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BTO Blueline
HEN HARRIER
Circus cyaneus

Hen Harrier © John Marchant
 

• Population
  changes

• Productivity
  trends

• Additional
  information
Conservation listings
Europe: SPEC category 3, vulnerable
UK: red (historical decline)
Long-term trend
UK: stable (between 1988–89 and 1998)
UK population size
570 (500–640) territorial pairs in 1998 (Sim et al. 2001: BiE04, APEP06); 806 (732–889) territorial pairs in 2004 (Sim et al. 2007a)
Status summary
Red listed because of substantial declines over the last two centuries, this species has suffered in recent decades from loss of habitat as forestry plantations have matured (Bibby & Etheridge 1993) but more especially from continuing illegal persecution on grouse moors (Etheridge et al. 1997). Although the Hen Harrier and other raptors have been protected under UK law since 1961, many are still killed unlawfully to protect Red Grouse stocks. The UK population was unchanged between surveys in 1988–89 and 1998, with declines in Orkney and England but increases in Northern Ireland and the Isle of Man (Sim et al. 2001). A decrease of 70% in the Orkney population over the last 20 years has been linked to reductions in the area of unmanaged grassland (Amar & Redpath 2005); the demographic drivers of this decline have been a decrease in polygyny and reduced nesting success among secondary females (Amar et al. 2005). The latest survey reveals a 41% increase in the UK and Isle of Man during 1998–2004, but with decreases in the Southern Uplands, east Highlands and England, all being areas with many managed grouse moors (Sim et al. 2007a). Although average clutch size declined substantially during the 1980s, further investigation has shown that this trend is due to the increased proportions in recent years of records from Orkney, where clutch sizes tend to be smaller than on the mainland (Summers 1998, Crick 1998). Recent results confirm that rough grass is a critical habitat for Orkney Hen Harriers, providing the necessary food during the incubation period (Amar et al. 2008).
 

Population changes
Annual breeding population changes for this species are not currently monitored by BTO
 

Productivity trends
Table of productivity changes for Hen Harrier

Variable Period
(yrs)		 Years Mean
annual
sample		 Trend Modelled
in first year		 Modelled
in 2006		 Change Comment
Clutch size 38 1968-2006 13 Curvilinear 5.48 eggs 4.73 eggs -13.6% Small sample
Brood size 38 1968-2006 20 None       Small sample
Daily failure rate (eggs) 38 1968-2006 11 Curvilinear 0.03% nests/day 0.22% nests/day 633.3% Small sample
Daily failure rate (chicks) 38 1968-2006 14 None       Small sample

Clutch size graph
Brood size graph
Egg nest failure graph
Chick nest failure graph

 

Insufficient data on laying date
available for this species

 

 

Insufficient data on CES
available for this species

 
 

Additional information
BTO blue divider
 

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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