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is this nromal? it seemed like the one on the bottom was struggling a little.
is he getting bullied, or do they prefer to stack on top of each other.
and how would the one on the bottom get the uvb rays?

They do this a lot both in captivity and in the wild. I would imagine the one on the bottom must not like it too much but they don't seem to try too hard to prevent it. If they do this all the time and you're concerned about it, just make sure it's not the same guy on the bottom every time. But as long as they are getting light on parts of their bodies they will be able to absorb the UVB light.

It's called stacking and they're competing for the warmth. In large turtle colonies or communities, it's not unusual to see several stacked high. The bottom one will get less UV, though thats the nature of things. A larger basking area helps, but I think some turtles just like to stack anyway

I think in the grand scheme of things, the one on the bottom will at some point be the one on the top, so it evens out. My painteds don't like to stack, and if one gets on another's back, even partially, the one underneath usually frees himself and finds another place on the basking area.

My two always do this when they're basking. The smaller one gets on top of the bigger one. And she never seems to mind. If she did I'm sure she would push him off. They are so cute when they do this. >.<

Totally normal for them to stack like this!

Normal and cute!