I have a 5 in a 6x8 pen. BUT... I also have lots and lots of cover, and many perches for them to get away from one another but still be visible for me to inspect and take care of. I intend on breeding them soon too, so I made a pair of nesting boxes out of an old cabinet from the kitchen. Painted it dark, laid it on its back with the door facing up and cut two holes out of the side for them to walk in. I put sticks, rocks, and branches around it so it would appear to them they are inside a dark hide-spot. I left the hinges and handle on the cabinet so I can easily lift it up to check on the nesting activities.... I took a 4ft tall fir tree and cut off one side all the way down the tree and laid that side down on the floor. All 5 were hiding inside it that first afternoon.