Its legs and bill are also black. As it nears a month in age, the duckling's plumage starts becoming drab, looking more like the female, though more streaked, and its legs lose their dark grey colouring. Two months after hatching, the fledgling period has ended, and the duckling is now a juvenile. Between three and four months of age, the juvenile can finally begin flying, as its wings are fully developed for flight (which can be confirmed by the sight of purple speculum feathers). Its bill soon loses its dark grey colouring, and its sex can finally be distinguished visually by three factors: 1)the bill is yellow in males, but black and orange in females; 2)the breast feathers are reddish-brown in males, but brown in females; and 3)in males, the centre tail feather (drake feather) is curled, but in females, the centre tail feather is straight. During the final period of maturity leading up to adulthood (6–10 months of age), the plumage of female juveniles remains the same while the plumage of male juveniles gradually changes to its characteristic colours. This change in plumage also applies to adult mallard males when they transition in and out of their non-breeding eclipse plumage at the beginning and the end of the summer moulting period. The adulthood age for mallards is fourteen months, and the average life expectancy is three years, but they can live to twenty. Several species of duck have brown-plumaged females that can be confused with the female mallard. The female gadwall ("A.strepera") has an orange-lined bill, white belly, black and white speculum that is seen as a white square on the wings in flight, and is a smaller bird. More similar to the female mallard in North America are the American black duck ("A.rubripes"), which is notably darker-hued in both sexes than the mallard, and the mottled duck ("A.fulvigula"), which is somewhat darker than the female mallard, and with slightly different bare-part colouration and no white edge on the speculum. In captivity, domestic ducks come in wild-type plumages, white, and other colours. Most of these colour variants are also known in domestic mallards not bred as livestock, but kept as pets, aviary birds, etc., where they are rare but increasing in availability. A noisy species, the female has the deep "quack" stereotypically associated with ducks.