The complexity of bird song

At this time of year, we expect the woods to be pretty quiet, with only the rustling of windblown leaves and the occasional chirp of a chickadee or the scolding tirade of a red squirrel. But wait, what is that? Is that bird singing its spring song? By gosh, it is! But why?

For decades I have known many birds sing in September and October. I always presumed the only reason was that the young males are full of hormones and excited to get on with the business of breeding, even though that won’t happen for several months. When the cool days and nights return, we hear snippets of a weak unstructured song or the jumbled notes of a young bird as it tries to mimic ‘dad’ and his beautiful spring song. Sometimes adult males will offer these strange songs in the autumn as well. These songs are often called subsongs and, in some cases, are so distorted it is hard to tell which species is making them as they often mimic parts of other species’ songs.

There is now evidence to show some species start learning their song while still in the egg. It’s kind of like us talking to our unborn child in the womb, so they get used to our voice. Certainly, throughout the nesting cycle, when the little guys are growing up, they hear the male’s song and learn it. Invariably they’re not very good at it. Rest assured, by next spring, when they’ve practiced more on their wintering grounds, they will come back and sing the songs very well!

Sometimes I hear what is called a whisper song. This is a very soft, almost inaudible rendition of their full song uttered by adult birds, usually early in the breeding season. Essentially it is a very soft version of their song, sung from inside the forest canopy and at a very low volume. It is so subtle the birds do not even appear to be singing as the beak is rarely opened as in ‘normal’ song. These are usually given by a sexually mature male in the presence of a female, which may or may not be visible, but rest assured the nest is likely nearby. Whisper songs tend to be precise and repetitive in their basic elements. Simply stated, it is not just a jumble of random notes that may be typical of a subsong; it is an actual albeit quieted song.

Now just in case, you think you have this all figured out, there is one more phenomenon – autumnal recrudescence. This phenomenon derives from the fact that much of the song, birds offer during the breeding season is triggered by hormones, triggered by the number of daylight hours. So picture a cardinal in January starting to sing its song well before we think it should. The song may not be prolonged but is pure and often more evident on bright sunny days. As the late winter and spring progress, the song becomes louder, more frequent and prolonged until it reaches its climax well into the breeding season. In the autumn, we have a period of time when the daylight hours match exactly those of the spring. As a result, we often get males singing simply because their hormones are triggered by the length of the day. At this time, we may get mature males offering their full song for a period of time when breeding success is about zero. Ah, those hormones!

But why don’t birds just sing anytime using their full breeding season song? Many can’t because they don’t know the song yet. Such as young males, or haven’t perfected it yet (late winter males both young and mature), while others await the hormonal triggers that make song viable and necessary.

So I guess the lesson here is that song may occur almost anytime of year, but it is offered in response to different stimuli and will certainly have different outcomes depending on the season.

Geoff Carpentier is a published author, expedition guide and environmental consultant. Visit Geoff on-line on LinkedIn, Facebook and Instagram.

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