House sparrows are gregarious in nature and will form flocks for roosting, feeding and dust-bathing. This sociability also extends to the mating season, because although they generally pair for life, house sparrows are known to be rather promiscuous, with one DNA study finding that 15 percent of chicks were from a bird different to the parents. House sparrows take advantage of their urban environment and nests will be built under roof tiles, in air ducts, and various recesses. A good nest site will be used several years running. Females will lay 3-5 eggs and can raise up to 4 broods a year.