When devising a setting for a role-playing game, some people might think considering local animals unimportant.
I do not.
I try to remember that the mundane is as important as the mysterious. For instance, I will mention animal scat, deer tracks, flights of birds, bird calls, etc., while on a wilderness trek. Why? First off, I want to ensure that the world feels "alive" -- things are where they should be. There are mice in the ruins, birds in the fields, and a fox in the henhouse.
Secondly, this allows for some quick action within the game. On a riverboat, a stag is sighted on shore. A quick bet is made on whose shot can bring it down, and there will be venison for dinner. Hearing wolves howl in the distance need not presage an instant attack -- the PCs will travel this wild area again. Without the foreshadowing, though, an encounter with wolves can seem rather "out of the blue". Likewise, a partially-eaten deer carcass can indicate the presence of wolves to wilderness-minded sorts, like rangers and druids.
Finally, including animals on a regular basis prevents "ringers" from being obvious. If you never mention ravens, then that raven is obviously a familiar or spy. If you never mention rabbits, that you do so now means there's a wolf-in-sheep's-clothing lurking nearby. That you never mention wolves is a sure sign that the one you are encountering now is more than half likely to be a werewolf.
Some games/Game Masters take this even farther. Why have horse, when you can have firehooved scalehorses? Why have bears when you can have hardgrapple biteybears?
The answers are the same -- unless there is something "normal" in the world (as the world defines "normal"), immersion is damaged. If everything you encounter is monstrous, you will respond to everything as though it were a monster.
Sorry, but No Thank You.
My game still has room for lions, and tigers, and bears. And songbirds. And mice.