Sylvester Allred is the world s expert on tasseleared tree squirrels that live in the southwestern United States. He teaches biology to at least 700 students every year at Northern Arizona University in Flagstaff. He lives in a little cottage in the ponderosa pine forest under Mount Humphreys, the tallest mountain in Arizona, with his wife, Doctor Donna, his famous cat, Mystic, and his 4-pound dog Xena, the warrior princess.