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WILLOW WARBLER Phylloscopus trochilus
 
Conservation Listings Long term trend

Unlisted/Green
Biodiversity Steering Group
Conservation Concern List

UK: Moderate decline

 
Status Summary

Willow Warbler abundance has apparently shown very different trends around the UK. The national CBC trend shows a rapid decline in 1980s after 20 years of relative stability, but this decline occurred only in the south of the UK (Peach et al. 1995). The decline was driven by falling survival but Scottish populations were unaffected (Peach et al. 1995), and now, through the BBS, show evidence of further increases. The CBC and CES suggest that southern populations may have stabilised in the 1990s, but there is no evidence of a recovery as yet. The recent population decline is associated with a moderate decline in CES productivity and an increase in nest failure rates at the chick stage (14 days) from 18% to 27%. Laying dates have become earlier which can be explained by recent climate change (Crick & Sparks 1999).

 
 
Table of population changes for Willow Warbler
Source Period
(yrs)
Years Plots
(n)
Change
(%)
Lower
limit
Upper
limit
Alert Comment
CBC all habitats 30 1968-1998 190 -39 -52 -21 >25  
  25 1973-1998 194 -31 -44 -14 >25  
  10 1988-1998 172 -28 -38 -19 >25  
  5 1993-1998 168 6 -3 14    
CBC farmland 30 1968-1998 78 -21 . .    
  25 1973-1998 77 -12 . .    
  10 1988-1998 75 -21 . .    
  5 1993-1998 72 16 . .    
CBC woodland 30 1968-1998 76 -50 -70 -29 >50  
  25 1973-1998 80 -41 -62 -21 >25  
  10 1988-1998 78 -30 -48 -18 >25  
  5 1993-1998 78 4 -14 16    
CES adults 14 1984-1998 90 -31 . . [>25*]  
  10 1988-1998 103 -22 . .    
  5 1993-1998 110 -2 . .    
CES juveniles 14 1984-1998 89 -48 . . [>25*]  
  10 1988-1998 102 -37 . . [>25*]  
  5 1993-1998 111 -13 . .    
BBS UK 5 1994-1999 1201 14 9 19    
BBS England 5 1994-1999 852 -3 -8 2    
BBS Scotland 5 1994-1999 176 43 26 62    
BBS Wales 5 1994-1999 122 -4 -15 8    
BBS N.Ireland 5 1994-1999 46 68 19 138   Small sample
The Breeding Bird Survey is jointly funded by BTO, JNCC and RSPB
 
 
Table of productivity information for Willow Warbler
Variable Period
(yrs)
Years Mean
annual
sample
Trend Predicted
in first year
Predicted
in last year
Change Comment
Clutch size 30 1968-1998 54 None        
Brood size 30 1968-1998 142 Curvilinear 5.24 chicks 5.38 chicks 0.14 chicks  
Daily failure rate (eggs) 30 1968-1998 74 None        
Daily failure rate (chicks) 30 1968-1998 131 Linear increase 0.0143 nests/day 0.022 nests/day 0.0077 nests/day  
Laying date 30 1968-1998 92 Linear decline day 139 day 136 -3 days  
Percentage juveniles (CES) 14 1984-1998 96 Smoothed trend 156 productivity index 100 productivity index -36%[>25*]  
Percentage juveniles (CES) 10 1988-1998 109 Smoothed trend 130 productivity index 100 productivity index -23%  
Percentage juveniles (CES) 5 1993-1998 117 Smoothed trend 119 productivity index 100 productivity index -16%  
 
   




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Last updated: 15 March, 2001

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