There are 75 species of mammals inhabiting the deserts and mountains of Big Bend National Park. Living in an area with high temperatures and low rainfall forces many animals to live extremely cautious lifestyles. Many leave their burrows only under cover of night. Others may forage during the cool early morning. Larger mammals include whitetail and mule deer, coyote, mountain lion, and black bear. The snuffling you hear around your campsite at night may be a gray fox or a javelina. Bats make up the largest portion of the park's mammal species; 20 species have been observed here, including the endangered Mexican long-nosed bat, which is found nowhere else in the United States.