The Flowing: Creatures are called 'the flowing'. When they make the journey before the bad season, they travel towards the homes in the trees. From above, it looks like a river of water flowing, as the moonlight reflects from the creatures' fur.
Bad Season: Stronger hunter type creatures emerge from their slumber and hunt accross the grasslands. They do not enter the forests where the trees protect those not of ill will.
The world is no way an attempt at realism, but a fantasy setting.
Thanks to big brother, jalonso and larwick for crit and suggestions