Why do starlings move as a gigantic mass in the sky?

It is, in Patrick Kavanagh’s words, an “apple-ripe September morning”. In the field next door, a handful of swallows, brave in numbers, accost a hovering sparrowhawk high in the sky. I’m hopeful the swallows here will soon disappear and head southwards to the warmth of southern Africa to feed on insects over the winter; in the past few years, disconcertingly, some have chosen not to leave Ireland at all because of our warming climate.
The transition from summer’s vigour to autumn’s withdrawal can feel gradual, but come September 23rd, when day and night are equal in length, the hand of autumn will be everywhere. Already, branches on apple trees in the garden are bent to the ground, weighed down with fruit; on the back wall, spider’s webs stretch across the few remaining berries on the blackberry bush.
A bright green hawthorn shield bug, with 1980s Grace Jones-esque pointed shoulders, crawls across a mouldering tree stump; beside it, on an Irish yew tree planted a few years ago, succulent cup-shaped vermilion “aril” berries have appeared. The birds will devour them.
Happily, the starling season is about to begin. While walking a small back road in Roscommon one evening last week, I heard a rackety chorus of soaring whistles, chirps and clicks from a section of dense hedgerow. It was a bush of starlings. Still chattering, all of a sudden the birds poured out of the hedge and reconvened on a nearby telephone wire, appearing like a string of black pearls on a necklace.
Some three million starlings breed in Ireland every year, and each winter they’re joined by visitors from all over Europe – Sweden, Norway, Denmark, Latvia, Poland and Belgium – who come here for our mild winters. By day, they form small groups and search for food. As the sun falls, they unite into a mass of birds in the sky and fly in unison at up to 80km an hour, shape-shifting like a swirling lava lamp, before descending into the reeds by a lakeshore overnight.
In the past few years, Lough Ennell in Westmeath has become a Mecca for anyone wanting to witness this aerial dance. Local farmer Enda McGuire told me that he once saw a murmuration so large it blocked out the sunset behind. (The Danish word for murmuration – “sort sol” – translates as “black sun”, describing how thousands of starlings can eclipse the sun as they whoosh through the air.)
In the early mornings Enda watches the starlings from his yard as they leave their overnight roosts; they form lines so long it can take 10 minutes for them to pass by.
Reeds by the lakeshore give the starlings shelter, warmth and protection during the night, but a gathering of thousands of small birds in one place will never go unnoticed by predators. On sheep and cattle farmer Padraig Corcoan’s land near Lough Ree in Roscommon, a pair of barn owls nest in an old derelict house. In the early autumn evenings the adult owls perch near the lake and wait for starlings to appear, silently swooping in for the kill.
Starlings will eat most things but favour insects and worms. On frosty days when the ground is impenetrable they’ll go into farmers’ sheds for seeds and livestock meal, whatever they can find.
“They’re not afraid of people; they don’t mind coming into the shed as long as they’re getting fed,” Padraig said. “They’re a right nuisance on that front.”
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Around this time of year their iridescent dark plumage, which shimmers purple and green, becomes freckled with small white astral-shaped spots, forming what poet Mary Oliver describes as “stars in their black feathers”. Starlings never stop jibber-jabbering; they are sponges for new sounds and will mimic what they hear around them – car alarms, other bird species, even human speech.
A few years ago, under the winter’s low-angled light, Padraig and I walked the sodden shores of Lough Ree in the hope a murmuration would bring the evening alive. Knee-high in water, we watched as small groups of starlings appeared from all directions, flying in a line, forming what artist Vincent Sheridan has described as “ropes” in the sky.
We waited for them to unite in the fading light, but the weather was too damp and cold for a murmuration. The birds dissipated into the reeds below.
Why do starlings move as a gigantic mass in the sky like this? To generate warmth during the chilly autumn and winter nights? As a visual invitation for other starlings to join the group? To disorientate predators such as kestrels?
Are they communicating with one another about new feeding areas? And with no leader or hierarchy in the group, how do thousands of birds move together with such astonishing fluidity? Scientists have no definitive answers, and this uncertainty adds an air of frisson to the spectacle.
This autumn and winter, on dark days that can feel interminable, these free evening performances – which continue until February – will mesmerise. It’s definitely not to be missed.