Tree sparrow is known scientifically by the name of Passer montanus. These can be seen breeding over almost all the parts of Europe as well as Siberia. The allied forms of these birds can be seen in some regions of Asia. These birds were introduced to Australia as well as United States by the German immigrants during the 1870s. In the United States, these tree sparrows are known as German Sparrows or Eurasian Tree Sparrows for distinguishing them form the American Tree Sparrows, which are the natives of the US.
The Tree Sparrows have a length of about 12.4 cm to 14 cm. The crown as well as the nape of the adult sparrows possesses a rich chestnut colour. The ear-coverts and white cheeks of these sparrows possess one triangular patch which is black in colour. Even though, the chin as well as the throat of these sparrows is considered to be black, in reality these possess a colour which is dark grey in a richer shade. The brown wings of these birds possess two distinct but narrow bars of white colour across them.
The bill of the birds is of a lead-blue colour in summer where as during winter the colour of the bill turns into almost black. The legs possess a pale brown colour where are the irides of these birds are hazel in colour.
The young ones carry a very close resemblance of their parents, even while they are in the nests. The pattern of the face of the young sparrows is not so distinct. The young ones are normally dull. The belly and the breast of the young sparrows possess a browner shade than those of the parent sparrows.
The voice of these Tree sparrows are more shrill when compare to the voice of House Sparrows. The call of these birds is just one short chirp. The song which these sparrows sing consists of chirps that are modulated, but they are more musical.
The tree sparrows are very often confused with the House sparrows that are larger. But the rich brown head, which is almost coppery, the presence of black patch on their white cheeks as well as the wing bars which are white in colour give these birds a slighter as well as more graceful build. These features are the main characteristics of these sparrows.
Even though these birds belong to the rural European countries, these replace their relatives as town birds in the regions of Asia. These birds can be seen in the rural regions, towns as well as cities in Philippines. These are seen gathering as well as perching on the electric wires, especially during twilight.
These are gregarious birds in all the seasons. The groves present in old trees which contain numerous hollows or disused quarries are preferred by these sparrows to form the colonies. The holes are filled with grass, wool, hay or any other materials and then a lining with feathers is made which forms the nest of these sparrows.
The eggs are normally five in numbers, but it lays eggs between four and six. The eggs are usually small. In majority of the clutches, one of the eggs is lighter.