Singing ‘chiffchaff’ by numbers

The chiffchaff’s song might be described as simple by the standards of birds. It’s made mainly of two alternating notes—the high-pitched ‘chiff’ and the lower-pitched ‘chaff’—along with the occasional quiet chortle or tweet. Compared to a nightingale or blackbird, it’s not especially exciting. Unless, that is, you’re into spreadsheets.

A diagram of a chiffchaff’s song: green is chiff, red is chaff, yellow is chortle, and blue and purple are different varieties of tweet.

A simple colour-coded transcription of this song, with one column per phrase, reveals an amazing degree of variation. Amongst 124 phrases, 39 are totally unique. Most of that variation comes from the first three notes—specifically, between two chaffs or chortles before the first chiff, or only one, or even, in very rare cases, three. The ends of phrases also contain some curveballs, like the chiff-chiff-chaff-chaff in the third phrase, or the high-pitched tweet towards the middle (in purple) that only happens twice.

These are very small details that you probably wouldn’t notice unless you transcribed the song, but once you do notice them, they become fascinating. Why doesn’t the chiffchaff ever sing chaff-chortle-chaff-chortle? Are those random tweets actually deliberate, or just absent-minded half-chaffs? What happened to make those little two- and three-note phrases so short? Was it startled by a pigeon? Did it forget what it was about to say, like a person who walks into a room and then forgets what they came for?

This is a spring recording, but if you’d passed through a woodland in Ireland, Wales, or northern England more than 60 years ago and heard a chiffchaff’s song, you would have actually have been able to tell it was summer. Until the early 1960s, chiffchaffs migrated south for winter to escape the temperatures that their tiny, nine-gram bodies couldn’t survive.

In the last few decades, though, large numbers of males and about half as many females have stayed to take advantage of the increasingly mild UK winter climate. The volunteer study group at RSPB Rye Meads recorded 58 overwinterers in 2015-16, up from five in 1995-6 and one in 1975-6. The Woodland Trust says that up to 1,000 birds are now thought to spend the whole year in the UK.

What’s not clear yet is how the chiffchaff’s overwinter success is affecting other bird species, although chiffchaffs are hardly aggressive. If you hear one, though, do add a record to the Nature’s Calendar initiative, which helps scientists track the impacts of weather and climate on wildlife. º

25 May 2022


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