The Eurasian Tree Sparrow, Passer montanus, is a passerine bird in the sparrow family with a rich chestnut crown and nape, and a black patch on each pure white cheek. The sexes are similarly plumaged, and young birds are a duller version of the adult. This sparrow breeds over most of temperate Eurasia and Southeast Asia, where it is known as the Tree Sparrow, and 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.
Pairs may breed in isolation or in loose colonies and will readily use nest boxes. In a Spanish study, boxes made from a mixture of wood and concrete (woodcrete) had a much higher occupancy rate than wooden boxes (76.5% versus 33.5%), and birds nesting in woodcrete sites had earlier clutches, a shorter incubation period and more breeding attempts per season. Clutch size and chick condition did not differ between nest box types, but reproductive success was higher in woodcrete, perhaps because the synthetic nests were 1.5 °C warmer than their wooden counterparts.
The immune response of Tree Sparrows is less robust than that of the House Sparrow and has been proposed as a factor in the greater invasive potential of the latter.The House Sparrows and Tree Sparrow are the most frequent victims of roadkill on the roads of Central, Eastern and Southern Europe. The maximum recorded age is 13.1 years but three years is a typical lifespan.