Breeding season: May–September, 2 broods per year (sometimes 3 in warm years). - Nest: A half-open, cup-shaped mud nest built from saliva-coated pellets of mud and grass stems, lined with feathers; fixed to a beam or wall indoors, 1–5 m up; the same nest is used year after year and is gradually enlarged. - Eggs: 4–5 eggs, white with reddish-brown speckles; incubation period 14–16 days; both parents incubate. - Young: Fed intensively by both parents with balls of insects; they leave the nest after 18–23 days and are fed for a further 1–2 weeks.