American black bears once roamed the entire continent before it was settled by European immigrants. Due to conservation over the last hundred years, the bears have rebounded to about half the area they once inhabited. But weird things are happening to black bears lately. Their hibernation period is growing shorter, and some bears don't hibernate at all! This is especially true among "urban bears," those who hang around close to towns. The number of urban bears began to spike around 1990 in the Lake Tahoe area. A 2003 study tracked them, and found that bears that lived near towns went into hibernation a month later than more isolated wilderness bears, and awoke earlier in the spring. Five of the 38 bears did not hibernate at all.
There are two reasons for this. Urban bears have a year-round food supply in human garbage, so they don't get the nutritional cues to go sleep for a couple of months. Climate change is the other reason, as winters stay warmer longer and spring arrives earlier. One expert calculated that by mid-century, the average bear hibernation could be two to six weeks shorter than today. Read about how human activity has changed a bear's natural cycle at LitHub. -via Damn Interesting
(Image credit: Cephas)