An interesting article about how early man may have heard the world.
"It appears the ancient hominins had a greater sensitivity to higher frequencies, from around 1.0 - 3.0 kHz, when compared to either chimpanzees or modern humans. This, the researchers suggest, could be an adaptation to living on the savanna, where sound waves don’t travel as far as in the forest canopy and where animals have to rely on short-range communication."
As noted in the above quote, sound often travels best when it has structures and matter to "bounce off of," such as trees. Higher frequencies can be easier to hear in short distances thus leading to this discovery.