When at the base, sometimes a flock of birds appears and flies from the left to the right side of the display. While the birds are flying through the sky, bird calls can be heard, as long as you are focused or zoomed in on the location of the birds in the base display. When the birds are being shown, it is possible to click on each bird, and each click causes the bird to drop out of the sky, as if the bird had been hit with an arrow, etc. However, when all the birds have been shot down, the bird calls continue to be heard, based on where the birds would have been if they hadn’t been shot down. Once the now “ghost” birds disappear offscreen, the bird calls are no longer heard, but the expectation would be for the bird calls to stop when there are no more birds flying.
This is overall a very minor thing and doesn’t effect game play.