Hibernation is the obvious exception. But there are also a very few cases where mammals are just not very good at generating internal heat :
Respect also to those who gave a shout out to the naked mole rat. "Naked mole rats are interesting from a thermoregulatory standpoint, because they don't control their body temperature very well," says Boyles. This does not mean they are failed mammals. Rather, it is simply that they spend all their lives in underground tunnels where the temperature is fairly predictable, usually somewhere between 29 and 32C."They don't have to spend the energy on thermoregulation," says Boyles. "It's the perfect example of an evolutionary adaptation, not a physiological limitation."
Finally, Jennifer Jones highlighted an extinct species of goat called Myotragus balearicus. It has been claimed that this goat was properly ectothermic: that is, entirely dependent on heat from its environment. The evidence is indirect. "The bone microstructure indicates that Myotragus grew unlike any other mammal but similar to crocodiles at slow and flexible rates," wrote researchers in 2009. This is suggestive of ectothermy, but it is a long way short of proof... It is an intriguing idea. However, we could not find a follow-up to the 2009 study, so for now it is not clear if M. balearicus was truly ectothermic.
http://www.bbc.com/earth/story/20160609-time-to-bust-a-myth-not-all-mammals-are-warm-blooded
But bear in your image is a warm blooded animal.
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