The Listening to Birds Blog

Song Thrush by Nigel Pye

Auditory illusions

Tuesday was a beautiful late winter’s day here in Aberdeen – sunny and quite mild. Quite a few birds were singing and calling and as I walked home through an area of old buildings and warehouses I briefly heard a sound that stopped me in my tracks. It was a drawn out trilling sound, perhaps followed by a few scratchy notes, although it was hard to be certain of this above the noise of the traffic. My immediate reaction was that this was something different, a sound that was not one I normally hear about the city. My next reaction was that it sounded rather like the song of a lesser whitethroat – a sound I know rather well, but one that I would never expect to hear in such a context. The idea that a lesser whitethroat, which is a summer visitor and scarce in Aberdeen at the best of times, would be singing from (it seemed) a rooftop in the middle of February was so implausible that I cast that aside as a possibility. I then remembered that the song of a black redstart is rather reminiscent of a lesser whitethroat. I’m less familiar with this song but I’ve heard it plenty of times on visits to continental Europe where the bird is common. In the circumstances, black redstart seemed more likely, although still unusual; it’s more likely to appear during the winter and they’re quite commonly found in built-up, urban areas. I was willing to entertain the possibility but was that really what I’d heard?

It was clear to me that I needed to hear the sound one more time to be sure of what I was hearing but I waited for a few minutes for the bird to sing again and heard nothing resembling the sound that had made me stop and listen. There were other birds calling, including a few greenfinches which give a few trilling calls but of a rather different quality to a black redstart. Perhaps I’d misheard a greenfinch though. I began to wonder what it was that I hadn’t heard clearly and needed to assess again. Certainly I’d heard the trill – the pattern of the sound – quite clearly. But what about the quality of the sound, the timbre? A black redstart and a greenfinch trill are very different in quality but less so in pattern. Perhaps it was this quality that made it seem different, but I couldn’t be sure from that one brief burst of sound.

So I needed another listen to check the quality of the sound and to do this I needed to be listening properly and giving the sound my full attention. That first time I’d heard it, I’d been listening in an open way rather than focussing on a particular sound. This had only served to draw my attention to something that sounded different, or out of place. The second burst was needed for verification or at least for confirmation that I really was hearing something out of the ordinary. It’s rather like a sequence from a horror film: sound (maybe a snap from a breaking twig or a creaking floorboard) – question (what was that?) – repeat of first sound – confirmation of what the sound is – reaction (run or scream!).

There was no second sound though and yesterday morning I returned to the same area and heard nothing more, although the greenfinches were still there. I suspect I shall be listening a little more attentively as I pass through this area, at least for the next few days. I’ve now begun to wonder what I heard. From such a brief experience I’m struggling to have any kind of memory of what the sound was really like. Perhaps the sound that I now recall is actually one of the recordings of black redstart that I’ve listened back to.

It’s sometimes said that there are no ‘auditory illusions’, only optical illusions. The light does indeed play tricks. But does sound do that too? Certainly sound can be distorted, but I think what’s more significant is the way that we listen to sound and how we go about identifying what it is that we’re hearing. What sort of process do we need to go through in order be sure of what we’re hearing? Birders hear and see lots of ‘possibles and probables’ and doubtless forget about most of them in due course. Most of these fail to become ‘definites’ because of some sort of problem in perception; that second call or prolonged close view that would turn possible into probable and probable into definite never happens. But I think these tantalising episodes are potentially more significant in revealing the processes of perception than any stonewall certainty, satisfying though certainty is.

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