Your Bunnies need energy to dig, mine and breed. Energy can be gained by either feeding your bunnies food or by placing them on certain furniture that can regenerate energy over time. Energy will restore to the maximum amount of energy your bunny can hold when the specific bunny levels up, and will gain 10 more energy per each level up. Energy is calculated using this mathematical formula: BUNNY LEVEL*10. Digging more deeper will result in more energy loss for your bunnies.