The brown owl’s typical lifespan is from fifteen to twenty years, with a maximum recorded lifespan of twenty-two years and five months, and a theoretical lifespan ranging from fifteen years and three months to twenty-one years and nine months. The species reaches sexual maturity from six months and three weeks to two years of age. During the "Embryo" stage, the embryo develops inside an egg and is nourished by the yolk. The "Nestling" stage occurs when the owlet is in a tree cavity and is fed pieces of prey by its parents; this stage lasts from one month to one month and two weeks. Following this, the “Rapid Growth Juvenile” stage sees the young owl leave the cavity and learn to fly and hunt independently, lasting from two months to one year. The "Adult" stage begins when the brown owl can reproduce and obtain food independently, and lasts from one to twenty years.