Birdsong is no echo of the past

I LED a dawn chorus outing last weekend. The venue was a forest with exotic trees and shrubs under the cliffs on the hill of Howth.

There’s a large dolmen there. I told the assembled group that the builders who hauled the huge stones into place 4,000 ago, had awakened to the sounds we were hearing that morning. But had they? The bird community has changed over the millennia. There were no magpies, pheasants or collared doves in Ireland long ago. Mistle thrushes, reed warblers and siskins may also be recent arrivals, so some of today’s most vocal birds would not have been around. The drumming of great spotted woodpeckers, the calls of large birds of prey, and even the loud clucking of capercaillies, could have been familiar to the dolmen builders.

Our garden bird species frequented the fringes of woodland long ago but are their songs the same as those of their ancestors? The language the dolmen builders spoke would be incomprehensible to us. Is the same true of bird “languages”? Are avian musical scores fixed and immutable like great classical masterpieces? Or is birdsong more like jazz, with performers improvising continually, allowing the music to change and evolve with the generations?

Some bird songs are fairly stereotyped. The cuckoo’s two notes seem to be the same everywhere; ones I heard in Mongolia sounded just like the cuckoos at home. By the time his chick hatches, the absent father cuckoo has stopped singing. The youngster never hears the song, so it must be hardwired into his brain. Even so, variation is possible. There are normally between 10 and 20 continuous repetitions of the two-note phrase, but some cuckoos go on longer. Up to 300 have been recorded. The tempo and pitch can vary; some birds seem anxious and agitated while others are more laid back. Three-note versions occur and there can even be changes in the “tune”.

Cuckoos sing tonally; their notes come from the diatonic scale on which human music is based. The musical interval is the minor third, but intervals from the second to the sixth are sometimes used.

So, were the cuckoo sounds of long ago necessarily the same as those of today? A manuscript from Reading Abbey contains the words and music of a song written around the year 1260. The Reading Rota opens with the words “Summer is a coming in, loud sings cuckoo”. There’s a repeated refrain with the words “sing cuckoo, sing cuckoo” but no minor thirds accompany it. This seems odd; if the bird sounded as it does today, the temptation to mimic it would have been great. It’s clear, from the name “cuckoo”, that it had a two-note call back then, but can we be sure that the interval between the notes was the same as it is today?

Unlike the cuckoo’s, the songs of most birds are learned rather than inherited. A baby chaffinch, while still in the nest, hears his father and the neighbouring males singing. In the autumn, the youngster feebly mimics the song he has heard. Come the spring, this “plastic sub-song” reappears and the young male begins to develop his own unique version of the full-blown form with its distinctive flourishes. In the case of a chaffinch, though not all birds, the same song will be used by him throughout his life.

During the 1950’s and 60’s WH Thorpe, a Cambridge biology professor, raised chaffinch chicks in soundproof boxes. In due course the birds, which had not heard others singing, produced bland songs of a similar length to that of normal chaffinches but unrecognisable as such. Young birds, therefore, have a basic song template hardwired into their brains to which form and syntax are added by listening to, and imitating, older singers. But the learning component of birdsong is evident even without Thorpe’s experiments. Chaffinch songs vary geographically, with local accents and dialects recognisable even to humans. This is also true of wrens and many American species.

The dawn choruses heard by the dolmen builders were probably quite different from those of today. What a pity we can’t hear one.