Behaviour that’s just starling

It’s starling ‘murmuration’ time again. 

The birds with the star-like spots on their shiny black feathers gather each evening into huge flocks over woods and reed beds.

They wheel noisily about the sky in great swirling and pulsating patterns, as parties fly in from all sides to join them. Hundreds of thousands, occasionally over a million, individuals participate in these wildlife spectacles.

As darkness falls, the birds drop suddenly from the sky to spend the night perched shoulder to shoulder on branches or reed-stems.

The ceaseless cacophony of screeches chatters and whistles continue until the light fails, whereupon a great silence descends.

Starlings mimic natural and man-made sounds. It’s even been suggested that a familiar whistling call they produce imitates the sound of bombs falling during World War II. Why do starlings behave like this and how does it benefit a bird to roost with so many others?

Although not popular with the public, these are fascinating and highly successful creatures. Numbers were low in Ireland in the early 19th Century, although 200,000-strong ‘murmurations’ were recorded in Dublin’s Phoenix Park in the 1840s.

Breeding was slow to spread; the species didn’t nest in west Cork and Kerry until the 1950s. Our native ones are sedentary; most of the starlings here in winter are visitors from Northern Europe, some from as far away as Poland. Numbers vary depending on how cold it is abroad.

Small birds usually defend territories, keeping their neighbours away at nesting time, but starlings dislike being on their own and prefer a village lifestyle.

Holes in walls buildings and trees provide nest sites, a few square metres of territory around each one being defended. Nor is the colony just a random association; breeding is synchronised. All females begin laying within a few days of each other.

There’s a price to be paid for communal living. Competition for mates, and places to nest, is high and, with so many mouths to feed, local food sources can be stretched.

Infidelity is widespread; some of the young a father helps raise may not be his own. Females will lay eggs in others’ nests, fooling neighbours into raising the chicks. In some studies, up to half of all clutches were found to be ‘brood parasitized’.

Such behaviour puts pressure on males: the suspicious husband stalks his partner, keeping a watchful eye lest he be cuckolded. She has a more relaxed attitude to infidelity; there’s security, from a genetic point of view, in having some of her eggs fathered by other males.

Most songbirds continue feeding their young when they have left the nest. Not so starlings. Oddly for such a gregarious species, the fledglings become independent within a few days.

The youngsters form juvenile-only flocks, the avian equivalent of teenage gangs, roaming the countryside.

Adults will join them later. Starling expert Chris Feare found that 58% of winter flocks in England had less than 50 birds, 6% had more than 250.

Individuals must compete with the neighbours in the scramble for food but being in a group has advantages; with many eyes and ears to spot danger, the bird in a crowd is much less likely to be taken by a predator.

Indeed, an attacking hawk may become so confused by the swirling mass of flying starlings that it fails to catch any of them.

Roosting close together warms the immediate environment, reducing the risk of hypothermia during cold winter nights. But starlings don’t just form flocks; the local groups merge into giant multitudes. How this benefits the birds isn’t clear.

Can it really be safer to fly 30 or 40km to a roosting site, risking attack by sparrow-hawks and peregrines along the way, than spending the night locally among a few hundred? Is the environment of the larger roost so much warmer that it compensates the birds for the energy used flying to and from it?

What is all the vocalisation and mimicry about? The starling may be a common and slightly despised creature, but it’s a most enigmatic one.


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