Recording bird calls using sonograms
Knowing bird calls is important
Some birders just seem to be able to come up with the name of a bird simply by hearing the call. Even more impressively, they say things like "there's a Musk Lorikeet inamongst the Rainbows".
In a situation like this, my reaction is to ask "how do you know? What does that call sound like? I can hear dozens of birds, what am I listening for?"
Remembering bird calls is a huge part of birding. Certainly, a good knowledge of calls is crucial to identifying what birds are around you.
Let's say I'm out in the field, after a particular target bird. I can play the call (without disturbing the bird), and that'll stick in my mind for a while. But how can I remember it permanently?
But how can you do it?
|My mate Peter with a shotgun mic|
A call is complex. There are different pitches, slurs and tones. Some are even polyphonic, with different pitches going at once.
Being able to tease out some components helps a little. But how do I describe the plate of spaghetti that makes up a call?
So my most basic problem is to be able to get inside what can be a cacophony of different and complex noises, and identify each component. Once I can do that, I'll have something to describe. Once I can describe them and take notes, I've got a chance of remembering the call for next time, as well as being able to talk with others in an understandable way.
Enter the spectrogram (also known as a sonogram). This shows how pitch changes over time for a call.
You can see rising or falling notes, fast or slow chirps, harmonics and even polyphony.
It's just like how an old pianola roll works - the top notes are up the top of the graph and the low ones are down the bottom. You can literally see what's happening.
Here's a couple of simple examples from the BOCA calls CDs - the Horsfield's and the Shining Bronze-cuckoos. The Horsfield's call is a descending whistle, a bit more than a half second in duration, and with a slightly longer gap between each.
The Shining's call is a faster, purer (with no harmonics) upwards whistle. There are about two per second with a similar gap between each. There's an echo around the Shining's call, which you can see by a "smear" moving rightward from the lines, but that might be the recording.
See how much we can now say about the calls? Far more detailed than "a descending whistle or a faster upwards one"!
It's an objective way of displaying sound and all its components. I can use it as a language to talk about calls with others.
I created these using free software called Raven Lite, distributed through Cornell University.
Using a spectrogram, you can record a call, print it, and keep it with your notes. It gives you even more detailed information about the call than I've discussed here, including noise, trills, harmonics and other details of the call. It solves that cascade of problems I started this post with!
Being able to identify these details, you can remember and recognise them in the live calls you hear.
This will make you a better birder.
Sonograms show you a literal picture of a bird call. You can see how pitch, tone, and other components change through the call.
Have a look at a few more examples. They're snippets of calls from the BOCA tapes.
Harmonics: the Rainbow Bee-eater
The Rainbow Bee-eater's call is a series of short bursts, about four per second. The base part of the sound is very broad, covering a wide range of frequencies. This indicates the raspy, noisy quality of the base of the Bee-eater's call.
Harmonics (the lines above the main ones) change the tone of the whistle. Some people say it makes the sound more "rich". However, too many harmonics makes the overall sound chirpy and "noisy".
If you look closely at the top harmonic of the Bee-eater's call, you'll see that it's in fact another series of very short sounds, which give each burst a rattling quality. Most humans can't hear this harmonic, but it's there, repeated in the lower registers as well. I think it sounds like an umpire's whistle.
Pitch: the Mallee Emu-wren
An important thing to see is the scale on the left of the sonogram. It shows the pitch of the sounds in kilohertz. Most of the calls I've talked about are in the 2-5 kHz range. But look at the call of one of my bugbear birds, the Mallee Emu-wren. The pitch of this call is up around 8kHz, with nearly nothing below about 6kHz! This is the reason I have trouble hearing these little blighters - it's pretty much too high for my ears.
Looking closely at the sound: the Spotted Nightjar
One that shows a combination of aspects is the Spotted Nightjar (one of my favourite desert calls). It's a low call, nearly entirely under 1kHz. It starts with a slowish whistle, speeding up gradually before breaking into what sounds like a maniacal rattle. But the sonogram shows this last bit isn't random sound, but a very precise and fast repetition of two low whistles, one higher than the other.
A complex call: the Redthroat
Finally, one I'll leave you with - the Redthroat. See if you can "hear" the call by reading the spectrograph.