Guest blog: What happened to the 58 Hen Harriers? The unanswered questions behind Natural England’s brood management experiment

This is a guest blog by Mike Whitehouse.

WHAT HAPPENED TO THE 58 HEN HARRIERS? THE UNANSWERED QUESTIONS BEHIND NATURAL ENGLAND’S BROOD-MANAGEMENT EXPERIMENT

I have followed the fortunes of Hen Harriers for many years. My concern is straightforward. I wanted my children to be able to see these magnificent birds flying over the northern uplands as a normal part of our wildlife, not as a rare and precarious privilege.

That is why I have taken a particular interest in Natural England’s Hen Harrier Brood Management Trial.

The trial has now finished. The licence period ran from 2018 to 2024, with brood management actually taking place between 2019 and 2023. Natural England published its final evaluation in July 2026.

But there remains one rather obvious question.

What happened to the birds?

58 birds were released

During the trial, 59 chicks were taken into captivity and 58 were eventually released.

Of those 58 released birds:

• 39 were fitted with satellite tags
• 19 were released without satellite tags

The satellite tags were intended to provide a means of monitoring survival and, where a bird died or disappeared, potentially investigating what had happened.

Indeed, Natural England explained the theory behind the trial quite clearly. If brood management reduced conflict with grouse shooting interests, this should lead to reduced persecution, improved survival and ultimately more Hen Harriers breeding in the wild.

So the fate of those released birds is rather important.

What happened to the 39 tagged birds?

The final evaluation contains the status of the satellite-tagged brood-managed birds at the end of the trial.

At the December 2024 endpoint, three were still alive and actively being tracked.

For the other 36 tagged birds, there was no current evidence of survival from the satellite tracking data.

That statement needs some careful qualification.

According to RPUK two of those 36 birds had in fact already been found dead and have been included in their running tally of 149 missing/killed Hen Harriers.

They were:

• R2-F2-20, brood-managed in 2020
• R3-F1-22, brood-managed in 2022

Both birds had spent the winter of 2022 at the same North Pennines roost.

This distinction matters because the deaths were not discovered after the trial. What happened after the trial was that Natural England finally published the details, on 18 December 2024, after the relevant police investigations had concluded.

Two birds found with shotgun pellets

The post-mortem examinations found three suspected lead shotgun pellets in R2-F2-20 and two suspected lead shotgun pellets in R3-F1-22.

Natural England nevertheless said that their presence suggested ongoing illegal persecution of Hen Harriers in northern England.

And what about the other 34 tagged birds?

This is where the numbers need to be handled carefully.

The 39 tagged birds comprise:

3 alive and actively tracked at the end of the trial

Plus

36 for which the tracking record provided no current evidence of survival at the December 2024 endpoint.

Two of those 36 had subsequently been recovered dead, with shotgun pellets in their bodies.

That leaves 34 tagged birds for which there is no documented evidence of subsequent survival.

Then in addition, there are also the 19 birds which were released without satellite tags.

Natural England has told me that it believes all the brood-managed birds were ringed and that the ringing records were shared with the British Trust for Ornithology.

But Natural England’s Hen Harrier Team has told me that it holds no record of the fates of the brood-managed birds that were not fitted with satellite tags. That leaves an important information gap.

A summary of the 58 birds released:

• 3 were alive and actively satellite-tagged at the end of the trial
• 2 were subsequently confirmed dead, both with shotgun pellets in their bodies
• 34 tagged birds have no documented evidence of subsequent survival
• 19 untagged birds have no fate record held by Natural England

In other words, 53 of the 58 released birds currently have no documented evidence of subsequent survival. That does not mean that 53 birds are known to have died. It does mean that, on the information currently available, there is no documented evidence establishing that they survived.

That is an important distinction.

Did brood management actually increase the Hen Harrier population?

This is perhaps the most interesting part of Natural England’s final evaluation.

The answer is not simply that 58 captive-reared birds caused the subsequent increase in Hen Harrier numbers.

Natural England itself says the number of brood-managed chicks was far too small to explain the substantial increase in nesting pairs.

The population modelling commissioned from the British Trust for Ornithology indicated that the increase was more consistent with higher survival and greater settlement and breeding by wild birds.

Natural England nevertheless concluded that the availability of brood management probably contributed to population growth, particularly through increased breeding on some grouse moors.

But there is an important qualification.

Natural England acknowledges that the effects of brood management could not be completely separated from the satellite tagging, monitoring and surveillance programme that accompanied it.

That makes the question of what actually drove the recovery more complicated than simply saying that brood management worked.

And what about persecution?

Natural England’s own conclusion is also quite clear on this point.

Illegal killing continued throughout the trial.

The final evaluation says that illegal killing remains a significant constraint on Hen Harrier recovery and that the trial did not demonstrate a widespread reduction in illegal killing.

That is particularly relevant when considering the fate of the brood-managed birds.

What did the experiment actually cost?

This is another area where the full picture is not yet available.

It said that Hen Harrier monitoring and recovery work overall had been estimated at hundreds of thousands of pounds annually, involving several directorates, but that it did not hold a detailed breakdown of their work.

Following an Environmental Information Regulations request, Natural England disclosed £83,613.50 of identifiable external expenditure associated with the work I asked about.

That included:

• £3,291.50 for satellite-tag data extraction in 2022
• £49,999 for the 2024 National Centre for Social Research study
• £30,323 for the British Trust for Ornithology population modelling

Natural England also said that two of the reports were produced internally and therefore did not have separately identifiable external costs.

However, Natural England did not provide a complete internal staff-cost figure for the trial.

There are also questions about the satellite tags themselves. Six reconditioned tags were supplied in 2023 but no costs were shown* against the remaining 33 tags or for the cost of their transmissions and associated data services.

So £83,613.50 cannot be presented as the total cost of their brood-management experiment. It is just the identifiable external expenditure Natural England has so far disclosed. I have therefore asked Natural England for further clarification.

What did Natural England actually learn from this financially costly experiment that displaced these birds, raised them in captivity and released them back into a predatory environment, where the majority of them were likely to be never seen again?

The unanswered question

Natural England has now concluded that the brood-management trial contributed to an increase in Hen Harrier nesting on some grouse moors.

It also accepts that the numbers of captive-reared birds were too small to explain the overall increase in wild bird survival and that the effects of brood management cannot be completely separated from the intensive tagging and monitoring programme, and that illegal killing continued throughout the trial.

Against that background, I keep coming back to the birds themselves.

58 were released.

39 were satellite tagged.

3 were still alive and actively tracked at the end of the trial.

Two others had already been found dead, both with shotgun pellets in their bodies.

34 tagged birds have no documented evidence of subsequent survival.

19 released without satellite tags for which Natural England says it holds no fate records.

That is a remarkable amount of uncertainty surrounding the fate of birds that were deliberately taken from the wild, raised in captivity and released as part of a scientific experiment.

The obvious next step is surely to find out what can still be established.

Were any of the 19 untagged birds subsequently seen?

Were any identified through their rings?

Does the BTO hold records that Natural England does not?

And, more broadly, what happened to the birds once the experiment stopped?

I have therefore approached the relevant organisations for any additional records they may hold.

Because ultimately, whatever one’s view of brood management, these were not numbers on a spreadsheet. They were 58 individual Hen Harriers and we should be able to account for what happened to them. They represent a significant cohort of Hen Harriers in England.

Natural England itself says that illegal killing continued during the trial and remains a significant constraint on Hen Harrier recovery.

So if persecution remains a problem, should conservation policy concentrate on finding ways of making Hen Harriers more acceptable to grouse shooting interests?

Or should it concentrate much more heavily on ensuring that a protected bird is actually protected?

That is not an argument against every grouse moor manager. There are undoubtedly estates and individuals who genuinely support Hen Harrier conservation.

But the continuing disappearance of protected birds means that the question cannot simply be ignored. I started campaigning because I wanted to see Hen Harriers flying over the northern uplands as a normal part of our wildlife not as a rare and precarious privilege.

ENDS

*Ed: it’s my understanding that the Moorland Association paid for the costs of the satellite tags used during the trial. It’s also my understanding that the Moorland Association paid the brood meddling licence holder, Jemima Parry Jones of the International Centre for Birds of Prey, for the costs of the removal of HH chicks from the moors, the costs of holding them and rearing in captivity, and the costs of their subsequent release.