Black bears are very abundent throughout Yosemite! They are often brown and while not usually agressive, keep your distance! Do not leave any food in your car, not even an empty ice chest. Bears have learned that an ice chest means food and they can and will break into your car to find it. Bears can smell a donut from over a mile away. Don't even leave a stick of gum in the glove compartment! Always use bearproof lockers supplied around the park.
All these warnings of bears and I didn't even see a squirrel! No bear sightings that I can report of. Though one night we were awaken by the howls of coyotes/wolves.