22 July 2011
House sparrows usually nest in loose colonies and since they don't defend a proper territory, nests can be as little as 20-30 cm apart.
Nests are often placed in holes and crevices within buildings and they will readily use nestboxes. Free-standing nests are also frequently built, in creepers against walls and in thick hedges or conifers.
Pairs often remain faithful to their nest site and to each other for life, although a lost mate of either sex is normally replaced within days. A hole is filled with dry grass or straw with a nesting chamber lined with feathers, hairs, string and paper. Feathers may be plucked from a live pigeon!
The main nesting season is from April to August, although nesting has been recorded in all months. Most birds lay two or three clutches, but in a good year fourth attempts are not uncommon.
The female lays two to five eggs at daily intervals and often starts to incubate part way through egg-laying. Both sexes incubate, and the chicks hatch after 11-14 days. The parents share nesting duties equally. Chicks are brooded for 6-8 days, but can control their own body temperature only when 10 or 11 days old.
The youngsters are fed on a variety of invertebrates, including aphids, caterpillars, beetles and grasshoppers. Seeds and vegetable matter are also given, particularly during periods when invertebrates are scarce (e.g. cold weather) and become more important after the chicks leave the nest.
The young fledge 14-16 days after hatching. They are unable to feed themselves for about a week after leaving the nest and are cared for by their parents for around a fortnight. Post-fledging care is frequently left to the male as the hen prepares for the next brood. She can begin laying her next clutch of eggs within days of the previous brood leaving the nest.
Newly independent young often gather in large flocks, anywhere there is an abundance of seed, invertebrates and other suitable foods. These may be areas of wasteland or around garden feeding sites. Later, rural flocks may move on to grainfields to feed on the ripening grain, often joined by adult birds, once they have finished nesting. Flocks tend to break up through the autumn and birds return to their nesting colony sites.