Flocks move with remarkable synchrony and order such as this can have radically different origins. It can be the result of a top-down centralised control mechanism - i.e. the presence of one or more leaders. Or, it can arise as bottom-up self-organisation.
How the group behaves under strong predatory pressure provides crucial information about its organisational structure. In a group where all individuals follow a leader, without interacting with each other, there is strong order, as everyone will move in the same direction, yet information transfer is poor. Unless the falcon is detected by the leader, the group will not respond to it.
Instead, flocks are self-organised. When one bird detects a falcon attack it will turn to avoid it. This turn is noticed by its neighbours who also turn. They influence their neighbours, and so on.
[Scale-free correlations in starling flocks - A. Cavagna, G. Parisi et al 2010, PNAS]
Read more about my work on starling murmurations in my latest photo essay.
Out of nowhere. As dusk approaches, groups of starlings arrive in dribs and drabs, coming in to roost after feeding in the fields. Then, as if out of nowhere, thousands of birds appear on the horizon.Dementor II. The starling that turns to avoid a falcon attack is followed by its nearest neighbour — this behaviour ripples through and redirects the entire group.Untitled 4. Birds burst skyward as the final arrivals displace those already settled in the densely packed reeds.The chase. My main aim this winter was to capture some predator-prey interaction. I could see glimpses of the flock being split by the predators but the fast pace and rapid changes of direction made planning my shots difficult.Into the Reeds. The starlings commit en masse for the reed bed, approaching fast and low, swooping into the safety of the vegetation.Pirouette. Small groups of starlings circle above the reeds, performing rapid turns before diving down to roost.Bait ball. Even when the hawks are elsewhere the predators have the starlings on edge and the flock twists and turns as if being pursued. The swirling mass of birds can seem to appear out of nowhere, and just as quickly vanish. The fleeting shapes and patterns are a result of a precise mix of weather, season, food and predation and will never again be repeated.Untitled 5. The starlings whirl in small groups in the fading sunlight of this calm evening—unusual due to the absence of predators.UFO. On this evening, unusual due to the absense of predators, large groups of starlings arrive above the reedbeds, and then, in a swift and orderly way they descend to the safety of the reeds.Meteor. On a gusty November evening, instead of forming a large flock, the starlings arrive in small groups. After a few seconds of rapid twists and turns the whole group plunges into the reeds, safe for the night.Follow the Leader. A small group of starlings appear to lead the way as the entire flock flies overhead.Trails at Dusk. Birds gather in the surrounding trees and trickle in to join the flock as the numbers rise.Untitled 6. Roost sites are mostly rural; here, the starlings have found safety in tall vegetation surrounded by water.Untitled 7. After the first starlings dive into the reeds, thousands of birds quickly follow, raining down to the ground.
