Eurasian tree sparrows have a typical lifespan of from 9 years and 10 months to 16 years and 5 months, with a maximum recorded lifespan of 13 years and 1 month, and a theoretical lifespan of from 9 years and 8 months to 13 years and 9 months; the species reaches sexual maturity from 8 months to 1 year and 1 month. An embryo develops inside an egg, receiving nutrients from the yolk, and the young’s eyes open from 4 to 5 days after hatching. The nestling stage involves the young being fed insects and seeds by its parents while in the nest, lasting from 2 weeks to 2 weeks and 6 days. Following this, the post-rapid growth phase sees the young bird learning to fly and forage independently, a period lasting from 2 weeks and 6 days to 10 months. The adult stage, during which the bird can reproduce and defend territory, lasts from 10 months to 8 years and 3 months.