Take a look at an autumn or winter day in the northern hemisphere and you may see a fast, synchronous cloud of thousands of birds swirling over their shelters. As they migrate south, starlings rest for weeks at a time and perform a murmur together at dusk, sometimes for up to 45 minutes.
The most common explanation is that murmurs are a defense against predators. But these massive flocks can also attract predators, making the phenomenon a scientific mystery.
Falcon juices, the most common starling predators in North America, cause the most complex murmurs. A common hunting strategy is to attack a flock once, suddenly and from a distance.
Flock escape maneuvers create complex patterns that overlap and change rapidly in density and shape. Each escape pattern depends on the level of threat and the pattern that preceded it. (Learn more about what we know about the murmur of starlings.)
Wave events, in which birds make rolling movements in the air, confuse the attacker. The darker pulse seen during the wave event reflects a change in the way the starling’s body is directed, rather than an increase in density.
There is no leader in the murmur leadership – the flock acts as a single entity. To remain unique through different escape patterns, each bird monitors and mimics the behavior of seven neighbors. Focusing on a fixed number of birds allows the group to adapt quickly, becoming dense or sparse, changing shape or even splitting into two parts – as long as they stay together.
Starling’s peripheral vision helps monitor other flock members and look for predators.
A surprising falcon attack gives the best results, especially if it manages to force the bird to abduct itself from the flock. Although predators are relatively rare, predators hunt this individual much better than a group.
Diana Marques and Kennedy Elliott, NGM staff. Videos: Nick Dunlop. Sources: Charlotte Hemelrijk, University of Groningen; Andrea Cavagna, National Research Council of Italy; Shannon Butler et al. Social birds copy side-shots of each other as they monitor group members of low-sharpness. Animal behavior