I think that every budgie wants to be higher than the other, and height means safety on the wild. Ya know, flying to the highest branch to keep the ground predators away while they sleep. Do you turn the light off unexpectedly? This may cause the sudden rush to the top that you described. c:

In the wild budgies sleep in trees above the ground. I'm sure its just their natural instincts cx

every night, when i turn off the light, the budgies will rush to the top of the cage, they will even climb onto the hoop even though they have to balance on it. when i mean on hoop, i mean they climb next to the hook that connect the hoop to the cage...are they afraid at the bottom? :3 so cute.