Much like a human baby, their heads are too heavy to support on their own. Once they are big enough, they’ll sleep sitting up. Their leg muscles are designed in a way that their tendons will keep them locked into their branch of choice while they sleep until they actively let go.
Follow-up question: why do they do it?
Much like a human baby, their heads are too heavy to support on their own. Once they are big enough, they’ll sleep sitting up. Their leg muscles are designed in a way that their tendons will keep them locked into their branch of choice while they sleep until they actively let go.