So according to the Patch Notes...

#Udyr Mana costs reduced

"Back in 7.8 we made some adjustments to everyone’s favorite ManBearTigerTurtlePhoenixMonkey. Within that set of changes we tweaked Udyr’s mana costs to decrease per level bla bla bla..."

http://i.imgur.com/S0zJdQa.png?noredirect