It’s a simple fact that black bears spend their whole life following their stomachs, including in winter. Similar to the postman’s motto, “neither snow, nor rain, nor heat, nor gloom of night,” keeps a bear from eating its fill. So for bears in Yosemite, winter denning is not associated with the weather so much as it is linked to food availability. There are years when oak trees make an over-abundance of acorns, considered a mast year, and bears can been seen all winter digging under feet of snow to feast on acorns. Similarly, it has been reported in other areas that bears will rouse from winter dens to take advantage of trash cans that are put out curbside every week on trash day. So while bear behavior can be motivated by both human and unnatural foods, it is not uncommon to find bear tracks in the snow and it is important to always lock up food in a hard-sided structure or in a food locker when visiting Yosemite.