For most species, the amount a fetus grows before birth determines the length of the gestation period. Smaller species normally have a shorter gestation period than larger animals.[2] For example, a cat's gestation normally takes 58–65 days while an elephant's takes nearly 2 years (21 months).[3] However, growth does not necessarily determine the length of gestation for all species, especially for those with a breeding season. Species that use a breeding season usually give birth during a specific time of year when food is available.[2]