Eurasian Tree Sparrow (Passer montanus) lives in temperate forests across Europe, Asia, North Africa. It feeds on seeds and insects. Its conservation status is Least Concern.
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A real field recording of the Eurasian Tree Sparrow, made in the wild.
A single pair can raise two or three broods each year, each clutch holding five or six eggs that are only 20 mm × 14 mm and weigh 2.1 g, with the shell making up 7% of that weight. The eggs are incubated by both parents for 12-13 days before naked chicks hatch, and the fledglings leave the nest after a further 15-18 days. This rapid turnover lets the sparrow fit multiple breeding cycles into the long temperate summer, boosting its population potential despite a typical lifespan of just about two years.
In the United States the tree sparrow survives in a tiny 22,000 sq km (8,500 sq mi) pocket around St. Louis, where about 15,000 birds now live after being founded by just 20 individuals (or 12 pairs) released in late April 1870. This extreme bottleneck has left the American population with lower genetic diversity, which researchers think explains why its song structure differs from European birds and why it shows higher neophobia toward novel foods and objects.
A nest built in a wood-concrete box is 1.5 °C warmer than one in a plain wooden box, leading to a 76.5% occupancy rate versus 33.5% for the wooden version. Birds using the warmer boxes lay eggs earlier, have shorter incubation periods and attempt more broods each season, which translates into higher reproductive success. This shows how even modest changes in nest microclimate can dramatically improve breeding outcomes for cavity-nesting sparrows.
Tree sparrows are tiny: adults measure 12.5-14 cm (5-5½ in) long, span about 21 cm (8.3 in) across the wings and weigh just 24 g (0.85 oz), roughly 10% smaller than a house sparrow. Their small size, combined with a chestnut crown and a kidney-shaped black ear patch on pure white cheeks, makes them instantly recognizable even when juveniles look like duller adults. This compact build helps them slip into narrow tree holes and building crevices, the very sites they prefer for nesting.
Although the species is called a "tree" sparrow, it rarely lives high in the mountains; in Switzerland it only reaches 700 m (2,300 ft), yet it has been recorded breeding as high as 1,700 m (5,600 ft) in the northern Caucasus and a staggering 4,270 m (14,010 ft) in Nepal. This altitude flexibility lets the sparrow occupy a huge swath of temperate Eurasia, from sea-level coasts to alpine valleys, contributing to its status as Least Concern despite recent declines in western Europe.
Sources
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In the verdant tapestry of woodland edges and urban gardens, the Eurasian Tree Sparrow weaves a subtle yet vibrant thread, its chestnut cap and black throat patch a fleeting glimpse of beauty as it flits between branches. With a nimble flutter of its wings, this unassuming songster navigates the intricate network of twigs and leaves, its gentle chirping a soothing serenade to the natural world. As it forages for seeds and insects, its quiet industry belies a remarkable adaptability, thriving in a wide range of habitats from rural landscapes to bustling city streets.
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