenomenon under true predation.”

They suggest that these wave events likely only occur in birds where the perturbation – from the huge falcon swooping in – is large enough that starling nearly hit each other. The subsequent rapid changes in density, distance and speed of starlings should baffle attackers enough to improve the starlings’ chances of escape.