Contents of report
Breeding Bird Survey
Common Birds Census
Constant Effort Sites
Nest Record Scheme
Waterways Bird Survey
Alerts
Summary
What the categories mean
Return to BTO Home Page
.
TAWNY OWL Strix aluco
 
Conservation Listings Long term trend

Unlisted/Green
Biodiversity Steering Group Conservation Concern List

UK: Uncertain
 
Status Summary
As a nocturnal species, Tawny Owl is probably poorly covered by the CBC and the BBS. The non-significant long-term changes shown by both surveys may not, therefore, reflect real trends well. It may be notable that Gibbons et al. (1993) found evidence for a contraction of the species' UK range. The improvements in egg-stage nesting success could be linked to the declining impact of organochlorine pesticides. For the c.29-day egg stage, nest failure rates have fallen, on average, from 26% to 6%.
 
 
Table of population changes for Tawny Owl
Source Period
(yrs)
Years Plots
(n)
Change
(%)
Lower
limit
Upper
limit
Alert Comment
CBC all habitats 30 1968-1998 59 6 -24 48    
  25 1973-1998 63 -10 -31 16    
  10 1988-1998 60 1 -19 26    
  5 1993-1998 58 3 -11 23    
BBS UK 5 1994-1999 76 11 -17 49    
BBS England 5 1994-1999 63 29 -6 77    
The Breeding Bird Survey is jointly funded by BTO, JNCC and RSPB
 
 
Table of productivity information for Tawny Owl
Variable Period
(yrs)
Years Mean
annual
sample
Trend Predicted
in first year
Predicted
in last year
Change Comment
Clutch size 30 1968-1998 78 None        
Brood size 30 1968-1998 134 None        
Daily failure rate (eggs) 30 1968-1998 54 Linear decline 0.0101 nests/day 0.0023 nests/day -0.0078 nests/day  
Daily failure rate (chicks) 30 1968-1998 80 None        
Laying date 30 1968-1998 13 None       Small sample
 
Insufficient data on CES
available for this species
   




[ Welcome | Contents | Introduction | CBC | WBS | BBS | Heronries | CES | NRS | Alerts ]
[ Summary | Discussion | References | Help | BTO Home Page ]

© 2000 British Trust for Ornithology
BTO, The Nunnery, Thetford, Norfolk IP24 2PU
Tel: (+44) (0) 1842 750050 Fax: (+44) (0) 1842 750030 Email: info@bto.org

Last updated: 14 March, 2001

Page created by Susan Waghorn