Why do birds sing?
Great question, but not one we'll tackle today.
Instead, I'm curious about HOW birds sing. The variety and complexity of birdsong is amazing and hugely diverse. Listen to these YouTube samples...
Lyre bird (imitating other birds)
But what I'm really interested in is much simpler mechanics... Can a single bird sing two notes at once?
Rapid switching back and forth between two different notes is NOT the same thing. I'm curious if (and how) a bird could sing in harmony with itself!