Ever wonder what it is that birds are singing about? Here is a summary I wrote of an article that looks into the nature of song transmission and maybe its meaning.
Eavesdropping avoidance and sound propagation: the acoustic structure of soft song
Animal Behaviour (2017) 134:113-121,
Luis E. Vargas-Castro, Luis Sandoval, William A. Searcy
When you shout to an auditorium full of people are you using the same language as when you whisper sweet nothings to your loved ones? Inherent to your message is your intended audience. Animals too craft their messages for lovers, foes in their territory, and eavesdropping predators.
Is volume the only disguise for your message to the intended receivers? Birds commonly contend with a variety of listeners—they’re not singing for our pleasure! Some birds have a broadcast style song or a soft song. However a deeper look identifies a much more complex control over communication.
Researchers evaluated broadcast vs soft songs for several physical components of song transmission (distance from source, speaker height, and microphone height) as well as spectral components (signal attenuation, signal-to-noise ratio, and blur ratio). Furthermore in this analysis, 18 song syllables were used in the forest of Talamanca mountain range of Costa Rica. Soft syllables are more complex in frequency patterning yet with a lower amplitude; therefore, the soft syllables were modified with a lower frequency component yet same temporal pattern to further understand signal transmission.
Soft songs disproportionately attenuated the signal, indicating they were indeed more structurally useful at close distances. Similarly, the blur ratio, or frequency dependent distortion of signal amplitude, was worse for soft songs. The broadcast song had the clearest signal-to-noise ratio, making it the best for farther away listeners. The spectra of the signals (broader and more frequencies included for soft songs) contributed to the song degradation and attenuation. The modified song syllables showed an intermediate response.
These results support the idea that the songs themselves, structurally, are suited for the type of information present. The more complex soft songs are likely not intended for any listeners outside of a territory but are adapted for the close or short-range communication. Conversely the broadcast songs can travel with less song degradation over 2-4 territories. Understanding structural differences in song actually mechanistically suited to transmission type adds a whole new layer to singing and communication.