Calcium is the nutrition for all animals to maintain their body. Bones and teeth are made of calcium. Muscle and brain also need calcium to work well. Lemmings are rodents, living in tundra. They need calcium too. Even though they are herbivore, lemmings gnaw on anyway. Chewing is most important work for rodents.

Lemmings are one of the staple foods for tundra predator such as arctic fox, wolf and seabirds. Snowy owls depend on lemmings too. Especially for their eggs, lemmings are essential to form hard eggshells.

Spitsbergen is the island of Norway. It is located in approximately halfway between mainland Norway and the North Pole. That sounds very cold, but it is not so cold. Since the North Atlantic current warms up the temperature, the average summer temperature is about 6 °C(43 °F) and the winter is −16 °C (3 °F). Spitsbergen is the home for many arctic animals such as seals, beluga whales, bowhead whales, walruses, reindeer and polar bears.

Despite of the size Polar bears attack walruses. Panicking walruses could be easy targets for polar bear to assault while avoiding deadly long tusk.