Starlings are not everyone’s favourites, especially in the USA, but I like them. They are gregarious birds, and while in the summer they live in small loose groups, during the winter months they join thousands of others into communal night time roosts, which can number several thousand birds, and then spend the day feeding in smaller flocks. The sudden disappearance of the starlings in the winter is caused by summer roosting sites becoming unavailable which forces them to relocate, resulting in the temporary abandonment of some feeding areas.
In the wintertime, both resident and immigrant birds form large roosts, gathering in buildings, trees or reed beds. The roosts often number several thousand, but those that gather in reed beds, for example in Norfolk, can number over a million birds. As the day draws to a close, the Starlings return to the roost and before settling down for the night the increasingly large flock darkens the skies as it swirls around making patterns in the sky. Although not in these great numbers I have seen several large flocks close to where I live and a starling flock like this is called a murmuration, a word that perfectly describes the rustle of thousands of pairs of wings.
Starling murmurations are one of the most dazzling displays in the natural world, as a flock continually changes shape like a sort of monchrome kaleidoscope. The movement of the flock is a brilliant piece of choreograph and ornithologists have discovered that to be a member of a flock individual birds have to learn three simple rules: Steer to avoid crowding local flockmates (separation), steer towards the average heading of local flockmates (alignment) and steer to move toward the average position of local flockmates (cohesion). This is called the flocking algorithm and was first worked out in 1986 and subsequently became important in the world of computer graphics and is used extensively in both developing games and making movies.
These huge winter gatherings are boosted by thousands of birds that come to Britain’s milder Atlantic climate to escape the harsh cold of the European continent, especially from Scandinavia and Russia. There are several reasons to get together in the way they do, safety in numbers of course, information exchange (if some come back from a good feeding area others may learn of it) and warmth at night through roosting closely together. The birds feed up to twenty miles away from their winter roost but return each evening for company.
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