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Feeding

As an adult, the house sparrow mostly feeds on the seeds of grains and weeds, but it is opportunistic and adaptable, and eats whatever foods are available. In towns and cities, it often scavenges for food in garbage containers and congregates in the outdoors of restaurants and other eating establishments to feed on leftover food and crumbs. It can perform complex tasks to obtain food, such as opening automatic doors to enter supermarkets, clinging to hotel walls to watch vacationers on their balconies, and nectar robbing kowhai flowers. In common with many other birds, the house sparrow requires grit to digest the harder items in its diet. Grit can be either stone, often grains of masonry, or the shells of eggs or snails; oblong and rough grains are preferred.

Several studies of the house sparrow in temperate agricultural areas have found the proportion of seeds in its diet to be about 90%. It will eat almost any seeds, but where it has a choice, it prefers corn: oats, wheat or maize. Rural birds tend to eat more waste seed from animal dung and seed from fields while urban birds tend to eat more commercial bird seed and weed seed. In urban areas, the house sparrow also feeds largely on food provided directly or indirectly by humans, such as bread, though it prefers raw seeds. The house sparrow also eats some plant matter besides seeds, including buds, berries, and fruits such as grapes and cherries. In temperate areas, the house sparrow has an unusual habit of tearing flowers, especially yellow ones, in the spring.

Animals form another important part of the house sparrow's diet, chiefly insects, of which beetles, caterpillars, dipteran flies, and aphids are especially important. Various noninsect arthropods are eaten, as are molluscs and crustaceans where available, earthworms, and even vertebrates such as lizards and frogs. Young house sparrows are fed mostly on insects until about 15 days after hatching. They are also given small quantities of seeds, spiders, and grit. In most places, grasshoppers and crickets are the most abundant foods of nestlings. True bugs, ants, sawflies, and beetles are also important, but house sparrows take advantage of whatever foods are abundant to feed their young. House sparrows have been observed stealing prey from other birds, including American robins.

The gut microbiota of house sparrows differs between chicks and adults, with Pseudomonadota (formerly Proteobacteria) decreasing in chicks when they get to around 9 days old, whilst the relative abundance of Bacillota increase.