Incubation last 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 spend more time incubating them than do 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 fouling would wet both the chicks ' plumage and the nest material , thereby reducing their effectiveness as insulation and increasing the risk of chilling the hatchlings . Nestlings 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 relining the same nest , although two broods is typical , or just one north of 48oN . Within two months , most juveniles will have moulted and gained their first basic plumage . They acquire their adult plumage the following year . As with other passerines , the nest is kept clean and the chicks ' faecal sacs are removed by the adults .