Frog choruses are very appealing, and make some of the most musical of nature recordings. Which is odd in a way, because frogs have very little vocal expression. Sure, they make great noises, but they are unable to modify their vocalisations or express feeling in the way that mammals or even birds are able to. When a frog makes its call, it just… makes its call.
Here is a picture that illustrates what I am talking about. This shows the waveform of a recording from our recent album ‘Frogs, Frogs, Frogs!’. Time flows horizontally from left to right, and the amplitude (volume) of the sounds registers vertically. It shows about 10 seconds from track 16; ‘Striped Marsh Frogs (Southern race)’. These frogs have a sharp and quite loud clicking sound, and you can see each frog ‘click’ as a vertical line, where the volume of each frog (there are several calling here) is indicated by the height of the line.
What is remarkable is that the volume of the clicks from each frog is nearly identical. I have drawn some lines on this waveform to indicate the calls of individual frogs.
Thus you can see that when a frog makes its call, it has little control over the volume or expression of its vocalisations in a way that we take for granted. Considering that amphibians are a primitive family of animals, and have limited vocal apparatus, this is understandable.
Of course individual frog sounds do vary quite considerably, but this is often a factor of their body temperature, derived from the ambient environmental temperature. Sometimes these variations, affecting pitch and frequency of calling, can be so great that frogs of the same species can sound like another altogether. An example of this can be heard also on the album: compare the spotted marsh frogs heard in the background during tracks 5 or 8 (rapid “uk-uk-uk” calls), with the chorus of them on track 14. You can hear the lower pitch and slower rhythms very clearly, its the same species, but you’d be excused for thinking it wasn’t.
And just to give an example of racial differences, compare the ‘click!’ sound of the southern race of the striped marsh frogs we were looking at earlier, with the tennis-ball-like ‘whuck!’ of their northern cousins (track 5).
So given their ‘limited’ vocalising abilities, what makes frog sounds so appealing to us? Well, for me, lots of things, principle among them rhythm and texture. The tones of different frog species can be fascinating; chiming, bleating, clicking, croaking, moaning, laughing, whistling, purring… there is an endless variety to frog sounds. They seem to do everything – except curiously “rrri-bit”, I’ve yet to hear a frog do the classic “rrri-bit”!
Frogs also set up great polyrhythms. These rhythms are important and purposeful, a part of frog’s evolutionary survival strategy. In a dense frog chorus, complex overlapping and interlocking rhythms allow each individual frog to be heard, while simultaneously confusing predators who may be trying to locate one frog by its call.
The frog choruses on our ‘Frogs, Frogs, Frogs!’ album were recorded in diverse habitats across Australia, from tropical rainforests in the north, to the outback after rains, and bush waterholes in the east and south. Each chorus has something that may appeal to you, from the familiar calls of pobblebonks that open the album, to the extraordinary moaning of western spotted frogs that conclude it.
Both are included in a sound sample from the album, which you can listen to here.
‘Frogs, Frogs, Frogs!’ is available for exclusive download from the Listening Earth wesbite.
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This sound collection is very interesting! I’d like to hear some of it, just to compare to sounds of brazilian frogs. Some frogs here are incredible, by looking at the spectrograms you just wonder if it’s art or what? I tell you, it IS art, nature art!
Hi, your comments are apt, frog calls are more-or-less hard-wired and not really like bird songs but I don’t think this is not quite the full story. Frog calls often do vary with situation and motivation. Your example from Marsh Frogs looks like an antiphonic chorus in which individuals syncopate their calls to distinguish themselves from others. Each frog is calling at maximum volume trying to outdo his rivals. The differences in volume would be mainly due to distance from the microphone (as well as body size). There would have more individual variation in volume and regularity when calling alone or in a small hesitant group after disturbance. Striped Marsh Frogs are also a poor example because these very simple clicks are their full repertoire. There are plenty of frog species that use multiple motifs to create more complex calls – such as mixing male to male spacing motifs with the typical male to female mating calls. Some species, such as the Litoria fallax group, have many more variations and mix and match to create different calls from different individuals, no-one is really sure why. Also there are some species which seem to have really relaxed consistency constraints and vary from one call to the next, the African River Frogs do this with a constantly changing series of grunts, ticks and burps that sound like rocks rolling over each other in a stream. In any case, this really misses the point. For me the appeal of frog calls is in the diversity of sounds among species and their almost but not quite regular rhythm and tempo that creates a seemingly incessant chorus – that periodically stops abruptly and then slowly regains the score, species by species, individual by individual.