A robin is singing from the lilac tree. The wistful, doodling song is achingly familiar, yet I realise I haven’t heard it for a while. Not that robins have been absent; I have seen them flicking through the hedge and bouncing across the lawn all summer. But with the avian orchestra at full strength – visiting warblers adding their voices to the tumbling tune of the chaffinch, the seesaw squeak of the great tit and the resonant refrain of the song thrush – the contemplative notes of the sweet little bird in russet coat¹ are easy to miss.

Now that autumn has bustled in, the chorus has hushed and the clean, clear song of the robin rings out, heralding what 19^th-century Irish poet William Allingham called the falling of the year.²

Robins (Erithacus rubecula) sing all year, although their repertoire changes with the seasons. In spring and summer, male birds sing to attract a mate, see off rivals and guard territory. “Females tend to prefer males with more complex and lengthy songs, which are often indicators of genetic quality and overall health,” writes Stephen Moss in The Robin: A Biography. Remember this, because it will be important later. 

After the breeding season, pairs disband and robins of both sexes sing to announce and defend a territory, ideally one with enough food and shelter to see them through winter. Juveniles, newly red-breasted after shedding their mottled brown ‘I’m-no-threat’ plumage, must do the same. Only one in four will make it through their first year. Fittingly, the winter song strikes a more melancholy note.

It has been a year since I moved to the Cairngorms, and I’ve been thinking how birdsong has steered me through the seasons. From the honking of pink-footed geese in winter, to the first chiffchaff in spring, the call of the cuckoo in May and the high-summer screams of swifts, the shifting soundscape has helped root me in place.

Everyone should be able to tune into nature’s soundtrack, but as the world grows louder, it is in grave danger of being drowned out. In Europe, one in five people are exposed to harmful levels of noise pollution: the clamour of construction work, the drone of machinery, roads and railways, airports and industry. 

The din may be ours, but we are not the only ones who suffer. Anthropogenic noise is considered a global threat to other species, affecting communication, behaviour, health and breeding success.

In cities, incessant background noise can mask up to 30 percent of bird vocalisations. To be heard, birds must adapt.

“Yelling louder is one solution to communication in noisy environments,” writes David George Haskell in Sounds Wild and Broken: Sonic Marvels, Evolution’s Creativity, and the Crisis of Sensory Extinction. Research from the Max Planck Institute for Ornithology found that some urban birds – even the diminutive wren – sing up to 10 decibels louder than their rural counterparts. 

As for robins, a study from the University of Leicester found that city-dwelling birds use longer, simpler phrases with fewer syllables than their country cousins. They also abandon the lower reaches of their repertoire, to avoid having to compete with the low-frequency hum of towns and cities. This narrows their vocal bandwidth, like an orchestra’s string section being restricted to the violins.

Robins are not the only birds to change their tune in noisy environments. City great tits belt out their teacher, teacher song in shorter and more hurried phrases. Wrens hold their notes longer; blackbirds sing higher.

Rising earlier is another tactic: in many clamorous cities, the dawn chorus begins before the roar of rush-hour traffic. One robin in Sheffield took to singing only at night to avoid a daytime noise level equal to the relentless whine of a vacuum cleaner.

Birds’ ability to adjust their communication in the face of environmental noise is remarkable, but not without cost. Sacrificing complexity for audibility can change how a bird is perceived. Lower-frequency sounds are often indicators of fitness and body size, so discarding those low notes risks being underestimated by rivals, or overlooked by potential mates. 

Remember how female robins prefer mates with a decent playlist? A study in 2020 revealed that birds in noisy environments had a more limited repertoire than those in quieter areas, making mate choice harder.

The offspring of those that do breed successfully face their own noise-related challenge. Birds are born with an innate ability to produce song, but how they sing is shaped by listening, to themselves and to others of their species (known, delightfully, as tutor birds). If the songs that these youngsters are exposed to are limited in virtuosity – or if background noise prevents them getting their ear in – they will never become the maestros they might have been.

Whether raising the dial on volume requires more energy remains uncertain. Research on one species, the zebra finch, found that boosting song amplitude by 10 decibels increased energy expenditure by around 16 percent. Other studies contend that it is not the act of singing louder, but the stress hormones triggered by living with constant noise that deplete precious energy reserves. Either way, noise takes its toll: sparrows living in louder places have been found to be less healthy than those in quieter settings.

And we are not so different: chronic noise exposure has been linked to heart disease, high blood pressure, stroke, stress and depression, and contributes to an estimated 16,000 premature deaths in Europe each year. I have to confess a low tolerance for noise. When I lived in a city, I would often jump at sudden clatters and wince at sirens, while those around me barely seemed to notice. The quietude here feels like a gift.

Since I started writing this piece, robins have materialised everywhere – singing for their supper, for shelter, for survival and sometimes, it seems, just for the joy of it.

Spontaneous singing (not related to territory or breeding) triggers the release of opioids in the brain, akin to the happy hormones behind the ‘runner’s high.’ Darwin guessed as much, noting in The Descent of Man that “birds continue singing for their own amusement after the season for courtship is over.” 

I am glad, though not surprised, to learn that birds enjoy singing as much as we enjoy listening. But the orchestra is shrinking. One in eight bird species is now globally threatened with extinction, while breeding bird numbers in the UK have dropped by almost 40 million since the 1960s, when Rachel Carson first warned of a ‘Silent Spring.’ 

That is why, long after my morning coffee is finished, I am still sitting here by the lilac tree, listening, holding on to the robin’s every last note.

Endnotes:

1. From The Autumn Robin by John Clare.
2. From Robin Redbreast by William Allingham.