Watch video of a starling flock in full flight

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Tourists are flocking to Gretna Green to see one of nature’s most astonishing sights: tens of thousands of starlings swooping for food.

Passing motorists on the nearby A74 have been advised by police to keep their concentration on the road.

Sergeant Scott McLachlan, of Dumfries and Galloway police, said that drivers were slowing down and pulling over on to the hard shoulder to look at the birds. He said: “We want people to enjoy the birds but firstly they need to be safe.

“I would say to drivers that if they want to see the starlings then they should come off the road and not pull over on to the hard shoulder.”

Although starlings are on the “red list” of endangered species, enormous flocks are still seen regularly around the country, with gatherings containing up to seven million birds.

Some of the most popular locations for watching starlings are Brighton Pier, the Somerset Levels and at Glastonbury Tor, where birdlovers gather most evenings during January and February.

A RSPB spokesman said that despite the spectacular displays, the British breeding population of starlings had declined by around 65 per cent in the past 30 years. He said that the birds, including those which migrate from northern Europe to roost in Britain during the winter months, will soon separate into smaller groups as they prepare to breed.

He said: “Starling roosts are found in locations where large numbers of birds can gather in safety. But these sites are becoming scarcer, and roost sizes are declining as the numbers of starlings Europe-wide decline.”

He said that there would be few opportunities left this year to witness vast, swirling flocks of starling because by the beginning of March the birds would be dispersing.

Recent research has unravelled part of the mystery of how the birds manage to create such complex patterns while flying. Starlings in Flight, a pan-European group of physicists, biologists and economists, last month explained the principles: each bird focuses on seven of its neighbours and, as the flock turns and wheels around, it responds to the movements of these particular individuals.

No matter how far these birds are driven apart, they will gradually move back towards each other. The findings contradict the widely held belief that each starling simply watches the bird immediately in front.

The scientists discovered this by studying starlings swarming over Rome’s main railway station, then creating complex 3-D computer models to analyse the behaviour of individual birds.

Iain Thompson, an observer at Gretna Green, said: “I just happened to look up at the sky and I could see it turning from blue to grey to black.

“It really makes you marvel at the natural world. How can so many birds come together all at once? It’s almost apocalyptic.”

The RSPB spokesman said: “They are a very sociable bird all year round and will congregate together when not in the breeding season.

“Partly it’s a defence mechanism because there is safety in numbers — it’s like fish going into great big shoals. It is more difficult for a predator to pick one off. The flocks are more likely to be seen at dawn and dusk because that’s when they are going out looking for food.”

Birds of a feather

— The starling, Sturnus vulgaris, is a noisy, gregarious bird. During summer they live in small, loose groups but they join communal nighttime roosts in winter

— The groups can number several thousand birds and spend the day feeding in smaller flocks

— Their flight is fast and direct and they walk and run confidently on the ground

— It is estimated that there are 804,000 pairs breeding annually in Britain

— Although they remain one of the most common garden birds, the British breeding population is now red-listed, and starling numbers are declining across much of Europe, with fewer birds migrating to Britain over the past few years

— By February, our resident birds gradually start to move back to their breeding areas and soon after the others will start their migration back north

— To attract a mate, the male builds the base of the nest from dry grass and leaves in a hole and sings from perches close to the nest entrance. The female completes the nest by making a nest cup and lining it with fine grasses, moss and feathers

— Starlings usually lay four to six eggs in mid-April. All birds within a colony start to lay eggs within a few days. The female does the majority of the incubation

— Their main predator is the domestic cat

Source: RSPB

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