The Aerial Ballet of Starlings

By Jose Luis Gallego, environmental communicator (@ecogallego)

During the silent grey dusk of a winter’s day, when the last light fades over frosty, dormant fields, the sky offers an unexpectedly lively contrast. Moments before night falls, and in a striking counterpoint to the hushed landscape, enormous flocks of black birds perform one of the most extraordinary aerial displays in all European avifauna: the ballet of the starlings. They only perform this winged dance during the coldest months of the year, from mid-autumn until mid-winter, and it doesn’t coincide with their mating season. 

Starlings in flight at dusk

In the skies over cities and villages, over vineyards, olive groves, and barren fields, tens or hundreds of thousands of starlings come together in distinctive flocks resembling an airy mass of black dots. Seen from afar, they recall clouds of grainy smoke that expand and contract in an apparently perfect choreography without ever colliding with one another.

One bird might decide to swoop low, and the flock follows. Then another pulls the group left; shortly after, the flock suddenly moves up and back to the right. No one knows what inspires or guides this relentless dance. None of the starlings know which pattern they will follow, where they will fly from one moment to the next, yet they all seamlessly conform to the same choreography, resulting in one of the greatest and most celebrated aerial ballets in nature.

So far ornithologists who study this curious behaviour have not been able to identify the specific mechanism that allows the starlings to avoid collisions. Crashing into each other in mid-flight is dangerous: the birds could potentially plummet to the ground and sustain injuries. What is the guiding force that prevents them from doing so? Apparently, sound is one of the most decisive factors.  Flocks of starlings are notoriously loud, and each bird communicates its position to the others by calling out to them. 

A starling perched on a branch

Light seems to play a key role in compelling the birds to make their characteristically sudden collective turns. Each individual eschews the light and the blue of the sky, instead seeking refuge in the darkness of the group. This allows them to move as a homogenous mass, forming a disciplined dance troupe in which each dancer pays close attention to what the others are doing.    

However, what inspires these birds to fly in such large groups is not a passion for art – in this case, dance – but a sense of survival. Together they can elude attacks by one of their most relentless foes: the peregrine falcon.  Faced with such a whirl of possible prey, the raptor can’t focus its attention on a single starling long enough to grab the individual with its sharp talons in mid-flight. Clustered close together, the flock of starlings explodes into thousands of individuals once the falcon approaches, expanding in all directions to then come back together seconds later. This manoeuvre disorients and confuses the bird of prey. As a strategy, it resembles what large shoals of fish do to confound their underwater predators. 

A starling on a tree branch

Spain is home to two of the most populous species of starlings: the common starling (Sturnus vulgaris) and the spotless starling (Sturnus unicolor). The common starling is a medium sized bird, around 20 centimetres in length and weighing about 80 grams. The dense plumage is an iridescent shade of black and very shiny, beautifully speckled in white and gold, making this one of Europe’s most elegant birds. 

It has a short yellow bill and short red legs. Starlings feed on seeds and wild fruit, although in urban settings, it is quite the opportunist, fighting over crumbs with pigeons and sparrows (and more recently, parakeets). It has a characteristic whistling call – powerful and high-pitched – that goes up and down in tone harmoniously.  But that’s not all: starlings are also capable of imitating other birds, and the sounds of church bells and car horns, with astonishing accuracy.  

The spotless starling is almost identical to its common cousin in size, shape, and behaviour, but, as the name suggests, it sports spotless black plumage, without iridescence or speckling. It is not unusual for both species to form mixed flocks, and when we observe them flying together from a distance, it is practically impossible to tell them apart. 

A starling in a leafy tree

The Iberian population of both species combined comes to about four million pairs. During particularly cold winters, however, their migration patterns can bring other European starlings (more than 60 million, with the common starling being the most abundant) to our fields, villages, and cities where they form enormous flocks of tens or even hundreds of thousands of birds.

When night falls, and after dancing across the sky, starlings settle into their sleeping sites, often filling the trees along streets, squares, and in city parks. This can occasionally cause problems with their neighbours, leading to complaints about noise and accumulated excrement.  

The breeding season begins between March and April. Starlings nest in cavities, either in the crevices of buildings or between roof tiles, but also seek out nesting boxes or hollow tree trunks. The eggs are sky blue, and a clutch contains up to half a dozen. Incubation lasts two weeks. The young fledge after 20 days.