Which is akin to dragging a single finger across different piano keys. Only a single frequency, or note, played at a time. This is common among songbirds.
Contrast that with the sound of a crow. The sonogram is much more broadband in signature. This is akin to mashing a bunch of keys on a piano all at the same time. Many frequencies present at simultaneously.
I think there's a key difference.
Assuming this is the spectrogram of single note being played on the Piano (https://soundshader.github.io/hss/gallery/piano/2.jpg) (which I can't be certain of, since the audio sample wasn't provided). Seems like a single piano note fires on multiple frequencies, and our ear 'aggregates' them so we hear it as a single note.
Songbird belts out a single frequency at each point in time. We still hear a single note but there's nothing to aggregate.
At least that's my interpretation of the parent comments. Again, can't be sure.
Crows, in the morning, seem to be broadcasting work gang related information, organising their crew to go and harvest certain regions, then report back on the yield.
If songbirds are courting, and hence broadcasting different information, for different purposes, I wonder if some generalisable differences might be apparent in the receiving birds brains.