TWITTER TRENDS

To mark International Dawn Chorus Day this month, we ask: do urban birds sing from the same song sheet as their country cousins?

Has the urban British bird changed its tune?

At the bottom of the alley that runs behind our terrace is a pathless, polleny wilderness of native weeds and garden exotics on the run. It’s impenetrable to human beings, though going by the flattened channel through the metrehigh nettles, and the giveaway pong, it’s clearly no barrier to foxes. Beyond the nettles, there’s a shapeless agglomeration of holly, crab apple, ivy and flowering currant, all growing against some dilapidated garages that they seem to be simultaneously supporting and wrestling to the ground.

Somewhere within this thicket is Sparrow Central, the neighbourhood headquarters from which the birds quest in all directions for food. An incessant cheeping emerges from this tangled estate even when the birds are hunkered down in bad weather, but during April I noticed that if a sparrow had something particularly important to say, it would leave the vegetation and fly up to the guttering of one of the nearby houses.

I soon realised that these birds were probably prospecting for nest sites, and it occurred to me that they flew up there so that their territorial boasts would be amplified by the plaster and brick of the house-fronts. So loud was some of the chirping in the trafficless street that it bounced back in an echo, which, having nowhere else to go, was funnelled up the terrace. The result was that a sparrow broadcasting from the guttering of no. 2 sounded almost as loud at no. 44.

TURNING UP THE VOLUME

Keen interest breeds expertise, and birds are so invested in their singing that it makes sense for them to be highly attentive to their sonic environment. What is for us the niche interest of musicians and sound engineers is for songbirds a matter of life and death. But while sound engineers can control almost every aspect of the studio environment, birds must work with what they find. For thousands of years, birds’ sonic contexts must have altered very little, but that all changed in the past few centuries, as humans began transforming the natural environment into the built environment. A growing amount of research demonstrates that urban birds sing differently in response to the sonic properties of their man-made habitat. Partly this is to do with volume. Normally, this town, like any other, is dominated by motor traffic and other human noise – so the birds need to sing more loudly to be heard. A country robin receiving a visit from a townie cousin would probably find himself having to retreat a twig’s length so as not to be deafened. Some urban nightingales, too, apparently reach such a volume that they breach European Union directives on sound pollution.

But it isn’t only traffic noise that obliges birds to change how they sing: pitch is also important. The rumble and drone of engines occupies the lower frequencies of the sound spectrum, effectively forcing birds to sing higher if they want their voices to carry. Perhaps one reason why wood pigeons are seldom found in city centres is that they can’t hear each other; so they restrict themselves to leafier suburbs where their smoky baritones are more effective. Feral pigeons coo at a slightly higher pitch, but they also tend to be more sociable than their woodland relatives, meaning that they can communicate within the flock without the need to project their voices very far.

Pigeons are in any case fairly monotone, but species whose songs range across a variety of pitches are faced with the slightly

different problem that only part of their repertoire might be properly audible, no matter how they exert themselves to sing louder. This issue is particularly acute for species such as the great tit, whose females seem to have a bit of a thing for deepvoiced males. What’s a male great tit to do, when his winning low notes are obscured by the revving of cars and buses? Clearly, some sort of compromise is required, and while it’s likely that the birds switch to higher registers in noisier parts of town in order to be heard at all, the females’ selective predilection for deeper voices may remain a decisive influence where traffic is lighter.

But as in the case of our terrace sparrows, not only traffic but also the urban landscape itself plays a part in how and where birds sing. Compare a zone of urban space with an acre of woodland. A healthy woodland is a multistorey chaos of trunks, branches, twigs and leaves. These objects all absorb sound and, being of different shapes and densities, they also baffle, cushion and deflect it to variable degrees and in more or less unpredictable directions under the effects of natural growth and the action of the weather.

In contrast, the city plot is dominated by straight lines and reflective surfaces from which birdsong redounds in ways that the bird can come to know. This sonic environment may well provide another incentive for birds to sing at a higher pitch, since a higher note produces fewer echoes to impinge on the clarity of the succeeding one. All these factors might be at work in the mind of the sparrow at no. 2, and more besides. This house is on the street corner, so he is projecting his chirps in three directions at once. Not only that, but it also seems reasonable to assume that the guttering itself has an amplifying effect, for what is a gutter to a proprietorial sparrow if not a prodigious megaphone for the purpose of projecting his voice?

SINGING IN THE SPOTLIGHT

Years ago, when I lived in London, I would lie awake listening to a pair of robins that sang late into the night, long after the last of the other birds had turned in. The song-post of the closer robin was on the scabbed bough of a plane tree, a great brawling thing, like a docker’s arm, that was illuminated throughout the night by a cone of dirty yellowish light beamed down from a corner streetlamp. Meanwhile, his interlocutor sang from a sapling outside a takeaway whose neon sign lit up the upper branches strongly enough to throw a lattice of shadows down on to the trunk. Why were these birds up so late?

Most songbirds are stimulated to sing by changes in the level of light, hence the famous ‘dawn chorus’. The presence of artificial light at their song-posts might have incited these robins to sing, but it doesn’t necessarily explain why they chose to carry on crooning instead of retiring to roost. However, if we subscribe to the thesis that most birdsong is territorial in intention, then it might certainly make sense for robins, and other songbirds such as nightingales, to sing at night. The air is often calmer after dark, enabling birdsong to travel further, and in built-up areas there’s less traffic, too. Town robins do continue singing later than their rural counterparts, and it may simply be that unmated urban robins, or those still to fix a territory, are unable to make themselves heard during the day, whether figuratively because of the competition they face from established males, or literally because their voices are lost in the traffic. These less fortunate birds may then sense that they need to continue singing after dark, but this surely comes at the cost of less time for sleeping and feeding. It may be that in the capitalist update of the nursery rhyme, cock robin is killed by the exhaustion of mandatory overtime.

In the end, as with many aspects of birdsong, after considering local specifics and attending to the birds at first hand, the best we can probably do is rank our explanations in order of plausibility and then admit that we don’t yet know enough. The motivation of the neondoused robins that sang me to sleep in London has not yet been fully explained by science, and though more knowledge would no doubt be a good thing, more whimsical explanations may not be entirely worthless.

EXTRACTED FROM Birdsong in a Time of Silence by Steven Lovatt, published by Penguin Press at £12.99. Copyright © Steven Lovatt 2021.

A COUNTRY ROBIN RECEIVING A VISIT FROM A TOWNIE COUSIN WOULD PROBABLY FIND HIMSELF HAVING TO RETREAT A TWIG’S LENGTH SO AS NOT TO BE DEAFENED