30-12-2015 HOI AN, VIETNAM - EURASIAN TREE SPARROW (MALE) (Passer montanus)

The Eurasian tree sparrow (Passer montanus) is asmall passerine bird that breeds over most of temperate Eurasia and Southeast Asia, where it is known as the Tree sparrow. It 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 unrelated American tree 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 even within its genus in that it has no plumage differences between the sexes; the juvenile also resembles the adult, although the colors 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. Adult and juvenile Eurasian tree sparrows undergo a slow complete molt in the autumn and show an increase in body mass despite a reduction in stored fat. The change in mass is due to an increase in blood volume to support active feather growth and generally higher water content in the body.