Starling flocks preparing to roost are a winter delight

It was a large flock of starlings preparing to settle down for the night and the show they were putting on was truly spectacular.

It was like a thousand black dots in the sky, all acting as one drawing weird and wonderful shapes in the dusk.

One second the flock was a tight ball, which would quickly stretch out into two balls, then morph into the shape of a fish before finally spiralling upwards into a helix.

It is a scene enacted throughout many of our towns and cities every winter's evening, with the flocks - or murmurations as they are sometimes known - of starlings undergoing their early evening aerobatic rituals before bedding down into their roosts in buildings, trees or under bridges.

But how they achieve such aerial synchronicity, acting like one flowing organism rather than hundreds or in some cases thousands of individuals, is a question that has long baffled ornithologists. Now exciting new research has shed some light on the issue.

A study by Italian scientists has suggested that each starling's movement is influenced by a fixed number of other starlings in its proximity, so that turns and changes in speed are quickly transmitted throughout the whole flock.

In other words, every starling is watching a number of its immediate neighbours and copying their movements.

There is no lead bird or group within the murmuration orchestrating the display, but rather it is a decentralised means of control where cohesion and movement is created by the birds interacting en masse.

Winter flocking is probably a means of protection against predators such as the peregrine, with the numerous swirling birds making it hard for a falcon to focus on an individual target. A flock also has many more pairs of eyes to detect the approach of a predator.

One also can't help feeling that there must be some kind of interactive social benefit for starlings to group together in such large numbers. Sadly the spectacular sight of starlings flocking into their winter roosts is a less frequent one compared with the recent past, with the UK breeding population plummeting by 71 per cent between 1970 and 1999.

Initial signs several years ago suggested that the Scottish breeding population was experiencing partial recovery, but this has not been backed-up by the most recent survey data, which indicates a slow decline is underway again. The winter population is augmented by large numbers of immigrants from Scandinavia and Russia, whose numbers have also declined significantly in recent decades.

One winter roost in Dumfries and Galloway held up to half a million birds in 1979 and there are reports of other roosts in Scotland holding as many as a million birds in the late 1960s, although most flocks today are much smaller, comprising perhaps only a few thousand individuals.

It is thought that the decline of the starling in many parts of its European range can be attributed to changes in farming practices, which has led to a loss of suitable permanent pasture, one of the bird's preferred foraging habitats, which in turn has led to a decrease in the abundance of invertebrates such as leatherjackets to feed on.

Despite such falls in numbers, the starling is still a relatively common bird in Scotland. It is, perhaps, all too easy to take our more familiar birds for granted, but the starling really does merit special appreciation.

Take another one of its endearing traits: the starling is a great mimic and likes nothing better than to imitate the calls of other birds. So, the next time you hear the plaintive cry of a curlew ringing through the streets of Edinburgh, Glasgow, or Aberdeen, more likely than not it is a starling doing its star act.

This article was first published in The Scotsman, 1 January, 2011