On two occasions I have had a doe walk right in front of the Reconyx RC60 game cam and then look direrctly into the camera. They seem to know its there. Other animals don't respond, pigs, coyotes and large deer pay it no attention. Does Bigfoot?
There is a theory that they can hear high frequency sound. The Reconyx puts out a very high, but faint, high frequency that is inaudible to human ears. It is so faint that its surprising the doe can hear it. The bucks never seem concerned. This is something I need to do more research on.
The Buck seems unconcerned. They always do.