The UTHF is home to many animal species. Although it is nearly impossible to cyclopedically determine the insect fauna, numerous intensive studies have been conducted to investigate specific groups of insect fauna. Regarding mammals, 33 out of 53 species present in Hokkaido have been confirmed in the UTHF. Bird and fish fauna have also been studied. To date, a total of five orders, 40 families, 84 genera, and 121 species of birds have been recorded, including three species designated as the natural monuments of Japan. In terms of fish, a total of nine species have been documented, including two introduced species and one hybrid.