> I have wondered if perhaps with 3 microphones positioned a specific distance apart from one another, an app could compare their relative volumes and show the user the exact location of a bird.
I am no expert, but I do know that this is possible. It's called acoustic location [1].
> Civilian uses include locating wildlife and locating the shooting position of a firearm.
As to how spaced out the microphones would have to be and to what accuracy the location can be determined, I cannot say (but my guess would be "pretty accurate").
Another interesting challenge would be to determine the location of multiple birds in different locations. Perhaps isolating specific bird calls with some ML model and then acoustic-locating that specific call. I can imagine the application showing which bird is calling from where in 3D.