Since 2007, Natural England tracked forty seven hen harriers, however the location of thirty seven of these hen harriers is not known. Four of the remaining ten are still alive, and it has been predicted that predation and disease killed five of the reaming birds and that one may have been shot illegally.
Natural England’s summary of the data they published could not conclude what happened to the missing thirty seven hen harriers, even the five which were tagged on the Isle of Man could not be located. The birds tagged in Bowland, Lancashire and at Langholm in Scotland went missing in areas other than that in which they were tagged, including Northern Ireland, Northern France, Lincolnshire, Shropshire and Dorset.
It has been stated that transmitter failure is a high explanation for the unaccounted for hen harriers, the batteries last for only three years. Natural England reported in 2007 three cases where hen harriers were seen still alive even though their transmitter stopped broadcasting.
Director of shooting for the Countryside Alliance, Adrian Blackmore stated: “It is clear from Natural England’s summary data that further research is required and we look forward to the publication of the full results next year”
“What can be said about the publication of this data is that it does not in any way substantiate unfounded allegations, made by the RSPB and others, of systematic persecution of hen harriers by grouse shooting interests”
“Any persecution of protected species is illegal and we absolutely condemn such killing, but the evidence of the tracking programme makes the claims made against grouse shooting unsustainable. Charities, in particular, have a duty to be factually accurate and we will hold them to that”
“This data also removes any barrier to the implementation of the hen harrier joint recovery plan. Hen harriers in England clearly need help and any further delay in publishing and delivering the plan is unacceptable”
• Satellite transmitters used on hen harriers are solar powered and transmit for around 10 hours before undergoing a recharging period lasting around 48 hours. Given that the grid reference of the last transmission for a bird’s tag is only accurate to 100Km2, and birds can travel 350 miles in a day with the result that birds could theoretically travel up to 700 miles after their last signal, it is impossible to draw hard and fast conclusions about where the birds may be, and what may have happened to them since their signals ceased – unless their bodies have been recovered and examined. Three of the missing birds are known to have been in France at the time.
• Natural mortality rates will be highest for recently fledged and inexperienced hen harriers. Of the 47 hen harriers tracked, 15 went missing between the ages of two months or less, with a further eight missing at the age of three months. Almost half of the birds being tracked by Natural England therefore went missing when natural mortality rates can be expected to be at their highest. Interestingly three hen harriers went missing within 10 days of having tags fitted – one on the same day. This could suggest a faulty batch of transmitters.
• It is clear from Natural England’s summary data that further research is required. The hen harrier is resident in some 87 countries across the northern hemisphere, and in a range of agricultural habitats. Although with a global population thought to be around 1,300,000, its numbers have never been high in Britain. As its name implies, it was in the past a predator of poultry, not many of which are now found on heather moorland in the uplands of the UK.
• On the continent hen harriers are found across a range of agricultural habitats, and given that 75% of the world’s remaining heather is found in the UK, the remaining 1,299,000 are not reliant on that as its natural habitat.
The Natural England report can be found here:
With many thanks to Natural England and the Countryside Alliance.
Anon. (2014). More questions than answers from Hen Harrier tracking data. Available: http://www.countryside-alliance.org/ca/campaigns-shooting/more-questions-than-answers-from-hen-harrier-tracking-data. Last accessed 16th Dec 2014.