Eurasian Tree Sparrow

The Eurasian tree sparrow (Passer montanus) is a small species of sparrow found across much of Eurasia, with a length of about 12.5 to 14 cm (4.9-5.5 in) and a weight of 20-25 grams (0.70-0.88 oz). It is characterized by its chestnut brown head and nape, a distinctive black spot on each pure white cheek, and a black bib. The sexes are similar in appearance, which is unusual among sparrows. Its back is brown with black and white streaking, underparts are pale grey to brown. It is a social bird, often forming flocks outside the breeding season.

This bird is often confused with the house sparrow (Passer domesticus), but it can be differentiated by its smaller size, the chestnut head and black cheek spot, and its less robust build. No differences between sexes i also a differentiating factor between the species.

Natural habitats for the Eurasian tree sparrow include open woodlands, farmland, and around human habitations, particularly in rural and semi-urban areas. Unlike house sparrows, they are less common in dense urban environments. This species primarily feed on seeds, fruits, and insects. It exhibits flexibility in feeding habits, often foraging on the ground or taking advantage of bird feeders in urban areas. 

Breeding season for the Eurasian tree sparrow typically starts in April and can extend into August. They are monogamous and often reuse the same nesting site year after year. Nests are built in cavities, including tree holes, bird boxes, and even in buildings. The female lays 4-6 eggs per clutch, which are incubated for about 11-14 days. Both parents participate in feeding the altricial (helpless) chicks, which fledge approximately 18-20 days after hatching. They can have multiple broods in a single breeding season.

The Eurasian tree sparrow has been introduced to various parts of the world, including the United States, where it was released in St. Louis, Missouri, in the 1870s, and Australia, where it was first released in Victoria in the 1860s. These introductions have led to established populations, primarily in the American Midwest and southeastern Australia. The reasons for their introductions were similar to that of the house sparrow, aimed at controlling certain pests and as part of acclimatization efforts for European species.

In regions where Eurasian tree sparrows are introduced management efforts focus on monitoring their populations to prevent negative impacts on native species and ecosystems. Conservationists emphasize the importance of maintaining a balance between introduced and native species to ensure ecological harmony.

The Eurasian tree sparrow is a common species and has a very large distribution. It is not currently at significant risk of extinction. However, local populations may suffer from habitat loss and pollution, and it is believed that the total population number is decreasing. Conservation efforts are important to maintain stable population levels, especially in areas where they are considered a key part of the ecosystem. It is listed as least concern on the IUCN Red List.