The main prey in the tundra is lemmings, which is why the white fox is often called the “lemming fox.” The white fox's reproduction rates reflect the lemming population density, which cyclically fluctuates every 3–5 years. When lemmings are abundant, the white fox can give birth to 18 pups, but they often do not reproduce when food is scarce. The “coastal fox” or blue fox lives in an environment where food availability is relatively consistent, and they will have up to 5 pups every year.