[birdbrain]

I don't want to detract from the images, or the work that went into this, but, er, there are a lot of types of birds. Just among passerines (songbirds), we're talking over 6,000 species.

So any sweeping statement like "birds don’t seem to bother to create a complex multi-layered harmonics pattern" is practically guaranteed to be wrong. And so it is. Lots and lots of birds sing incredibly harmonically complex songs. Browse any of these (https://www.remoteenvironmentalassessmentlaboratory.com/expl...) if you're interested - it's a tiny sample of birds, and many, many of them do in fact have harmonically complex songs.

[crazygringo]

You may be misunderstanding, though your username is very appropriate. :)

"Harmonics" here isn't referring to the harmonic complexity of songs.

It's referring to harmonics as in overtones, the complexity of the overtones -- the timbre.

It's the voice of the bird, not the songs it sings.

[birdbrain]

I should have been clearer. I am also talking about moment-to-moment spectral complexity or entropy.

I agree that the point TFA is suggesting seems to be about the spectral complexity at any given moment in song - what you might call the timbre - and how nearly pure the tones in their spectrograms are. (They don't specify what species they're showing. Looks like several, but I can't ID them by eye.)

My point is that no, in fact, many bird species produce vocalizations that are indeed spectrally complex (beyond even just harmonic stacks) from moment-to-moment.

Take a look at song from a blue jay (https://www.remoteenvironmentalassessmentlaboratory.com/expl... ; not the best example, or one I produced, but an easy one to hand), particularly the syllables near the end of the clip. That's an example of a complex timbre.

And lots of species produce song and calls with features like this.

[cma]

Harmonically complex is unrelated (unless they do something like Tuvan throat singing), but the species thing is a good point.

Compare a parrot or a crow vocalizing. From that it seems some can control the amount of overtone or at least can use two different modes or something.

Seems almost like comparing humans whistling vs speaking or something (assuming whistling is closer to a pure sine tone).

[birdbrain]

See my reply to your sibling comment - I do in fact mean spectral complexity at any given moment, not just over the course of the song. Many species of birds can and do vocalize with complicated timbre, including harmonic stacks, buzzes, clicks, and others harder to characterize.

And it's great that you bring up the possibility that two modes might be engaged. The avian vocal organ, the syrinx, has two sets of membranes which can vibrate as air is passed over them. Many species (particularly, as you'd expect, the ones best at imitation, like corvids, parrots, lyrebirds, etc) are able to control these two sources independently (but even those which generally don't control them separately can produce syllables with rich timbre), layering a harmonic stack with a click or a buzz.

I feel I should reiterate: nothing here is meant to detract from TFA's demonstration of what looks like a nice acoustic analysis tool. But TFA is, unfortunately, just plain wrong in its conclusion that birdsong is mostly pure tones.

[aulin]

seems like selection bias, plenty of birds have both simple tone songs and harmonically complex vocalizations, if you just draw images from the first sample you will get nice single tone pictures