From November to March many people have their uros in brumation/hibernation for reproduction purposes. Mine always disappear into their hides around the end of November due to lower temperatures and light and return to "normal" in about March as the temperatures and light increase. They do come out to bask occasionally but mine never eat during that time. I have never lost a mali uro doing this with them...but it needs to be done right or you could lose one. Please read the whole section about it in the site below....its up to you to decide whether to risk it or not.
http://www.totallyreptiles.com/caresheets/lizards/maliUro.html
Read the section "Breeding of U. maliensis".
More information...
http://www.crislis.co.uk/Herps/Thatcher/urocaresheet.htm
See..."Brumation or winter rest periods."
http://www.deerfernfarms.com/Uromastyx_Care.htm
See..."Breeding"