Rodents of Osai

Sizes are not relative, but they are all pretty small

Pittivole, the vole pokemon
Pittivole is a small normal-type pokemon that inhabits the forests, fields, and mountains of  the Osai region. They are shy and timid creatures, bullied even by bluelets and shadibugs. They aren't confident climbers, but they can use their long, flexible tails as a safety line. They can also use them to hold berries, so they can drag them to a safer place to eat in peace. They take great care of their tails and trainers are advised not to pull or tug on them. Pittivole evolves into volecal at level 18.

Volecal, the singing pokemon
Volecal is asmall normal-type pokemon common to the mountains of Osai. During evolution, the flexible tail of pittivole snaps off, and volecal never gets over its loss. To soothe its spirits, it sings from the top of its tiny lungs, though its voice is so high-pitched that very few pokemon can hear it. It is the most important food source for Arctpik, so it drags food into its burrow rather than risk feeding in the open. If volecal hear each other singing they will come to the mouth of their burrows to perform a duet. 

Denkirisu, the electric pouch pokemon
Denkirisu is a small electric-and-ground type pokemon that can be found all over the Osai region. They dig tunnels in the earth that they line with statically-charged fur - they can then use the electricity in their cheek-pouches to conduct themselves along these tunnels like a highspeed rail system. Because of the presence of these tunnels, digging in Osai can be a danger - disrupting a tunnel with a claw or a shovel will deliver a nasty shock!