Social behaviour and social learning The house sparrow is a very social bird. It is gregarious during all seasons when feeding, often forming flocks with other species of birds. It
roosts communally while breeding nests are usually grouped together in clumps. House sparrows also engage in social activities such as
dust or water bathing and "social singing", in which birds call together in bushes. The house sparrow feeds mostly on the ground, but it flocks in trees and bushes. At feeding stations and nests, female house sparrows are dominant despite their smaller size, and they can fight over males in the breeding season. House sparrows also have strong social learning ability, for example about novel objects in their environments. Typically, house sparrows show a lot of variation in their responses to novel objects, foods, and environments, where some individual birds are willing to approach and explore novel items, whereas others stay away, a behaviour known as "
neophobia." Captive house sparrows learned about novel objects near their food dish (and changed their behaviour towards novel objects) both from observing another individual and from hearing recorded sparrow calls.
Sleep and roosting House sparrows sleep with the bill tucked underneath the
scapular feathers. Outside of the reproductive season, they often roost communally in trees or shrubs. Much communal chirping occurs before and after the birds settle in the roost in the evening, as well as before the birds leave the roost in the morning. Some congregating sites separate from the roost may be visited by the birds prior to settling in for the night. Head scratching is done with the leg over the drooped wing. 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 cereals:
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.
Locomotion The house sparrow's flight is direct (not undulating) and flapping, averaging and about 15 wingbeats per second. On the ground, the house sparrow typically hops rather than walks. It can swim when pressed to do so by pursuit from predators. Captive birds have been recorded diving and swimming short distances under water. Two subspecies,
P. d. bactrianus and
P. d. parkini, are predominantly
migratory. Unlike the birds in sedentary populations that migrate, birds of migratory subspecies prepare for migration by putting on weight.
Breeding House sparrows can breed in the breeding season immediately following their hatching, and sometimes attempt to do so. Some birds breeding for the first time in tropical areas are only a few months old and still have juvenile plumage. Birds breeding for the first time are rarely successful in raising young, and reproductive success increases with age, as older birds breed earlier in the breeding season, and fledge more young. As the breeding season approaches, hormone releases trigger enormous increases in the size of the
sexual organs and changes in day length lead males to start calling by nesting sites. Copulation is typically initiated by the female giving a soft
dee-dee-dee call to the male. Birds of a pair
copulate frequently until the female is laying eggs, and the male mounts the female repeatedly each time a pair mates. The house sparrow is
monogamous, and typically mates for life, but birds from pairs often engage in
extra-pair copulations, so about 15% of house sparrow fledglings are unrelated to their mother's mate. Males guard their mates carefully to avoid being cuckolded, and most extra-pair copulation occurs away from nest sites. Males may sometimes have multiple mates, and bigamy is mostly limited by aggression between females. Many birds do not find a nest and a mate, and instead may serve as
helpers around the nest for mated pairs, a role which increases the chances of being chosen to replace a lost mate. Lost mates of both sexes can be replaced quickly during the breeding season. The formation of a pair and the bond between the two birds is tied to the holding of a nest site, though paired house sparrows can recognise each other away from the nest. House sparrows in natural small populations, as can occur on islands, exhibit
inbreeding depression. Inbreeding depression is manifested as lower survival probability and production of fewer offspring, and can occur as a result of the expression of deleterious recessive
alleles. Tree hollows are more commonly used in North America than in Europe, putting the sparrows in competition with
bluebirds and other North American cavity nesters, and thereby contributing to their population declines. Nests typically have external dimensions of 20 × 30 cm (8 × 12 in), but their size varies greatly. House sparrows do not hold territories, but they defend their nests aggressively against intruders of the same sex. House sparrows' nests support a wide range of scavenging insects, including nest flies such as
Neottiophilum praestum,
Protocalliphora blowflies, and over 1,400 species of beetle.
Eggs and young Clutches usually comprise four or five
eggs, though numbers from one to 10 have been recorded. At least two clutches are usually laid, and up to seven a year may be laid in the tropics or four a year in temperate latitudes. When fewer clutches are laid in a year, especially at higher latitudes, the number of eggs per clutch is greater. Central Asian house sparrows, which migrate and have only one clutch a year, average 6.5 eggs in a clutch. Clutch size is also affected by environmental and seasonal conditions, female age, and breeding density. Some intraspecific
brood parasitism occurs, and instances of unusually large numbers of eggs in a nest may be the result of females laying eggs in the nests of their neighbours. Such foreign eggs are sometimes recognised and ejected by females. The house sparrow is a victim of interspecific brood parasites, but only rarely, since it usually uses nests in holes too small for parasites to enter, and it feeds its young foods unsuitable for young parasites. In turn, the house sparrow has once been recorded as a brood parasite of the
American cliff swallow. —the soft, swollen base, which becomes harder and less swollen as the bird matures The eggs are white, bluish white, or greenish white, spotted with brown or grey. Subelliptical in shape, and an average surface area of . Eggs from the tropical subspecies are distinctly smaller. Eggs begin to develop with the deposition of
yolk in the ovary a few days before ovulation. In the day between ovulation and laying,
egg white forms, followed by
eggshell. Eggs laid later in a clutch are larger, as are those laid by larger females, and egg size is hereditary. Eggs decrease slightly in size from laying to hatching. The yolk comprises 25% of the egg, the egg white 68%, and the shell 7%. Eggs are watery, being 79% liquid, and otherwise mostly protein. The female develops a
brood patch of bare skin and plays the main part in
incubating the eggs. The male helps, but can only cover the eggs rather than truly incubate them. The female spends the night incubating during this period, while the male roosts near the nest. Eggs hatch at the same time, after a short incubation period lasting 11–14 days, and exceptionally for as many as 17 or as few as 9. The length of the incubation period decreases as ambient temperature increases later in the breeding season. Young house sparrows remain in the nest for 11 to 23 days, normally 14 to 16 days. The chicks' eyes open after about 4 days and, at an age of about 8 days, the young birds get their first
down. All the young in the nest leave it during the same period of a few hours. At this stage, they are normally able to fly. They start feeding themselves partly after 1 or 2 days, and sustain themselves completely after 7 to 10 days, 14 at the latest. ==Survival==