Why do starlings dance in the sky?

November 8, 2017 - 06:20

Flocks of several hundred thousand starlings can fly swiftly in coordinated and mesmerising formations, even when trying to evade predator birds. Why do they do it, and more significantly, how?

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The National Geographic video above shows a flock of starlings in the Netherlands. How confounding and impressively graceful is this aerial ballet.

“It is one of the great phenomena of nature – a real attraction,” says Svein Dale. He is a professor at the Norwegian University of Life Sciences (NBMU) and researches birds and bird behaviour, and is particularly concerned about threatened species.

Dale has witnessed the starling phenomenon but not the largest flocks of all.

“But I have seen starling flocks probably numbering a few hundred thousand.”

Why and how the starling flies in such beautiful formations – hypnotically dancing in the air and making coordinated split-second turns – is something ornithologists have researched and continue trying to fathom.

Scientists at the University of Warwick conducted a study in 2014 in which they created a computer simulation of starling flocks fleeing a bird of prey.

Their study indicated that the aerial formations made by the birds change constantly to give each bird an optimal view of the surroundings. The simulation can be viewed here:

Another study has shown that the birds act in accordance with the closest seven other starlings as the flock performs its impressively rapid and synchronised acrobatic tricks in the sky.

“I think it can be a combination of both,” says Svein Dale.

Not just because of enemies

Birds, including starlings, mostly fly in flocks as a defence against birds of prey. The more individuals in a flock, the less risk for each bird of being the unlucky one who gets taken out by a hawk or another raptor. But starling flocks also fly in such formations when no predators are around, according to Dale.

“To my understanding, this can occur when the flock is touching down at a place to spend the night. I don’t know whether it has a function at such times or they are just having trouble deciding where to land.”

“One might think there is a risk in being the first bird to touch ground, and there is a little commotion before the flock lands.”

"So this is not a case of birds engaged in an artistic performance?"

“No, starlings are not flying like this to put on a good show for humans,” says Dale with a laugh.

Nor is it certain that the swift turns we see in a large flock of starlings in the sky are experienced so dramatically by the birds themselves.

“It is worth remembering that small birds have reflexes that exceed ours by a long shot. What we experience as an ultra-fast coordination of a flock of starlings is more of an easy tempo for the individual starling,” says Dale.

More common in Norway before

There are many places in Denmark where large flocks of starlings can be observed, and more can be read about them on the web pages of Denmark’s Nature Agency. The Danes call the flocks a “sort sol”, meaning a black sun.

Dale says that lots of photographers congregate in Denmark to capture the flocks on video.

Opportunities to see starling flocks have declined in Norway in the last few decades. The starling populations have suffered setbacks and the bird is now considered to be “near threatened” on the national red list which Dale is currently working on.

“There used to be many places where they could be sighted, especially in late summer. There were large flocks of starlings that landed at overnight spots, such as the lake Østensjøvannet in Oslo,” says Dale.

“Up to 5,000 could be seen in a flock, but several years have passed since any flock has been reported at Østensjøvannet. For decades there have been concerns about declining startling populations in this country and the decline has been steady.”

The number of starlings that nest in Norway has fallen by about 17 percent in ten years, according to figures from 2013. In the same decade, the population of starlings dropped by about 30 percent in Sweden.

“As the starling is one of several species linked to the agricultural landscape which appear to be in a long-term decline, and this same decline is registered in our neighbouring countries, we figure this is part of a general decline,” according to the Norwegian red list, where the starling is classified as “near threatened”.

Fewer birds in Europe

The decrease of starlings can be part of the greater picture, as bird populations have generally been on the decline in Europe.

“Europe has in the main lost vast numbers of birds,” says Svein Dale.

The reduction in the past 30 years has been about 400 million individual birds.

Norwegian starlings tend to winter in Great Britain. But Dale says the general weakening of starling populations could be attributed to poorer access to good wintering areas in Southern Europe.

He thinks this might have also impacted Norwegian birds.

Owners of olive orchards in Southern Europe understandably want their harvests to go to market, rather than feed starlings. They have been known to use some harsh methods to rid themselves of the freeloaders, including attempts to blow up whole colonies with dynamite, according to Dale. 

Starlings are not the only ones

Flying in enormous flocks is not uniquely limited to starlings. The largest bird flocks to nest in Norway are bramblings.

“When they gather to rest at night when spending the winter in Central Europe there can be several million touching down in a single forest area. The record was observed 1951–52, when one flock consisted of 70 million bramblings. In such situations, you can see some of the same flying patterns as when starlings fly,” says Dale.

Most of the starlings in Norway have now left for warmer countries. They majority migrate out in the course of October and they usually return by the end of March. Some spend the winter in Norway, especially along the coast.

In certain European cities further south, like the Italian capital, huge flocks of starlings can still be observed. Neighbourhoods where they choose to rest can be drenched in their droppings. 

One of the steps Roman authorities have taken to put a stop to this spreading of guano, which can even make streets slippery, has been to rent falcons to defend against the onslaught of starlings, according to The Guardian.

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Read the Norwegian version of this article at forskning.no

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Translated by
Glenn Ostling