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Song Thrush Fledging Success Ranged From 52% in Bushes to 78% in Urban Forests

Song thrush nest containing newly hatched chicks and a blue egg
Research · Reproduction & development

Hatching and fledging success of song thrush (Turdus philomelos) varied strongly among urban, suburban and peri-urban habitats around Stepanakert in Nagorno-Karabakh. A seven-year study published on 20 April 2026 found that the share of hatched chicks reaching fledging age was lowest in bush habitats, at 52.2%, and highest in urban forests, at 78.2%.

Researchers followed the nesting ecology of song thrushes from 2017 to 2023 in parks, gardens, orchards, cemeteries, shrub habitats and forests. They recorded 278 nests and 1,277 eggs in 269 nests, documenting nest placement, nesting plants, clutch characteristics and the fate of eggs and chicks.

Most eggs hatched, but fewer chicks reached fledging

Of the 1,277 eggs monitored, 1,119 hatched, corresponding to 87.6%. A total of 818 chicks reached fledging age, equivalent to 73.1% of hatched chicks and about 64% of all recorded eggs.

The share of eggs that hatched ranged from 78.5% in groves to 94.4% in urban forests. The authors interpret the higher reproductive success in less disturbed, structurally richer habitats as evidence that habitat structure and anthropogenic pressure influence breeding outcomes. They specifically suggest that the low fledging success in bush habitats may partly reflect nest height: nests there averaged about 1.5 metres above the ground, compared with about 4.3 metres in urban forests, potentially leaving eggs and chicks in low shrubs more exposed to predators.

Nests were concentrated on broadleaved trees

Of the 278 nests found, 172 — 61.9% — were placed in broadleaved trees. Another 43 were in conifers, 53 in broadleaved shrubs and 10 in coniferous shrubs. Nest height also differed clearly among habitats, reinforcing that the birds did not use the same nesting structure across the urban-to-peri-urban gradient.

Breeding extended over a long season, with the first reproductive phase beginning in early March and a second period around late May or early June. The researchers describe the species as behaviourally flexible across the urban-to-peri-urban gradient.

Sources and image credit

  1. Hayrapetyan, V. T., Grigoryan, N. M., Balayan, K. V., Balyan, L. V., & Aydinyan, L. G. (2026). The nesting ecology of song thrush (Turdus philomelos) in Stepanakert City of Nagorno-Karabakh and its adjoining areas. Ecological Questions, 37(2), 189–199.

Image: nottsexminer / Wikimedia Commons / Flickr. Song thrush nest with newly hatched chicks and an egg, England, 14 April 2012; illustrative photograph. · CC BY-SA 2.0 · Source

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