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BTO Blueline
WILLOW WARBLER
Phylloscopus trochilus

Willow Warbler © Tommy Holden

 

• Population
  changes

• Productivity
  trends

• Additional
  information
Conservation listings
Europe: no SPEC category (favourable conservation status in Europe, not concentrated in Europe)
UK: amber (25–50% population decline)
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 apparently shown different trends at different UK latitudes. 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 has been moved from the green to the amber list. This decline occurred mainly in the south of the UK, 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 strong increase in Scotland and in Northern Ireland, and further 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 moderate decline in productivity as measured by CES and a substantial increase in failure rates at the egg stage. Laying dates have shifted earlier by a week, perhaps in response to recent climatic warming (Crick & Sparks 1999).
 

Population changes
CBC/BBS England graph
 
BBS acknowledgement
 
CES adult abundance
CES adult abundance
BBS UK graph
BBS England graph
BBS Scotland graph
BBS Wales graph
BBS N Ireland graph
 

Productivity trends
 
Clutch size graph
Brood size graph
Egg nest failure graph
Chick nest failure graph
Laying date graph
CES productivity graph
 

Additional information
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This report should be cited as:
Baillie, S.R., Marchant, J.H., Crick, H.Q.P., Noble, D.G., Balmer, D.E., Coombes, R.H.,
Downie, I.S., Freeman, S.N., Joys, A.C., Leech, D.I., Raven, M.J., Robinson, R.A. and Thewlis, R.M. (2006)
Breeding Birds in the Wider Countryside: their conservation status 2005.
BTO Research Report No. 435. BTO, Thetford. (http://www.bto.org/birdtrends)

Pages maintained by Susan Waghorn and Iain Downie: Last updated 2 May, 2006