A FLIR E6 infrared thermal camera (FLIR Systems, Wilsonville, OR) was used to measure surface body temperature (14 (link)). After mice were removed from nests, the surface temperature was immediately obtained using a double-blind protocol. During capture of thermal images, animal behavior and scanning distance were controlled to avoid artificial effects. For reduction of variances, rectal body temperature was also measured using a highly precise electronic thermometer (TH-5 Thermalert Clinical Monitoring Thermometer; Physitemp Instruments).