Are my gerbils stupid?

I just bought two gerbils and the first one learned how to climb the tubes really quickly and hung out in the top room a lot. A while after the other one did too. It's now late in the night and they haven't even tried exploring the other two tunnels. One leads to the 'observatory' and the other leads to a tunneling box where they can dig and burrow. Will they ever explore anymore or are they too stupid to care?