The problem with ambient sounds is that they are currently completely unlinked to player, zombies, or animals. So we become very quickly accustomed to which sounds are relevant to us, and the ambient sound becomes meaningless, it is nothing more than white noise in the background.

To resolve this, certain ambient sounds could have a greater chance of being triggered by players, zombie and animals. This is necessary to prevent the ambient sounds becoming white noise. If the twig breaking sounds are more prevalent when a player or animal moves through a dry forest, or the gate/fence creaking sound is more prevalent when zombies/players move past chain link fences or through open gates, or if birds being startled happens more often when players make too much noise or disturb a certain tree, then these sounds can never become meaningless background noise to players since there will always be an increased chance that they are telling us something important about our surroundings, and thus have a very positive impact on their relevance to the game-play.

The fact they can still occur as ambient sounds would mean that they don't become entirely predictable as means to read the game. It just gives us an idea as to what may be going on in our surroundings.