Every autumn and winter, thousands of starlings pack close together and swirl across the sky in one of the natural calendar’s most dramatic spectacles.

But scientists still do not know why the species perform these unique displays and, on Friday, they will call on the British public to help them solve the mystery of why murmurations form, how long they last and why they end.

It is also hoped the Society of Biology’s starling murmuration survey could provide information to help stem the decline of the species, which have fallen 66% in number since the mid-1970s.

Dr Anne Goodenough from the University of Gloucestershire, who is leading the project, said that although experts do not know for certain the reason behind the aerial displays, several theories have been aired.

“Probably the biggest theory is the idea of safety in numbers – it’s an anti-predator strategy. They are vulnerable to aerial predators, things like peregrine falcons and short-eared owls, when they’re in flight.

“If you’ve got quite a big, swirling flock of birds, that creates a mesmerising sight. And that in itself – that movement, that motion – creates a situation where predators are actually confused and then can’t focus on any one individual bird to pick out and predate,” she said.

One possible reason is that the birds flock together to keep warm. “If the thermal theory has any relevance, a bigger flock means you’re likely to have a higher temperature than within a smaller flock. That’s been shown with emperor penguins.”

Another is that the the birds are coming together to share information on roosting sites. “If you’ve got lots of birds coming and dropping into an area, that’s likely to be a good place to roost, so it’s a self-fulfilling prophecy,” she said.

The biggest theory for why the birds flock is safety in numbers. Photograph: Christopher Thomond/The Guardian

But ultimately, Goodenough said, not enough scientific research has been undertaken on murmurations and too much observation of them has been anecdotal. Where studies have taken place, they have tended to focus on two or three murmuration sites. “What we’re really trying to do is harness people power and see what’s going on in the country as a whole.”

The citizen science science survey will ask members of the public to track when murmurations occur, where, what the weather is like, what the temperature is, how long they last and what the birds do at the end of the congregations.

Understanding where and when murmurations occur, Goodenough said, would be useful information to help stop starlings’ decline and better protect them. “There are some sites in the UK that are known as murmuration sites but there must be literally hundreds if not thousands of other sites that support starling murmurations.”