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Northern Willow Warbler Moult Lasted About 15 Days

Juvenile willow warbler perched among branches
Research · Ecology

A field study in Russia’s far north found a highly concentrated moult in willow warblers (Phylloscopus trochilus) compared with reed buntings (Emberiza schoeniclus) at the same site. The study, published on 30 June 2026, used data collected at the Varlam Island research station in Pasvik State Nature Reserve, Murmansk Region, from 2022 to 2024.

Birds were captured in mist nets, examined alive and released. The researchers scored plumage condition in different feather tracts using standard methods, assessing post-juvenile moult in first-year birds and post-breeding flight-feather replacement in adults.

Willow warblers showed a synchronous and compressed pattern of feather replacement. Moult activity peaked from 6 to 11 August, and the estimated duration was about 15 days. Reed buntings showed a more prolonged pattern from 28 July to 29 August, lasting about 25–30 days and showing signs of two activity peaks.

The researchers also found characteristics associated with northern populations in both species: reduced moult completeness, earlier onset and partial overlap with the final stages of nesting. They linked the interspecific difference to migration strategy and feeding ecology. Reed buntings are short-distance migrants with a diet that includes seeds, whereas willow warblers are insect-eating long-distance migrants and replaced their plumage more rapidly as the polar summer waned.

The authors interpret these patterns as phenological adaptations to extreme northern conditions. They argue that the results add to understanding of how annual-cycle timing differs between migratory strategies and may help assess how northern birds respond to changing seasonal conditions.

Sources and image credit

  1. Slesareva, E. A., Melnikov, E. Y., Smolyakova, D. S., & Polikarpova, N. V. (2026). Patterns of post-juvenile and post-breeding molt of Reed Bunting (Schoeniclus schoeniclus) and Willow Warbler (Phylloscopus trochilus) at the Varlam Island Station (Murmansk region). Izvestiya of Saratov University. New Series. Series: Chemistry. Biology. Ecology, 26(2), 186–195. https://doi.org/10.18500/1816-9775-2026-26-2-186-195Primary research article published 30 June 2026 under CC BY 4.0. The 2022–2024 study at Varlam Island station in Pasvik State Nature Reserve compared post-juvenile and post-breeding moult in willow warblers and reed buntings under far-northern conditions.

Image: Stephan Sprinz / Wikimedia Commons — juvenile willow warbler (Phylloscopus trochilus) photographed at Spiekeroog, Lower Saxon Wadden Sea National Park, Germany, 15 June 2018; representative juvenile image, not a bird from the Russian study · CC BY-SA 4.0 · Source

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Ecology

SPECIES IN THIS STORY

Species in this story

Willow Warbler Phylloscopus trochilus Explore species Reed Bunting Emberiza schoeniclus Explore species

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