This is a very difficult question to answer. It can vary widely depending on the volume and direction of the source, the humidity, foliage, and other factors. You may be able to hear an owl from half a mile away, but not be able to hear a mouse from a distance of fifty feet. As a rule of thumb, if you can hear it with your ears, the microphone will also hear it.
Wildlife Acoustics, Inc.
3 Mill and Main Place, Suite 210
Maynard, MA 01754-2657 USA
+1 (978) 369-5225
+1 (888) 733-0200