Initial findings of Natural England's hen harrier tracking programme 2007 to 2014.
The hen harrier is one of England’s rarest and most spectacular birds of prey. On the continent these birds are found across a range of agricultural habitats, but in the UK their breeding range is currently confined primarily to heather moorland in the uplands, including Wales, northern England and Scotland.
Natural England is working on a range of fronts to further the conservation of this species. This includes:
- satellite tracking to improve our understanding of the bird’s movements and behaviour
- supporting wildlife friendly habitat management in the uplands
- working with a range of partners to develop a wider conservation strategy for hen harriers that looks to protect the current population and extend its range across England
Since 2007 Natural England has tagged 47 juvenile hen harriers in England, Scotland and the Isle of Man, and built up a detailed picture of their movements. An additional 6 birds have been tagged by Natural England and tracked by the RSPB as part of their Skydancer project. The RSPB were also given 2 tags to fit onto hen harriers in Argyllshire which they were also responsible for tracking.
We can now see in detail how some birds regularly travel hundreds of miles while others stick to much more confined geographical areas. Of the 47 birds Natural England has tracked, 4 are known to still be alive. 6 have been found dead and their bodies recovered and examined. There is evidence that infectious disease and/or predation have played a role in the deaths of 5 of them; 1 bird – Bowland Betty - was recovered last year and the Zoological Society of London (ZSL) indicated she had been shot. Signals from the tags fitted to the remaining 37 tagged hen harriers have ceased transmitting and the whereabouts of the birds are unknown. See table below giving summary of hen harriers satellite tagged since 2007.
Data from 2014
The results of this year’s tracking programme suggest the class of 2014 have experienced very mixed fortunes. This year Natural England tagged 9 hen harrier chicks at sites in the North West, the Peak District and Bowland Fells in England, and at Langholm in Scotland. 5 of these birds have been tracked as part of Natural England’s satellite tracking programme and 4 others (all from Bowland) as part of the RSPB’s Skydancer project.
Highlander and Burt from Bowland, and Annie from Langholm are alive and well and signals are still being actively transmitted.
Natural mortality rates in any year will be highest for recently fledged and inexperienced birds. This year, 2 of the young birds that Natural England were tracking (JoAnne from the north of England and NaTalie from the Peak District) are known to have died, probably from natural causes, although this is being investigated. Their bodies have been recovered and their remains have been examined by ZSL.
Satellite tags from an additional 4 birds are no longer sending out a signal and are subject to ongoing investigations.
2 of the missing birds are those the RSPB were tracking near Bowland (Sky and Hope). The RSPB hold the detailed tracking data and have confirmed that signals from the birds’ tags disappeared on 10 and 13 September 2014 respectively in close proximity to each other in the Bowland area.
Natural England was tracking Imogen (from a nest in northern England) and Sid (from a nest in Langholm, in Scotland). Signals from Imogen’s tag ceased on 1 September 2014 at a site in the Yorkshire Dales. Sid’s signal ceased transmitting on 21 September 2014 at a separate site in the Yorkshire Dales.
What do satellite transmitters tell us?
The satellite transmitters used on hen harriers are solar powered and transmit for about 10 hours before then undergoing a recharging period lasting around 48 hours (timelines are subject to a range of factors including prevailing light conditions).
In the case of Sid and Imogen, both signals had run their 10 hour course when last received and there is no indication of sudden signal interruption. It is quite possible, therefore, that the birds travelled some distance from their last recorded location (they have 48 hours to do so) and were either then lost en route, or for unexplained reasons, the tags never recharged. Sky’s case is unusual as the signal suddenly ceased quite early in the 10 hour transmission slot, suggesting an immediate and on-site interruption.
It is important to recognise that tracking data does not usually enable us to determine the circumstances that have led to loss of signal, nor what has happened to the bird. Tags normally operate for around 3 years and tag failure is uncommon but not unknown (we are aware of 3 instances since 2007 where birds were known to be alive but their tags were no longer transmitting). The fact that birds can travel up to 48 hours after their last signal also makes it very difficult to draw hard and fast conclusions about what may have happened to the birds when their signals cease transmission. Ultimately, only recovery of carcases and forensic analysis can establish that.
What you can do
In conjunction with local landowners and wildlife crime officers, Natural England have actively searched the last recorded location for the four birds that have recently gone missing, and to date have found nothing. The National Wildlife Crime Unit and local police have been informed. We are appealing for further information from local landowners and members of the public and anyone with any information is welcome to contact Crimestoppers on 0800 555 111 or their local police wildlife crime officer.
While Natural England is concerned for this year’s missing birds, there is more encouraging news from at least 2 of the birds tagged in 2013. The young females Hattie and Grainne successfully reared 8 chicks between them and both are still actively transmitting satellite signals.
Joint action plan for the recovery of the hen harrier in England
In a project led by Defra and involving a wider range of partners* we are working with moor owners, gamekeepers and conservation groups, to agree a shared plan to restore England’s hen harrier population. If agreement can be secured, this plan will promote breeding success across the uplands, re-establishment of the birds to the English lowlands and also help tackle wildlife crime, all aimed at encouraging sustainable growth of the hen harrier population. Natural England is firmly committed to this approach, and is working with all our partners to develop the plan in order to provide a more secure future for one of England’s most iconic breeding birds.
*The Hen Harrier Sub-Group includes Natural England, RSPB, GWCT, National Gamekeepers Organisation, National Parks UK and the Moorland Association
Tracking programme results
The full results of Natural England’s satellite tracking programme will be published as part of a PhD in 2015, but we are able to publish summary data for the birds tagged since 2007. This shows what we know about each bird’s status and grid reference (accurate to 100km2) of the last accurate transmission for the bird’s tag. In some instances, we are showing location only at a county level, following discussion with the relevant local raptor study groups, and concerns that providing a more accurate location could reveal sensitive roosting and breeding sites.
See Natural England’s web feature on the satellite tracking project.