Route 101, the first route which Trainers from Littleroot Town traverse on, is home to a wide array of different Pokémon. Hence, Professor Birch often performs his studies here. Heading north from Littleroot, the route forms a "U", turning north and immediately backpedaling east near the first patch of grass. A ledge blocks the way north, letting only southbound travelers avoid the grass. Route 101 then turns north into another patch of grass as it heads west. At this point, the path travels through the last of three grass patches. Route 101 then turns north as it enters Oldale.
In Pokémon Omega Ruby and Alpha Sapphire, after battling with Brendan/May on Route 103 and returning to the lab, the player will receive the DexNav application at the entrance to Route 101. Near Oldale Town, Brendan/May will explain the mechanics of hidden Pokémon, then a hidden Poochyena will appear. If the player succeeds in sneaking up to the Pokémon, the encounter will be a level 5 Poochyena that has an elemental fang attack as its first move; if the player scares it away, enters another battle, or leaves the area, the Poochyena will not reappear.
In Pokémon Omega Ruby and Alpha Sapphire, Professor Birch will give the player more starter Pokémon from other regions if the player has completed certain milestones. The following starter Pokémon are available:
Sinnoh starter Pokémon (Turtwig, Chimchar, and Piplup): after entering the Hall of Fame for the second time (and after choosing an Unova starter)
If the above conditions are met, then the next time the player exits their house in Littleroot Town, Professor Birch will be heard yelling for help from Route 101. When the player arrives to help, they will be allowed to choose one of the starter Pokémon.