The tree sparrow (Passer montanus ) is a passerine bird in the sparrow family with a rich chestnut crown and nape and a black patch on each pure white cheek. The sexes have similar plumage, and young birds are duller versions of the adult. This sparrow breeds across much of temperate Eurasia and Southeast Asia and has been introduced elsewhere, including the United States, where it is known as the Eurasian tree sparrow or German sparrow to differentiate it from the native American tree sparrow. Although several subspecies are recognised, the appearance of this bird varies little across its extensive range.
The untidy nest of the tree sparrow is built in a natural cavity, a hole in a building, or the disused nest of a European magpie or white stork. The typical clutch is five or six eggs, which hatch in under two weeks. This sparrow mainly feeds on seeds, but also consumes invertebrates, particularly during the breeding season. As with other small birds, infection by parasites and diseases, as well as predation by birds of prey, take their toll, and the typical lifespan is about two years.
The tree sparrow is widespread in the towns and cities of eastern Asia, but in Europe, it inhabits lightly wooded open countryside, while the house sparrow breeds in more urban areas. The tree sparrow's extensive range and large population mean it is not globally endangered, although there have been significant population declines in Western Europe, partly due to changes in farming practices involving increased use of herbicides and the loss of winter stubble fields. In eastern Asia and western Australia, this species is sometimes considered a pest, though it is also widely celebrated in oriental art.
Description The tree sparrow is long, with a wingspan of about and a weight of , making it roughly 10% smaller than the house sparrow. The adult's crown and nape are rich chestnut, and there is a kidney-shaped black ear patch on each pure white cheek; the chin, throat, and the area between the bill and throat are black. The upperparts are light brown, streaked with black, and the brown wings have two distinct narrow white bars. The legs are pale brown, and the bill is lead-blue in summer, becoming almost black in winter.
This sparrow is distinctive within its genus because there are no plumage differences between the sexes. Juveniles also resemble adults, although their colours tend to be duller. Its contrasting face pattern makes this species easily identifiable in all plumages; the smaller size and brown, not grey, crown are additional differences from the male house sparrow. Both adult and juvenile tree sparrows undergo a slow, complete moult in autumn and experience an increase in body mass, despite a reduction in stored fat. This change in mass is due to an increase in blood volume to support active feather growth, as well as a higher overall body water content.
The tree sparrow does not have a true song, but its vocalisations include an excited series of tschip calls made by unpaired or courting males. Other monosyllabic chirps are used for social interaction, and the flight call is a harsh teck. A study comparing the vocalisations of the introduced Missouri population with those of birds from Germany showed that the US birds had fewer shared syllable types (memes) and more structure within the population than the European sparrows. This may be due to the small size of the original North American population, resulting in a loss of genetic diversity.
Taxonomy
The Old World sparrow genus Passer is a group of small passerine birds that is believed to have originated in Africa, and which contains 15–25 species depending on the authority. Its members are typically found in open, lightly wooded, habitats, although several species, notably the house sparrow (P. domesticus) have adapted to human habitations. Most species in the genus are typically long, predominantly brown or greyish birds with short square tails and stubby conical beaks. They are primarily ground-feeding seed-eaters, although they also consume invertebrates, especially when breeding. The Eurasian species is not closely related to the American tree sparrow (Spizelloides arborea), which is in a different family, the New World sparrows.
The tree sparrow's binomial name is derived from two Latin words: passer, "sparrow", and montanus, "of the mountains" (from mons "mountain"). The tree sparrow was first described by Carl Linnaeus in his 1758 Systema Naturae as Fringilla montana, F. remigibus rectricibusque fuscis, corpore griseo nigroque, alarum fascia alba gemina but, along with the house sparrow, it was soon moved from the finches (family Fringillidae) into the new genus Passer created by French zoologist Mathurin Jacques Brisson in 1760. The tree sparrow's common name is given because it prefers tree holes for nesting. This name, and the scientific name montanus, do not appropriately describe this species's habitat preferences: the German name Feldsperling and the Hungarian name mezei veréb ("field sparrow") comes closer to doing so.
Subspecies
This species varies little in appearance across its large range, and the differences between the seven extant subspecies recognised by Clement are slight. At least 15 other subspecies have been proposed, but these are considered intermediates of the recognised subspecies. The European tree sparrow (P. m. montanus), the nominate subspecies, ranges across Europe except for the southwestern Iberian Peninsula, southern Greece and the former Yugoslavia. It also breeds in Asia east to the Lena River and south to the northern regions of Turkey, the Caucasus, Kazakhstan and Mongolia and in North Korea. The Caucasian tree sparrow (P. m. transcaucasicus), described by Sergei Aleksandrovich Buturlin in 1906, breeds from the southern regions of the Caucasus east to northern Iran. It is duller and greyer than the nominate subspecies. The Afghan tree sparrow (P. m. dilutus), described by Charles Wallace Richmond in 1856, is resident in extreme northeastern Iran, northern Pakistan and northwestern India. It also occurs further north, from Uzbekistan and Tajikistan east to China. Compared to P. m. montanus, it is paler, with sandy-brown upperparts. The Tibetan tree sparrow (P. m. tibetanus), the largest subspecies by size, was described by Stuart Baker in 1925. It is found in the northern Himalayas, from Nepal east through Tibet to northwestern China. It resembles P. m. dilutus, but is darker. P. m. saturatus, described by Leonhard Hess Stejneger in 1885, breeds in Sakhalin, the Kuril Islands, Japan, Taiwan and South Korea. It is deeper brown than the nominate subspecies and has a larger bill. P. m. malaccensis, described by Alphonse Dubois in 1885, is found from the southern Himalayas east to Hainan and Indonesia. It is a dark-coloured subspecies, like P. m. saturatus, but is smaller and more heavily streaked on its upperparts. P. m. hepaticus, described by Sidney Dillon Ripley in 1948, breeds from northeastern Assam to northwestern Burma. It is similar in appearance to P. m. saturatus, but redder on its head and upperparts.
Distribution and habitat
The tree sparrow's natural breeding range comprises most of temperate Europe and Asia south of about latitude 68°N (north of this the summers are too cold, with July average temperatures below ) and through Southeast Asia to Java and Bali. It formerly bred in the Faroes, Malta and Gozo. In South Asia it is found mainly in the temperate zone. It is sedentary over most of its extensive range, but northernmost breeding populations migrate south for the winter, and small numbers leave southern Europe for North Africa and the Middle East. The eastern subspecies P. m. dilutus reaches coastal Pakistan in winter and thousands of birds of this race move through eastern China in autumn.
The tree sparrow has been introduced outside its native range but has not always become established, possibly due to competition with the house sparrow. It was introduced successfully to Sardinia, eastern Indonesia, the Philippines and Micronesia, but introductions to New Zealand and Bermuda did not take root. Ship-carried birds colonised Borneo. This sparrow has occurred as a natural vagrant to Gibraltar, Tunisia, Algeria, Egypt, Israel, the United Arab Emirates, Morocco and Iceland. In North America, a population of about 15,000 birds has become established around St. Louis and neighbouring parts of Illinois and southeastern Iowa. These sparrows are descended from 20 birds (or 12 pairs, depending on the source) imported from Germany and released in late April 1870, probably by members of an acclimatisation society.
Within its limited US range of about , the tree sparrow has to compete with the house sparrow in urban centres, and is therefore mainly found in parks, farms and rural woods. It has been suggested that one factor limiting the spread of tree sparrows in North America is the species' higher neophobia (novelty aversion) compared to house sparrows; one study specifically found that captive tree sparrows showed lower willingness to eat novel foods and habituated more slowly to novel objects than house sparrows. The American population is sometimes referred to as the "German sparrow", to distinguish it from both the native American tree sparrow species and the much more widespread "English" house sparrow. American birds have developed differences in size, genetics, and song from Old World populations as a result of prolonged isolation.
In Australia, the tree sparrow is present in Melbourne, towns in central and northern Victoria and some centres in the Riverina region of New South Wales. It is a prohibited species in Western Australia, where it often arrives on ships from Southeast Asia.
Despite its scientific name, Passer montanus, this is not typically a mountain species, and only reaches in Switzerland, although it has bred at in the northern Caucasus and as high as in Nepal. In Europe, it is frequently found on coasts with cliffs, in empty buildings, in pollarded willows along slow water courses, or in open countryside with small isolated patches of woodland. The tree sparrow shows a strong preference for nest-sites near wetland habitats and avoids breeding on intensively managed mixed farmland.
When the tree sparrow and the larger house sparrow are found in the same area, the house sparrow usually breeds in urban areas, while the smaller tree sparrow nests in the countryside. Where trees are scarce, as in Mongolia, both species may use man-made structures for nesting. The tree sparrow is a rural bird in Europe, but is an urban bird in eastern Asia. In southern and central Asia, both species of the genus Passer may be found around towns and villages. In parts of the Mediterranean, such as Italy, both the tree and the Italian or Spanish sparrows may be found in settlements. In Australia, the tree sparrow is largely an urban bird, whereas the house sparrow uses more natural habitats.
Behaviour and ecology
Breeding
The tree sparrow reaches breeding maturity within a year of hatching, and typically builds its nest in a cavity in an old tree or rock face. Some nests are not situated in holes per se, but are built among roots of overhanging gorse or similar bushes. Roof cavities in houses may also be used. In the tropics, the crown of a palm tree or the ceiling of a veranda may serve as a nest site. This species will breed in the disused domed nest of a European magpie, or an active or unused stick nest of a large bird such as the white stork, white-tailed eagle, osprey, black kite or grey heron. It will sometimes attempt to take over the nest of other birds that breed in holes or enclosed spaces, such as the barn swallow, house martin, sand martin or European bee-eater.