House sparrow

• 1. Introduction

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  The house sparrow, a bird about 16 cm long, has been recorded breeding in an English coal mine 640 m below ground. It has also been seen feeding at night on the observation deck of the Empire State Building. Few wild animals turn up in places so unlikely. This small brown and grey bird, known to science as Passer domesticus, is found in most parts of the world. How did it become the most widely distributed wild bird on the planet? Why has a creature so numerous, and so often treated as a nuisance, begun to vanish from cities that once rang with its chirping? And what does a bird that follows people everywhere reveal about the people it follows?

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• 2. Plumage and Voice

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  A breeding male house sparrow carries a black bib across his throat and chest, framed by a dark grey crown and chestnut patches on the sides of his head. The female lacks the bib and the grey crown entirely. She is a buffish brown, with darker streaks on the back and a pale stripe above each eye. Her bill is brownish-grey, while his turns black for the breeding season.

  In winter the male looks duller, because pale tips cover many of his feathers. Wear and preening gradually strip these away and reveal the black and brown beneath. The size of the bib varies from bird to bird, and some researchers proposed that it signals social status or fitness. After a long run of studies, the only firm finding is that bibs grow larger as birds age.

  Juveniles resemble the adult female but are deeper brown below and paler above, with scruffier feathers. Their bills are light yellow to straw coloured. Plumage cannot reliably tell their sex, since some young males show no male markings and some young females show male features.

  On the scale, a sparrow weighs between 24 and 39.5 g, and a typical European bird weighs about 30 g. The body is compact, with a full chest, a large rounded head and a stout conical bill built for cracking seeds. Females are usually slightly smaller than males. Birds in colder climates and at higher latitudes tend to be larger, following a pattern known as Bergmann's rule.

  Listeners have transcribed the most common house sparrow sound as chirrup, tschilp or philip. Flocking or resting birds use it to keep in touch, and males use it to claim a nest and invite a mate. In the breeding season a male repeats it with speed and emphasis until it becomes something like a song. Young birds, especially in captivity, sometimes sing a warbling song resembling that of the European greenfinch.

  Aggression has its own sound, a trill written as chur-chur-r-r-it-it-it-it. Females use it in the breeding season to push males aside while they feed young or incubate eggs. A nasal quer warns of danger, and a shrill chree signals great distress. A soft quee, usually exchanged between a mated pair, calms tempers.

  The female's plumage is almost indistinguishable from that of females of the Spanish and Italian sparrows. That resemblance hides a tangled family history.

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• 3. Names and Kin

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  Carl Linnaeus described the house sparrow in 1758, in the 10th edition of Systema Naturae. That made it one of the first animals to receive a scientific name in the modern system of classification. His specimen came from Sweden, and he called it Fringilla domestica. The genus name Fringilla was later limited to the common chaffinch and its relatives. The sparrow moved to Passer, a genus created in 1760 by the French zoologist Mathurin Jacques Brisson.

  The two halves of the scientific name echo the English one. Passer, like the word sparrow, comes from a root referring to speed, and domesticus means belonging to the house. Local speech produced many nicknames, including spadger and spadgick in southern England, spug and spuggy in the north, and spur and sprig in Scotland. In North America the bird is often called the English sparrow, and spatzie comes from the German Spatz.

  The genus Passer holds about 25 species, or 26 by the Handbook of the Birds of the World. The house sparrow belongs to the Palaearctic black-bibbed sparrows and is a close relative of the Mediterranean willow sparrows. The best known of these is the Spanish sparrow. It often prefers wetter habitats and lives in nomadic colonies. In North Africa it hybridises with the house sparrow so extensively that populations range from pure house sparrows to pure Spanish sparrows.

  Most of Italy belongs to the Italian sparrow, which looks intermediate between the house and Spanish sparrows. Its origin is debated, and it may be a case of long-ago hybrid speciation. In the Alps it blends into the house sparrow across a strip roughly 20 km wide.

  Twelve subspecies are recognised, divided into two groups. The Palaearctic P. d. domesticus group has grey cheeks. The Oriental P. d. indicus group has white cheeks, a brighter crown, a smaller bill and a longer black bib. Many ornithologists in the 19th century treated indicus as a separate species.

  In the 1970s, birds of the subspecies bactrianus were recorded overlapping with domesticus birds without hybridising. The Soviet scientists Edward I. Gavrilov and M. N. Korelov therefore proposed making the indicus group its own species. Few accept the split, because the two groups blend across a large part of Iran.

  The subspecies bactrianus, described from Tashkent, is almost entirely migratory and winters on the plains of the northern Indian subcontinent. Across its range, the villages and towns belong to the Eurasian tree sparrow instead.

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• 4. Conquering the World

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  Roughly 10,000 years ago, according to what researchers believe, the house sparrow began its long association with people. The species originated in the Middle East and spread alongside agriculture across most of Eurasia and into parts of North Africa. From the mid-19th century, people carried it much further.

  In 1852, birds from England were released in New York City, in the hope that they would control the ravages of the linden moth. It was the first of many successful introductions to North America. Today the species ranges from the Northwest Territories of Canada to southern Panama, and it is among the most abundant birds of the continent.

  New Zealand received house sparrows in 1859, and from there they reached many Pacific islands, including Hawaii. Melbourne followed in 1863. Sparrows now thrive across eastern Australia as far north as Cape York. Western Australia has kept them out, and every house sparrow found in that state is killed.

  Around 1870, birds were introduced near Buenos Aires and quickly became common across the south of South America. They now occur almost continuously from Tierra del Fuego to the fringes of the Amazon basin. In the Falkland Islands the sparrows arrived as stowaways on whaling ships.

  Around 1900, southern Africa received both the European and the Indian subspecies. The European birds stayed confined to a few towns, but the Indian birds spread rapidly and reached Tanzania in the 1980s. Sparrows are thought to have reached Mombasa in Kenya around 1950. Not every attempt worked. Introductions to Greenland, the Bahamas and Cape Verde died out or had limited success.

  Where it takes hold, the house sparrow can extend its range at over 230 km per year. Its early adaptation to living with humans explains much of this success. It may also be able to suppress costly inflammatory and behavioural responses to immune challenges in its new range. The less successful invader, the Eurasian tree sparrow, seems to lack this ability. Even in northern Eurasia the sparrow has kept expanding since the 1850s, reaching Iceland and Rishiri Island in Japan around 1990.

  Despite its reputation as a companion of people, the bird is not strictly tied to them. Central Asian migrants usually breed in open country away from settlements. Dense forest and tundra are the only terrestrial habitats it avoids. In most of eastern Asia it is absent, replaced by the Eurasian tree sparrow. Where the two overlap, the house sparrow is usually commoner. One species may replace the other in a pattern the ornithologist Maud Doria Haviland described as "random, or even capricious".

  It prefers dry conditions, and it can tolerate high salt and survive without water by eating berries. Its densities are greatest in urban centres, and it is most abundant in wheat-growing regions such as the Midwestern United States. Its breeding success peaks in the suburbs, where insects are more plentiful than in city centres.

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• 5. Sociable Habits

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  In some places, supermarket doors open for house sparrows that have learned to trigger the automatic mechanism. The bird has also been seen clinging to hotel walls to watch vacationers on their balconies. In New Zealand it robs nectar from kowhai flowers. Such inventiveness suits an eater that takes whatever is available.

  Several studies in temperate farmland found that seeds make up about 90% of an adult's diet. Given a choice, it prefers cereals such as oats, wheat and maize. Town birds also eat bread, scavenge in garbage containers and gather outside restaurants for crumbs, though they favour raw seeds. Buds, berries, grapes and cherries are added, and in spring the bird has an unusual habit of tearing flowers, especially yellow ones.

  Animals fill out the menu. Beetles, caterpillars, flies and aphids are especially important, and the list extends to earthworms, molluscs, lizards and frogs. House sparrows have been seen stealing prey from American robins. Nestlings are fed mostly insects until about 15 days after hatching, and grasshoppers and crickets are the commonest items. Like many birds, sparrows also need grit to grind harder foods. Grains of masonry, egg shells and snail shells all serve, and oblong, rough grains are preferred.

  A house sparrow is gregarious whenever it feeds, often joining flocks of other species. Breeding nests are grouped in clumps, and the birds roost together. They bathe in dust or water in groups. They also practise what observers call social singing, in which several birds call together from a bush. At feeding stations and nests, females are dominant despite their smaller size.

  Captive sparrows have shown a strong ability to learn from each other. Individuals differ widely in how they react to a new object, food or place. Some approach and explore, while others keep away, a trait called neophobia. Captive birds changed their behaviour toward novel objects near their food dish after watching another bird. They did the same after hearing recorded sparrow calls.

  At dusk, communal chirping rises before and after the birds settle into the roost, and it starts again before they leave in the morning. Each bird sleeps with its bill tucked under the scapular feathers. In the laboratory, house sparrows show strong daily rhythms. Because they stay rhythmic even in constant darkness, they were among the first birds studied seriously for their circadian activity.

  Its flight is direct and flapping, averaging 45.5 km/h with about 15 wingbeats per second. On the ground it hops rather than walks. Pursued by a predator, it can swim, and captive birds have dived and swum short distances underwater.

  Most house sparrows never move more than a few kilometres in their lives.

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• 6. Family and Survival

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  A male house sparrow stakes his claim on a nest site before the breeding season, calling beside it again and again. When a female approaches, he bobs up and down, droops and shivers his wings, pushes up his head, spreads his tail and shows off his bib. She often responds with a threatening posture and an attack, then flies off with the male in pursuit. Other males join the chase and display to her too. Copulation is typically started by the female, with a soft dee-dee-dee call.

  The species is monogamous, and pairs typically mate for life. Yet about 15% of fledglings are unrelated to their mother's mate. Males guard their partners carefully, and most extra-pair mating happens away from the nest. Many birds never find a nest and a mate. Instead they act as helpers around mated pairs, which improves their chance of replacing a lost partner.

  Cavities are the preferred nest sites, most often the eaves and crevices of houses. Sparrows also use holes in cliffs and banks, tree hollows, and the abandoned nests of swallows. Sometimes they take over an active nest by driving off or killing its owners. In North America, the use of tree hollows puts sparrows in competition with bluebirds. In warmer places they build in the open, on evergreens and hawthorns or in the nests of large birds such as storks and magpies. Street lights and neon signs have been used for their warmth.

  The nest is usually domed, about 20 by 30 cm. It has an outer layer of stems and roots, a middle layer of dead grass and leaves, and a lining of feathers and paper. The unmated male begins it while displaying, and the female helps less. In colder regions the birds build special roost nests, or sleep in street lights, to keep warm in winter. The nests themselves shelter a wide range of scavenging insects, including over 1,400 species of beetle.

  A clutch usually holds four or five eggs, though counts from one to 10 have been recorded. Up to seven clutches a year may be laid in the tropics, or four in temperate latitudes. Central Asian sparrows, which migrate and raise only one clutch, average 6.5 eggs. The eggs are white, bluish white or greenish white, spotted with brown or grey, and average 2.9 g. The yolk makes up 25% of an egg, the white 68% and the shell 7%.

  The female develops a bare brood patch and does most of the incubating, spending the night on the eggs. The male can only cover them. The eggs hatch after 11 to 14 days. Chicks open their eyes after about 4 days and grow their first down at about 8 days. Both parents feed them, and in the first days the parents swallow the chicks' droppings. Later the droppings are carried up to 20 m from the nest. Young birds normally fledge after 14 to 16 days, and they feed themselves completely within 7 to 10 days. If both parents die, the loud begging of the chicks often draws in replacement parents.

  Survival is hard. Each year, 45-65% of adults survive, and only about 20-25% of hatchlings live to their first breeding season. The oldest known wild sparrow was found dead 19 years and 9 months after it was ringed in Denmark. The oldest captive bird lived for 23 years. Cats and birds of prey are the main predators. Accipiters and the merlin are especially important, though cats probably have a greater effect on populations. On European roads, the house sparrow is the bird most often found dead.

  Parasites and disease add to the toll. The ornithologist Ted R. Anderson listed thousands of them and noted that his list was incomplete. A comprehensive study found Salmonella in 13% of the sparrows tested, and outbreaks in spring and winter can kill large numbers. The bird carries avian pox and avian malaria, which it has spread to the native forest birds of Hawaii. West Nile virus survives temperate winters by going dormant in birds such as the house sparrow. Blood-feeding Dermanyssus mites from sparrow nests can enter homes and bite people, causing a condition called gamasoidosis.

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• 7. Pest and Symbol

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  From around 1560, northern Europeans hung earthenware sparrow pots from their eaves. Nesting birds moved in, and the young could be harvested easily. The practice lasted until at least the 19th century. Wild adults were netted in large numbers, and sparrow pie became a traditional dish. Because sparrows were associated with lechery, people believed the pie had aphrodisiac properties. A traditional Indian medicine called Ciṭṭukkuruvi lēkiyam, sold in Tamil, made similar claims. Sparrows were also trapped as food for falconers' birds and zoo animals.

  Persecution was constant. In Germany, sparrows were hunted from at least 1650 until 1970. During the 1870s, members of the House of Commons in England debated the damage sparrows did. Early in the 20th century, sparrow clubs culled many millions of birds and eggs, with only a local effect on numbers. Control methods have included trapping, poisoning and shooting adults, destroying nests and eggs, blocking nest holes, and scaring birds with noise, glue or porcupine wire. Large-scale control has failed. In most of the world the bird has no legal protection, and even birdwatchers often think little of it because it harasses other birds. Yet it also eats insect pests.

  People have nonetheless kept house sparrows as pets at many points in history. The bird has neither bright plumage nor an attractive song, and raising one is difficult.

  In European tradition, the sparrow stood for the common and vulgar, and for lust. Ancient Greeks linked sparrows with Aphrodite, the goddess of love, and later writers such as Chaucer and Shakespeare echoed the connection. Immigrants from Europe also valued the bird as a reminder of home, which was one reason for its introduction around the world. Ancient texts mention birds later called sparrows, though not always the house sparrow. Jesus's use of sparrows as an example of divine providence in the Gospel of Matthew inspired later references, including one in Shakespeare's Hamlet and the hymn His Eye Is on the Sparrow.

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• 8. Vanishing Sparrows

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  By 2021, a 21-year citizen science study found that house sparrow numbers in the bird's native Europe had fallen by nearly 60%. In Great Britain the population peaked in the early 1970s and has since dropped by 68% overall, and by about 90% in some regions. The RSPB lists the bird's UK conservation status as red. In London, the sparrow almost disappeared from the central city.

  The Netherlands has lost half its house sparrows since the 1980s, and the bird there is even considered endangered. That status drew wide attention after a female nicknamed the dominomus was killed. She had knocked down dominoes arranged for a world-record attempt. Bulgaria registered a 50% decrease as of 2023, though no serious declines had been reported from Eastern Europe by 2006.

  The losses were first noticed in North America, where they were first blamed on the spread of the house finch. Numbers there are estimated to have fallen by 84% since 1966. Declines have also appeared in Australia, where the sparrow arrived recently. In South Asia the bird has largely vanished from many major cities, and populations have dropped across many Asian countries, particularly India.

  The global picture is less grim. The IUCN estimates the world population at up to nearly 1.4 billion, which may place it second only to the red-billed quelea among wild birds. The quelea, unlike the sparrow, lives on a single continent and has never been introduced elsewhere. The IUCN lists the house sparrow as least concern. Earlier declines had also occurred in the 1920s, when the internal combustion engine replaced horses and a major source of food, spilled grain, disappeared.

  Researchers have proposed many causes. Predation by Eurasian sparrowhawks may play a part, possibly made easier by the removal of the bushes where sparrows hide. Other suspects include radiation from mobile phones and diseases such as avian malaria. Changes in urban building design have probably cut the supply of nest sites, and conservation groups encourage special nest boxes.

  The primary cause appears to be too little insect food for nestlings. Insect numbers fall with the spread of monoculture crops and heavy pesticide use. They also fall when native city plants give way to introduced species and parking areas. Another suspect is unleaded petrol, which produces toxic compounds such as methyl nitrite. Protecting insect habitats on farms, planting native species in cities and creating urban green spaces all help the sparrow.

  To raise awareness, World Sparrow Day has been celebrated on the 20th of March since 2010. In 2012 the house sparrow was declared the state bird of Delhi, to promote its conservation.

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