Hi, my map turtle does that as well, and sometimes his legs, are tucked under when he is basking under his light. which is upper 80's to low 90's,I know he is warm enough, I see this mostly when he is tired, I think it is his way of being cozy... It is usually in the evening towards the time I switch bulbs to a red infra bulb....he is fine..just tend to be tired when they tuck everything under their shell.... Hope this helps...sincerely, Susan.