Same in New Mexico, you can get a dui on a horse.
If you think about it, a bike is legally a vehicle. And the dui law does not specify motor vehicle, but vehicle. Obviously the risk to others involved is much less on a bike than driving a car or truck.
But believe me, when my brother in law was out all wasted, we were quite glad to hear he'd made it safely to jail again. He's clean and sober now thank god, but back then we were counting on the cops picking him up when he was that drunk in public. He always got caught in the car though, and cops never stopped him for biking wasted. Several times he should have been, ending up crashing the bike and going to hospital later. So hard to steer one handed with a 12 pack in the other hand.