Eurasian Tree Sparrow

The Eurasian tree sparrow (Passer montanus) is a small passerine bird belonging to the Old World sparrow family, Passeridae. It is widely distributed across much of Europe and Asia and has also been successfully introduced to parts of North America and Southeast Asia. Recognised by its rich chestnut crown, distinctive black cheek patch, and neat black-and-white facial pattern, the species is notable for its ecological adaptability, social behaviour, and cultural significance, particularly in East Asia. Despite its extensive range and large global population, the Eurasian tree sparrow has experienced marked regional declines, especially in parts of western Europe.
The species is closely associated with open countryside, farmland, and lightly wooded habitats, contrasting with the house sparrow, which dominates more urbanised environments in Europe. Its biology, behaviour, and taxonomy have been studied extensively, making it a well-documented representative of the genus Passer.

Taxonomy and Nomenclature

The Eurasian tree sparrow was first scientifically described by Carl Linnaeus in 1758 in the 10th edition of Systema Naturae, under the name Fringilla montana. The original description referred to its dusky wings, grey and black body, and paired white wing bars. Like the house sparrow, it was initially placed among the finches (Fringillidae) but was later reassigned to the genus Passer by the French zoologist Mathurin Jacques Brisson in 1760, reflecting its closer affinities with Old World sparrows.
The binomial name Passer montanus is derived from Latin, with passer meaning “sparrow” and montanus meaning “of the mountains”. Both the scientific and English common names are somewhat misleading, as the species is not confined to mountainous or wooded habitats. In several European languages, alternative names such as the German Feldsperling and the Hungarian mezei veréb, both meaning “field sparrow”, more accurately describe its ecological preferences.
The Eurasian tree sparrow is not closely related to the American tree sparrow (Spizelloides arborea), which belongs to the New World sparrow family and differs significantly in morphology and evolutionary history.

Description and Identification

The Eurasian tree sparrow is a compact bird, typically measuring about 14 cm in length, with a wingspan of approximately 21–23 cm and an average weight of around 20–25 g. It is roughly ten per cent smaller than the house sparrow. One of its most distinctive features is the lack of sexual dimorphism: males and females are similarly plumaged, a characteristic that sets it apart from several other Passer species.
Adults have a rich chestnut crown and nape, contrasting with a clean white face marked by a kidney-shaped black patch on each cheek. The chin and throat form a small black bib, which is less extensive than that of the male house sparrow. The upperparts are light brown with black streaking, while the wings are brown with two narrow but clear white wing bars. The underparts are pale greyish-buff. Legs are pale brown, and the bill is lead-blue in summer, darkening to almost black in winter.
Juveniles closely resemble adults but have duller colours, reduced contrast in the facial pattern, and less defined markings. Both adults and juveniles undergo a complete moult in autumn. During this period, body mass increases despite a reduction in fat reserves, largely due to increased blood volume and water content supporting feather growth.

Vocalisations

Unlike many passerines, the Eurasian tree sparrow does not possess a true, melodious song. Its vocal repertoire consists mainly of short calls. These include an excited series of tschip notes given by unpaired or courting males, as well as simple chirps used in social interactions. The flight call is a harsh, metallic teck.
Studies of introduced populations in North America have shown that vocalisations can differ from those of European populations. Birds in Missouri, for example, exhibit fewer shared syllable types and more structured local variation, likely reflecting the limited genetic diversity of the small founding population.

Distribution and Habitat

The natural breeding range of the Eurasian tree sparrow spans most of temperate Europe and Asia, extending south of approximately 68° north latitude, beyond which summers are too cold to support breeding. Its range continues through central and eastern Asia and into Southeast Asia, reaching as far south as Java and Bali. Historically, the species also bred in areas such as the Faroe Islands, Malta, and Gozo.
The species is largely sedentary, although populations at the northern edge of the range may migrate southwards during winter. Small numbers also move from southern Europe into North Africa and the Middle East. In Asia, large seasonal movements occur, with thousands of birds passing through eastern China during autumn migration.
Preferred habitats include open farmland, grassland with scattered trees, orchards, hedgerows, and woodland edges. In Europe, the Eurasian tree sparrow is primarily associated with rural landscapes, while the house sparrow dominates urban areas. In contrast, in eastern Asia it is commonly found in towns and cities, often forming large urban populations.

Breeding Biology

The Eurasian tree sparrow is a social but monogamous breeder. Nesting occurs in loose colonies or isolated pairs, depending on habitat availability. The nest is characteristically untidy and bulky, constructed from grasses, straw, feathers, and other soft materials. Nest sites include natural tree cavities, holes in buildings, and the disused nests of larger birds such as European magpies or white storks.
Breeding typically begins in spring. A clutch usually consists of five or six eggs, though clutch size can vary. The eggs are incubated for less than two weeks, and both parents participate in feeding the nestlings. Invertebrates form an important part of the diet during the breeding season, providing essential protein for growing chicks.

Diet and Ecology

The Eurasian tree sparrow is primarily granivorous, feeding on seeds from grasses, cereals, and weeds. Invertebrates, including insects and spiders, are also consumed, particularly during the breeding season. This flexible diet contributes to the species’ ability to exploit a wide range of habitats.
Like other small birds, it is subject to predation by birds of prey and suffers mortality from parasites and disease. The average lifespan is relatively short, typically around two years, although some individuals live longer under favourable conditions.

Subspecies Variation

Although the Eurasian tree sparrow occupies an enormous geographical range, it shows relatively little variation in appearance. Seven subspecies are generally recognised, differing only subtly in size, colour tone, and intensity of markings. These include the nominate European subspecies (P. m. montanus), as well as regional forms such as P. m. dilutus of Central and South Asia, P. m. tibetanus of the Himalayas, and P. m. saturatus of East Asia and Japan. Numerous additional subspecies names have been proposed historically but are now regarded as intermediate forms.