Breeding can occur in any month but is most common from March through August. The male usually selects a nest site and controls a territory centered around it. Nests are bulky, roofed affairs, built haphazardly and without the good workmanship displayed by other weaver finches, the group to which the house sparrow belongs. Sparrows are loosely monogamous. Both sexes feed and take care of the young, although the female does most of the brooding. From 3 to 7 eggs are laid, 4 to 5 being the most typical. Incubation takes 10 to 14 days, and the young stay in the nest for about 15 days. They may still be fed by the adults for another 2 weeks after leaving the nest.

House sparrows are aggressive and social, both of which increases their ability to compete with most native birds. Sparrows do not migrate. Studies have shown that 90% of the adults will stay within a radius of 11/4 miles (2 km) during the nesting period. Exceptions occur when the young set up new territories. Flocks of juveniles and nonbreeding adults will move 4 to 5 miles (6 to 8 km) from nesting sites to seasonal feeding areas.

Mortality is highest during the first year of life. Few sparrows survive in the wild past their fifth season. One individual, however, lived in captivity for 23 years. While house sparrows are tolerant of disturbance by humans, they can in no way be considered tame. Their success lies in their ability to exploit new habitats, particularly those influenced by humans.

House sparrows consume grains in fields and in storage. They do not move great distances into grain fields, preferring to stay close to the cover of hedgerows. Localized damage can be considerable since sparrows often feed in large amounts over a small area. Sparrows damage crops by pecking seeds, seedlings, buds, flowers, vegetables, and maturing fruits. They interfere with the production of livestock, particularly poultry, by consuming and contaminating feed. Because they live in such close association with humans, they are a factor in the dissemination of diseases (chlamydiosis, coccidiosis, erysipeloid, Newcastle’s parathypoid, pullorum, salmonellosis, transmittable gastroenteritis, tuberculosis, various encephalitis viruses, vibriosis, and yersinosis), internal parasites (acariasis, schistosomiasis, taeniasis, toxoplasmosis, and trichomoniasis), and household pests (bed bugs, carpet beetles, clothes moths, fleas, lice, mites, and ticks).

In grain storage facilities, fecal contamination probably results in as much monetary loss as does the actual consumption of grain. House sparrow droppings and feathers create janitorial problems as well as hazardous, unsanitary, and odoriferous situations inside and outside of buildings and sidewalks under roosting areas. Damage can also be caused by the pecking of rigid foam insulation inside buildings. The bulky, flammable nests of house sparrows are a potential fire hazard. The chattering of the flock on a roost is an annoyance to nearby human residents.

Nestlings are primarily fed insects, some of which are beneficial and some harmful to humans. Adult house sparrows compete with native, insectivorous birds. Martins and bluebirds, in particular, have been crowded out by sparrows that drive them away and destroy their eggs and young. House sparrows generally compete with native species for favored nest sites.