Just because they eat birds doesn't mean they have to climb to do so or that that one specific snake actually climbs a tree every time it's hungry. I am sure it happens a lot and I have seen them climb myself, but I think that was due to moving into a new home and still getting used to it. After they got used to their new homes they would hide in their hides on cool/warm sides and nothing more other than coming to get some water or eat or poop.