A series of violent break-ins at multimillion-dollar homes in Aspen, Colorado, has left some residents of the wealthy ski resort afraid to go to bed at night.

But the burglars don't fit the usual profile. For a start, they typically weigh 40st (250kg). They also tend to have shaggy fur coats, and walk on four legs. When confronted, they growl. Yes, Aspen is under attack from bears. Very hungry bears, who need to munch their way through 20,000 calories a day (equal to eating one eighth of an average human) as they prepare for hibernation.