Look up on a fall or winter day in the Northern Hemisphere and you can see the fast, synchronous cloud of thousands of birds swirling over their perches. While migrating south, the starlings rest for a few weeks and murmur together in the evening, sometimes lasting up to 45 minutes at a time.
The most common explanation is that the murmurs are a defense against predators. But these massive flocks can also attract predators, making the phenomenon a scientific mystery.
Peregrine falcons, the most common predators of starlings in North America, cause the most elaborate murmurs. A common hunting strategy is to attack the herd once, suddenly and from a distance.
Simulation of a murmur
The flock’s escape maneuvers create complex, overlapping patterns that rapidly change in density and shape. Each escape pattern depends on the threat level and the pattern that preceded it. (Learn more about what we know about starling murmurs.)
Wave events, in which birds create rolling motions through the air, confuse the attacker. The darkest pulse seen during a wave event reflects a change in the orientation of the starlings’ bodies, rather than an increase in density.
There is no leader in a murmuring: the herd behaves as a single entity. To stay together through the different escape patterns, each bird tracks 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 dividing in two, all while staying together.
Starlings’ peripheral vision helps monitor other members of the flock and look for predators.
The falcon surprise attack produces the best results, especially if it succeeds in forcing a bird away from the flock. Although stragglers are relatively rare, predators are much better at catching this single bird 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; Melanie Haiken; Shannon Butler et al. Social birds copy each other’s side scans while monitoring groupmates with low acuity vision. Animal behavior