The British Trust for Ornithology
WILLOW WARBLER
Phylloscopus trochilus

Willow Warbler © Tommy Holden

Conservation listings

Unlisted/Green
Biodiversity Steering Group Conservation Concern List

Long-term trend
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, due to a fall in survival rates. However, this decline occurred only in the south of the UK (Peach et al. 1995) and Scottish populations remained unaffected. 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 productivity and an increase in nest failure rates at the chick stage (14 days) from 18% to 26%. Laying dates have become earlier which may 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
31
1968-1999 189 -40 -54 -23 >25  
 
25
1974-1999 195 -31 -46 -15 >25  
 
10
1989-1999 171 -24 -34 -14    
 
5
1994-1999 169 6 -2 15    
CBC farmland
31
1968-1999 78 -19 -37 1    
 
25
1974-1999 77 -9 -27 8    
 
10
1989-1999 74 -13 -26 -1    
 
5
1994-1999 73 19 7 32    
CBC woodland
31
1968-1999 76 -52 -69 -29 >50  
 
25
1974-1999 81 -41 -59 -18 >25  
 
10
1989-1999 79 -27 -41 -14 >25  
 
5
1994-1999 79 2 -8 12    
CES adults
15
1984-1999 92 -32 . . [>25*]  
 
10
1989-1999 106 -25 . . [>25*]  
 
5
1994-1999 111 -11 . .    
CES juveniles
15
1984-1999 90 -50 . . [>50*]  
 
10
1989-1999 105 -39 . . [>25*]  
 
5
1994-1999 112 -22 . .    
BBS UK
6
1994-2000 1224 13 8 18    
BBS England
6
1994-2000 863 -9 -13 -4    
BBS Scotland
6
1994-2000 176 40 22 60    
BBS Wales
6
1994-2000 130 -8 -19 3    
BBS N.Ireland
6
1994-2000 50 94 43 163   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 31 1968-1999 53 None        
Brood size 31 1968-1999 141 Curvilinear 5.23 chicks 5.39 chicks 0.16 chicks  
Daily failure rate (eggs) 31 1968-1999 73 None        
Daily failure rate (chicks) 31 1968-1999 129 Linear increase 0.0145 nests/day 0.0216 nests/day 0.0071 nests/day  
Laying date 31 1968-1999 91 Linear decline day 139 day 136 -3 days  
Percentage juveniles (CES) 15 1984-1999 98 Smoothed trend 150 productivity index 100 productivity index -33%[>25*]  
Percentage juveniles (CES) 10 1989-1999 113 Smoothed trend 128 productivity index 100 productivity index -22%  
Percentage juveniles (CES) 5 1994-1999 119 Smoothed trend 120 productivity index 100 productivity index -17%  
 




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This report should be cited as:
Baillie, S.R., Crick, H.Q.P., Balmer, D.E., Beaven, L.P., Downie, I.S., Freeman, S.N., Leech, D.I., Marchant, J.H.,
Noble, D.G., Raven, M.J., Simpkin, A.P., Thewlis, R.M. and Wernham, C.V.
(2002) Breeding Birds in the Wider
Countryside: their conservation status 2001. BTO Research Report No. 278. BTO, Thetford. (http://www.bto.org/birdtrends)

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