One of the most typical animals of the tundra is the lemming, a small rodent. Lemmings reproduce very quickly and reach sexual maturity very early in life: when they are 38 days old, the females can already give birth. When the population is most numerous, lemmings devour all the plants they can find. To look for more food, these rodents migrate to amazing lengths, during which journey many of them die. They move all together to food-richer areas, often across rivers, short stretches of sea and towns.