Before You Blame a Grouse Moor: What 269 Tagged Hen Harriers Can and Can't Tell Us
- Rob Beeson
- Jun 9
- 5 min read
Updated: Jun 10
✅ Key Takeaway: A stopped hen harrier tag does not equal a moorland crime. Our open data on 269 birds demonstrates that natural mortality and technical failure frequently explain these disappearances.
When a tagged bird of prey goes missing in the uplands, some campaign material treats the disappearance as evidence of illegal killing by gamekeepers on grouse moors. But the tracking data doesn't support jumping to that conclusion.
The Moorland Association has compiled an open register of every satellite-tagged hen harrier tracked by Natural England and the Association since 2002 — 269 birds in total.
For each, we publish the tag serial number, tagging date and location, final transmission date and location, and recorded status. The full spreadsheet is downloadable here.
We are not asking anyone to take our word for any of it; we are asking them to check it.
What "Missing Fate Unknown" actually means
The "Missing Fate Unknown" (MFU) category is routinely read as a proxy for illegal killing. Natural England's own published notes do not support that reading.
NE records that MFU includes birds whose tags failed and birds that "died in such a position as to render the transmitter hard to locate and recover" — for example in dense vegetation where a solar panel cannot recharge.
MFU is a catch-all for technical and natural outcomes as well as suspicious ones. It is not a synonym for crime, and the published definition says so.
Tags fail for known reasons
The tags are not infallible, and their maker says as much. Microwave Telemetry Inc. lists harness failure, dirt or abrasion on the solar panel, deep vegetation blocking light, and proximity to large features such as cliffs among the causes of transmission loss.
A stopped signal is consistent with several outcomes. Treating it as proof of one creates false certainty.
Scale matters: 100 metres versus 40,000 hectares
Our register resolves final fixes to Ordnance Survey six-figure grid references — a 100-metre square. Several widely cited reports plot last-known locations within 10 km or 20 km squares.
A 20 km square covers 40,000 hectares (about 154 square miles). At that resolution a "final location" can implicate estates many miles from where a bird's tag actually fell silent.
Broad-scale mapping may be appropriate where sensitive wildlife locations need protection. But it is not appropriate for attributing responsibility. If a public map shows only a 10 km or 20 km square, that is too coarse to identify an estate, keeper, landholding or cause of death.
The RSPB's own "Satellite Tagged Hen Harrier Fates" map uses this broad-square method — visible, for instance, in its treatment of the bird named 'Sita'. The scale is too coarse to assign a fate to a property. We publish ours fine enough to be checked.
Natural mortality is high, and routinely left out
First-year mortality in hen harriers is substantial: only a minority of fledged chicks survive to their first birthday.
Any account that attributes a young bird's disappearance to human action without first weighing this is incomplete. The Yorkshire Dales report listed two harriers, aged 10 and 11 months, as MFU in 2024 without that context. It belongs in the record.
What our reclassification shows, and what it doesn't
We reclassified the fate data using a published, openly documented scheme, separating final fixes on land used for driven grouse shooting from those on other land or confirmed as natural causes.
The result is roughly even: of the birds with usable fate data, about 53% fell outside driven grouse moors or to natural causes, against about 47% on grouse-shooting land. Applied to the 58 birds in the Murgatroyd et al. (2019) dataset, our scheme produces a similarly even split rather than a strong skew.
We are clear about what this is and is not. It is the Moorland Association's analysis, not a peer-reviewed finding, and it rests on classification judgements that others may contest.
That is precisely why we publish the method and the raw data: so they can be contested. A claim that contradicts a peer-reviewed paper should be tested against peer review, not asserted over it. We invite that test.
Two data requests, two refusals
In July 2024 we asked the RSPB for the hen harrier tracking data behind its public reporting, and again for the data underlying the Ewing et al. paper. Both were declined.
On the first, the RSPB stated the data was "considered highly sensitive" and could not be released; on the second, that it wished to "maintain the integrity of our data."
We have published the full correspondence so readers can read the requests and responses in full and reach their own view. Natural England publishes precise location data for the birds it tracks; we think the case for releasing comparable data is strong, and we will keep asking.
Working with the official record
On 12 September 2025 we made a formal submission to the Yorkshire Dales Bird of Prey Partnership on its 2024 report, offering our analysis of the tagged birds and flagging three points:
the report's heavy reliance on RSPB data that is not independently verifiable
its use of the loaded term "persecution" in place of evidence-based language
its omission of high natural first-year mortality and of documented tag-failure causes for the birds it listed as missing.
We have also provided police units with a summary of the tracking evidence, to counter the assumption that a stopped tag automatically points to a moorland crime.
It records, among other patterns, a cluster of five final transmissions in the Kielder Forest area (no driven grouse shooting), five on the Isle of Man (no driven grouse shooting, fewer predators, yet tags still failed and birds were not recovered), and twelve birds whose final fixes lay well away from moorland — including the English Channel, the Spanish coast, and residential areas.
What we are asking for
A stopped tag tells you the data transmission stopped, nothing more. Before any disappearance is attributed to one cause, the record should account for the others the data plainly contains: a documented MFU definition that is not a crime statistic, known causes of tag failure, mapping precise enough to locate a bird rather than a region, and the high natural mortality of young birds.
Our data is downloadable. Our classification method is published. We are asking other holders of tracking data — the RSPB included — to do the same, so the question can be settled on a shared, verifiable evidence base rather than on whose dataset stays private.
The case for a central public register
This blog post illustrates exactly why there should be a single, central, public register of satellite-tagged hen harriers and other tagged raptors.
Recent online commentary elsewhere has raised questions about individual entries, but those questions actually reinforce the wider point: different organisations hold different parts of the evidence. Tag data, final transmission locations, recovery details, post-mortem results, police updates and the basis for conclusions are not consistently available in one place.
That is unsatisfactory for everyone. Proper scrutiny requires proper transparency.
A central register would allow all parties to scrutinise the same facts, reduce dispute, and improve confidence in the evidence. Subject to legitimate restrictions during live investigations, it should record the tag type, owner, fitting and final transmission details, recovery and post-mortem status, and the evidential basis for any conclusion.
If the aim is to understand what is happening to tagged birds, transparency is not a threat. It is the starting point. It is hard to see why anyone interested in the evidence would oppose that.
