 Incubation lasts thirteen days , although the last egg laid may take 24 hours longer than the first to hatch . Both parents share the responsibility of brooding the eggs , but the female spends more time <unk> them than does the male , and is the only parent to do so at night when the male returns to the communal roost . The young are born blind and naked . They develop light fluffy down within seven days of hatching and can see within nine days . Once the chicks are able to regulate their body temperature , about six days after hatching , the adults largely cease removing droppings from the nest . Prior to that , the <unk> would wet both the chicks ' plumage and the nest material , thereby reducing their effectiveness as <unk> and increasing the risk of chilling the <unk> . <unk> remain in the nest for three weeks , where they are fed continuously by both parents . Fledglings continue to be fed by their parents for another one or two weeks . A pair can raise up to three broods per year , frequently reusing and <unk> the same nest , although two broods is typical , or just one north of <unk> . Within two months , most juveniles will have <unk> and gained their first basic plumage . They acquire their adult plumage the following year . As with other <unk> , the nest is kept clean and the chicks ' <unk> sacs are removed by the adults . 
