The Eurasian Tree Sparrow (Passer montanus) is native to most of Europe and Asia. Although it was introduced to St. Louis, Missouri (U.S.A.), and Melbourne, Australia, in the 19th century, it has still not expanded beyond western Illinois and adjacent Missouri and Iowa in North America and southeastern Victoria and New South Wales in Australia, providing an example of a well established exotic species that is clearly not invasive (at least in its current ecological context). It is possible that the expansion of this species in both North America and Australia has been limited by the success of the House Sparrow (P. domesticus), both of these species having been introduced in both places around the same time (mid-late 19th century).

Eurasian Tree Sparrows feed mainly on grass and weed seeds, although some animal material is taken as well, especially during the breeding season, when nestlings are fed mainly insects and spiders. Eurasian Tree Sparrows typically breed in loose colonies. The domed nest is built by both sexes, usually in a natural or artificial cavity. Typical clutch size is 4 to 7 eggs. Incubation (for around two weeks) is by both parents. Nestlings are fed by both parents and remain in the nest around two weeks after hatching, although they may be fed by their parents for an additional week.

In various parts of the range, Eurasian Tree Sparrows may show minimal to substantial migratory movements. This species is very widespread and locally abundant. The estimated European population in the 1990s was around 15,000,000 breeding pairs. Although this species has continued to expand its global range, populations have experienced significant declines in some parts of the range, such as in Great Britain (although this species appears to have benefited somewhat from the decline of House Sparrows there, moving into farm buildings abandoned by them).

(Kaufman 1996; Summers-Smith 2009 and references therein)