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Phylloscopus trochilus

Willow Warbler © Tommy Holden


• Population

• Productivity

• Additional

Conservation listings
Europe: no SPEC category (favourable conservation status in Europe, not concentrated in Europe)
UK: amber (species level, 25–50% population decline; race trochilus, 25–50% population decline, European status)
Long-term trend
England: rapid decline
UK population size
2,125,000 territories in 2000 (1988–91 Atlas estimate updated using CBC/BBS trend: BiE04, APEP06)
Status summary
Willow Warbler abundance has shown regionally different trends within the UK (Morrison et al. 2010). The overall CBC/BBS trend shows a rapid decline during the 1980s and early 1990s, after 20 years of relative stability, and, on the strength of a 31% decline on CBC plots between 1974 and 1999, the species was moved from the green to the amber list. This decline occurred mainly in southern Britain, however, accompanied by a fall in survival rates there (Peach et al. 1995a), with Scottish populations remaining unaffected. BBS figures since 1994 indicate a stark contrast between an initially upward trend in Scotland and in Northern Ireland, and continued severe decreases in England and in Wales. Pressures on migration and in the winter are likely to be affecting the population, as is a reduction in habitat quality on the breeding grounds (Fuller et al. 2005). The recent population decline is associated with a shallow decline in productivity as measured by CES and with a substantial increase in failure rates at the egg stage, which raises NRS concern (Leech & Barimore 2008). There is a small but significant decrease in the number of fledglings per breeding attempt. Average laying dates have become a week earlier, perhaps in response to recent climatic warming (Crick & Sparks 1999). Numbers have shown widespread moderate decrease across Europe since 1980 (PECBMS 2010).
CBC/BBS England graph

1967-2008: -60% (confidence interval -70% to -45%)

Population changes in detail

 Demographic trends

Fledglings per breeding attempt graph

    1968-2008 decline from 3.48 to 3.01
fledglings per attempt
Laying date graph

          1968-2008 mean laying date advanced
     from 20 May to 13 May
More on demographic trends
Additional information

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This report should be cited as: Baillie, S.R., Marchant, J.H., Leech, D.I., Renwick, A.R., Joys, A.C., Noble, D.G., Barimore, C., Conway, G.J., Downie, I.S., Risely, K. & Robinson, R.A. (2010). Breeding Birds in the Wider Countryside: their conservation status 2010. BTO Research Report No. 565. BTO, Thetford. (http://www.bto.org/birdtrends)

Pages maintained by Iain Downie, Mandy T Andrews and Laura Smith: Last updated 25.01.2011