There is something like this currently under development. There is a problem though: my noise generators are supposedly active across the whole hearing range, from 20Hz to 20kHz. And birds are only producing frequencies above 1000Hz. So, I need to fill up the bottom sliders with other sounds, or find... really big birds! ;-)
perhaps a combination of birds and ocean waves, or frogs, or yes, big birds :) ... It'll be a little puzzle, but +1 for more nature sounds! .. and perhaps one of my favourites: tibetan gongs!
I tried this before... but it doesn't sound anything like a known animal. But who cares actually, if the noise title is right? ('Imaginary Birds') So, let's try it again ;-)
Everything feels better when listening to the Dawn Chorus.