Q&A
MAMMALS
Do hibernating bears get stiff?
As bears begin their long winter sleep, it’s a reasonable question to ask. After just eight hours’ sleep, we need to stretch to get our muscles working properly again. Were we to rest for five months – as hibernating grizzlies do – we’d waste away. It takes only a few hours on a life-support machine for the human diaphragm, which powers our breathing, to weaken enough that it struggles to take over from the ventilator. Yet grizzly bears emerge from their dens pretty much as fit as they went in, albeit much lighter. How they maintain muscle mass is of great interest to medics treating muscle-wasting conditions, and several of the genes involved have been identified by studying hibernating bears. One trick bears use is to recycle proteins that would otherwise be expelled in urine, rather than raid their muscles for raw material (which also means less getting up for the loo). Stuart Blackman
ORNITHOLOGY
Where do all the feathers go?
After breeding, many birds undergo a post-breeding moult. But once all those feathers have been shed, they don’t
