Wildlife of Yellowstone Elk Male antlers can weight about 30 pounds (14 kg) per pair and are shed every year They are the most abundant large mammal in Yellowstone. Calves are born with white spots to help them hide from predators. River otters These playful creatures are the most aquatic member of the weasel family. They are crepuscular which means active in morning and evening hours. They can stay underwater for eight minutes. Their fur is waterproof and helps them manage their body temperature. Yellow bellied Marmots Marmots are one of the largest rodents found in the park. They live in open grassy habitats with rocks nearby, and can be found from the lowest valleys all the way up to alpine tundra. These animals are herbivores which means they are vegetarians and eat flowers, grasses and seeds. One Fu...