Starlings congregate in communal roosts throughout the winter, numbering from a few thousand to over a million birds. The leading hypothesis for why they gather in such huge numbers is that it is an anti-predator strategy.
By diluting the risk as the group size increases, the chance of any one individual suffering predation decreases and many eyes means that vigilance increases with the number of individuals.
Most aerial predators (sparrowhawk, peregrine falcon for example) hunt by targeting a single bird. The confusion caused by the constant movement may hinder their ability to lock onto an individual.
[Birds of a feather flock together: Insights into starling murmuration behaviour revealed using citizen science - A. Goodenough et al 2017. PLOS ONE]
Read more about my work on starling murmurations in my latest photo essay.
Into the Darkness. A sparrowhawk makes a foray into the swirling mass of starlings, returning moments later with a bird in its talons.Smoke screen. Sometimes the flock is so large that it fills the horizon like a curtain of smoke. As they pass overhead, the sky darkens and the sound of thousands of wingbeats fills the air.Perspective. Stretching to the horizon, these displays are visible for miles, likely acting as a beacon to signal the roost location.Untitled 11. After a day’s dispersed feedings, small flocks funnel into progressively larger ones along flight lines to the 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.Cyclone. The flock turns as it undulates above the wetland.Funnel. The flock swirls, twists and turns, forming shapes like funnels and tornadoes as the birds seek a suitable spot to land.Ebb and Flow. The flock is strangely peaceful in its immensity as it ebbs and flows like a tide over a mile of wetlands.Untitled 7. The starlings confuse aerial predators by forming dense twisting shapes, ensuring the safety of the group.Untitled 8. The starlings confuse aerial predators by forming dense twisting shapes, ensuring the safety of the group.Untitled 9. As darkness descends, the vast flock concentrates over the chosen roost site and the birds cascade to the ground.Untitled 10. The Danish term for murmuration, “sort sol,” translates to “black sun” evoking the strangeness of the veiled landscape.
