BTO: Aerial ballet of starling flocks

It is during these cold winter months that we are treated to the sight of starling flocks and their amazing pre-roost ‘murmurations’.

Vast numbers of birds gather at favoured sites, performing an aerial ballet that ripples and pulsates in a manner that suggests a single organism rather than a gathering of individuals. Each of these flocks has more humble beginnings, as small groups of birds begin to arrive at their evening roosts. These roosts, which may be in a stand of conifers, a reedbed or on a human structure – such as a pier – are often used over many nights, allowing the numbers of birds present to build to staggering proportions.

As the small groups of birds come together and coalesce into a larger flock, so the ballet begins. Individual birds within the flock turn in the air, prompting their neighbours to respond to the movement and creating a ripple that spreads rapidly across the flock.

As the light of evening slips towards night the behaviour of the flock changes and the birds move towards the roost itself. Birds on the bottom edge of the flock plunge towards the roost but often pull away again. It is as if they are testing their nerve, seeing who will take the plunge into the unknown.

The murmurations may signal to other starlings that there is a roost forming, prompting individuals to join the gathering. The flocks also catch the eye of predatory sparrowhawks and peregrines, which quickly learn to exploit the presence of so many individuals. Watching birdwatchers may be treated to the sight of a peregrine, silhouetted against the setting sun, punch a hole through the flock as it attempts to snatch an unwary individual.

There is a sense that both the number of murmuations and the numbers of birds involved have declined over recent years, something that the available evidence seems to support. Our wintering starlings are a mixture of local breeders and winter visitors, the latter arriving from breeding populations located elsewhere within Europe. We know that the numbers wintering here are influenced by the weather conditions elsewhere, and a run of mild winters will have seen more individuals remain on the Continent, rather than cross the Channel to our shores.

Thanks to data from British Trust for Ornithology (BTO)-led surveys we also know that our resident population has undergone a prolonged period of population decline. Our breeding starling population has declined by 89% over the past 45 years, a staggering loss for such a familiar species. It is thought that changes in the way that we manage our pastoral farmland are likely to be one of the main factors driving the decline. Starlings feed on soil-dwelling invertebrates and populations of these have been hit by increasing use of agricultural chemicals. You may have to travel that bit further this winter to witness this wildlife spectacle.

Pictures by Jill Pakenham and John Harding.