Very true Susan, if i remember correctly forest elephants in fact communicate much further than two miles using this method.

In the jungle a whistle is next to useless. The best way to communicate over long distance is to drum on the buttress of the silk cotton tree. This gives of a deep low frequency sound that cuts through the jungle for quite considerable distances.

Another problem with high frequency sound is because it has such a short wavelength it is reflected of of obstacles a lot more so although it might stand out over other noises a little bit better it is a lot harder to determine the direction it comes from. we experience this when we first hear emergency vehicle sirens.