The rabbits have some sort of fascination with the pond cover. We had one
tonight that sat there for about an hour, looking around, mostly watching
the cat watching him. I don't know if they like the cover because it's
slightly higher than the surroundings? If they like the small amount of heat
given off from the heated water (38F)? If the rabbit has a thing for my cat?
My favourite theory is that they are attracted to the vibaration, as the air
pump is mounted on the bottom side of the pond cover's hatch.

I think I've got the world's biggest bunny sex aid!