Mesmerising spectacle in the sky
A murmuration of starlings flows across the winter sky as thousands of birds gather to roost at dusk
At the onset of dusk, as the January sky begins to dim, individual starlings rise up from the ground. Soon, small groups of a dozen or so begin to form, then, a flock of 50, followed by another. A larger one, with perhaps two or three hundred birds in all, begins to fill the air. They fly in loose flocks, each beating its wings regularly to keep up with the others. The starlings are gathering to roost. They arrive from all points of the compass, having been out in the fields and coastal marshes all day, feeding on soil invertebrates. Within minutes, the winter skies are covered with countless birds: vast flocks, comprising some 1,000 starlings, cluster more tightly, in close formation. At this moment, the only sounds to be heard are the excited cries of eager spectators, for the starlings do not call until they have finally landed. But as one flock passes directly overhead, and the air flows through their wings, a soft, almost inaudible shushing sound reaches the ears of the watching crowds. The term murmuration is used to describe the aerial displays performed by flocks of starlings gathering to roost, specifically referring to the unusual sound made by the beating of their collective wings. Now, large crowds regularly congregate early on winter evenings to watch this magnificent spectacle of nature.
Safety in numbers
A winter gathering of starlings is undoubtedly one of the greatest British wildlife events to witness, not least because it is so easily accessible. Those who wish to see it do not need to travel to far-flung places, as many roosts are found in well-populated urban areas. Others, including the biggest of all on the Somerset Levels, which can hold up to half a million birds, are within easy reach of rural locations. Roosts can be found in a variety of natural, semi-natural and manmade locations, including woods, reed beds, cliff sides, piers and buildings; in fact, anywhere the starlings can safely gather and perch for the night. The roosts and their dramatic associated displays take place during the winter months for a number of reasons.
The first is that during the spring and summer, starlings, like other songbirds, pair up and hold a territory, so will not gather in large flocks. The second reason is that roosting communally and staying close to fellow birds during cold weather can help prevent heat loss. Finally, most starlings seen in these murmurations are not native breeding birds, but immigrants from Russia and Eastern Europe. They travel westwards in autumn to avoid the bitter winters and find a more reliable supply of food, boosting the UK’s starling population, sometimes by several million. There are other good reasons for starlings to spend the night together. Predators, from foxes to cats and sparrowhawks to peregrines, can easily pick off a lone bird, but in the flock, there is safety. By gathering together, each bird can dramatically reduce its chances of being eaten.
Method in movement
None of this quite explains, however, why starlings often perform spectacular aerobatic displays before they finally go to roost for the night. They do not always do so: on cold, windy nights, they may head straight into the roost site without any aerial acrobatics. But on a good night, for 20 minutes or more, they may swirl around, forming extraordinary amoeba-like shapes against the setting sun. One theory to explain these displays is that each bird is waiting for its neighbours to choose where and when to descend. This is a tricky decision: those that land first may get the choice of the best roost site, but if the others then decide to move elsewhere, they could be left out on a limb and more vulnerable to attack. Conversely, if they leave it too late, they will be forced to jostle for position in the roost itself. If all the perching places are taken, they may even have to move to a new roosting area. So the starlings play an avian version of musical chairs, each closely watching its neighbours as they flow around the sky, waiting for the key move. If a bird of prey, such as a merlin, peregrine or sparrowhawk, attacks at this time, each starling will try to head away from the attacker and towards a safe place in the centre of the flock. This can create mesmerising movements as the flock appears to turn into a living creature, pulsing like a beating heart. The strategy seems to be effective. Predators are often so confused by the mass movement, they are unable to target any individual bird, and so move on. In these vast gatherings, it seems impossible that the starlings can avoid crashing into one another, and yet they do not. The latest theory, suggested by Italian scientists observing the murmurations over Rome, is that each bird
keeps a close eye on its immediate neighbours and simply follows their movements like a formation flyer. When its companions turn, it turns, and so on. The split-second delay between the movement of one and the response of another creates these fluid patterns, just as shoals of fish are observed moving underwater.
Living together
At some point, usually around dusk, the starlings will at last begin to come down to land. On the Avalon Marshes in Somerset, where the starlings roost in vast reed beds, each bird tries to choose the best perch. This is ideally fairly high up on the reed stem so that they do not get covered in their colleagues’ droppings. There is a clear pecking order, with mature males at the top and young females at the bottom. Elsewhere in the country, where the roost is in trees, on a manmade structure or on seaside piers, they huddle up alongside each other, in order to keep warm. As soon as the starlings land, they begin to call. This is a very noisy affair which sounds as though they are telling one another where they have been that day and whether or not they have found enough food. They are indeed communicating, but not so directly. Each starling takes the opportunity to judge the fitness of the other birds around it; searching for the healthiest, best-fed individuals. The next morning, they will follow them to the best areas to feed. Although most people will arrive before dusk to watch the starlings gather, the spectacle is also impressive at dawn. Approximately half an hour before sunrise, the starlings awake and begin to call to one another in a mounting crescendo of sound. Then, as if responding to an unseen signal, the first birds will rise into the air and begin to head off. Soon, a vast stream of birds heads away from the roost. At this time of day, they do not perform their aerobatic antics, as they need to take advantage of the short hours of winter daylight to feed.
“I cannot take possession of the sky, Mount with a thoughtless impulse and wheel there One of a mighty multitude, whose way And motion is a harmony and dance” William Wordsworth, Home at Grasmere