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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 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 moderate 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). Average laying dates have become a week earlier, perhaps in response to recent climatic warming (Crick & Sparks 1999). Numbers have fallen widely in Europe since 1980 (PECBMS 2007).
 

Population changes
CBC/BBS England graph
 
Table of population changes for Willow Warbler

Source Period
(yrs)		 Years Plots
(n)		 Change
(%)		 Lower
limit		 Upper
limit		 Alert Comment
CBC/BBS England 39 1967-2006 399 -58 -70 -46 >50  
  25 1981-2006 532 -58 -67 -49 >50  
  10 1996-2006 938 -30 -36 -24 >25  
  5 2001-2006 820 -11 -18 -7    
CES adults 22 1984-2006 88 -61 -70 -52 >50  
  10 1996-2006 91 -48 -54 -42 >25  
  5 2001-2006 77 -7 -14 1    
CES juveniles 22 1984-2006 89 -72 -78 -63 >50  
  10 1996-2006 98 -53 -62 -45 >50  
  5 2001-2006 86 -10 -19 1    
BBS UK 11 1995-2006 1275 -14 -20 -7    
  10 1996-2006 1293 -17 -23 -10    
  5 2001-2006 1260 -8 -13 -5    
BBS England 11 1995-2006 866 -32 -37 -27 >25  
  10 1996-2006 873 -31 -36 -26 >25  
  5 2001-2006 820 -12 -18 -9    
BBS Scotland 11 1995-2006 182 5 -10 16    
  10 1996-2006 183 -5 -18 5    
  5 2001-2006 180 -7 -14 -1    
BBS Wales 11 1995-2006 152 -27 -37 -14 >25  
  10 1996-2006 157 -26 -36 -14 >25  
  5 2001-2006 170 -11 -19 -5    
BBS N.Ireland 11 1995-2006 70 36 5 56    
  10 1996-2006 76 12 -9 25    
  5 2001-2006 86 -4 -16 8    

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
Table of productivity changes for Willow Warbler

Variable Period
(yrs)		 Years Mean
annual
sample		 Trend Modelled
in first year		 Modelled
in 2006		 Change Comment
Clutch size 38 1968-2006 49 None        
Brood size 38 1968-2006 131 None        
Daily failure rate (eggs) 38 1968-2006 69 Linear increase 0.93% nests/day 1.66% nests/day 78.5%  
Daily failure rate (chicks) 38 1968-2006 120 None        
Laying date 38 1968-2006 84 Linear decline May 20 May 14 -6 days  
Juvenile to Adult ratio (CES) 22 1984-2006 95 Smoothed trend 144 Index value 100 Index value -31% >25  
Juvenile to Adult ratio (CES) 10 1996-2006 103 Smoothed trend 112 Index value 100 Index value -11%  
Juvenile to Adult ratio (CES) 5 2001-2006 90 Smoothed trend 109 Index value 100 Index value -8%  

 
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., Leech, D.I., Joys, A.C., Noble, D.G.,
Barimore, C., Grantham, M.J., Risely, K. & Robinson, R.A. (2009).
Breeding Birds in the Wider Countryside: their conservation status 2008.
BTO Research Report No. 516. BTO, Thetford. (http://www.bto.org/birdtrends)

Pages maintained by Iain Downie, Mandy T Andrews and Laura Smith: Last updated 18.02.2009