“…They can increase body insulation (Cherry and Verner, 1975;Rinehart-Whitt and Pagels, 2000;Kuhlmann et al, 2003), increase or decrease body mass (m b ) (Morrison, 1960;Hoffmann, 1973;Armitage et al, 1976;Heldmaier et al, 2004), increase m b -specific metabolic rate (Heldmaier and Steinlechner, 1981a) and increase the efficiency of heat production, especially by means of non-shivering thermogenesis (NST) (Heldmaier and Buchberger, 1985;Merritt et al, 2001;Bao et al, 2002). In winter, animals stay active or enter daily or seasonal torpor (Hoffmann, 1973;Lyman, 1982b;Körtner and Geiser, 2000;Heldmaier et al, 2004). Although heterothermy is generally considered to be an energy-saving strategy, it also entails considerable costs related to periodic arousal from torpor and interbout normothermy (Thomas et al, 1990;Dunbar and Tomasi, 2006;Wojciechowski et al, 2007;Karpovich et al, 2009).…”