The experimental trial of hen harrier ‘brood management’ has ended, concluding that this activity has contributed to increased numbers of nesting hen harriers on some grouse moors. However, illegal killing of hen harriers has continued, and a range of approaches may continue to be required to maintain and build on the progress we have seen in recent years.
Hen harriers are rare birds of prey, and their numbers have long been suppressed by illegal killing and nest disturbance associated with grouse moor management. Investigation and enforcement of wildlife crime is the responsibility of the police, and Natural England works closely with the police and the National Wildlife Crime Unit to support their investigations. However, law enforcement alone has, to date, failed to stop the illegal killing of hen harriers, and ways of encouraging coexistence of hen harriers and grouse shooting interests have been explored, in partnership with game shooting organisations.
One way of promoting coexistence, brood management, involves maintaining the density of hen harrier nests on grouse moors at a set level, by removing the eggs and/or chicks from hen harrier nests under licence, rearing the birds in captivity, and releasing them back into the wild at a suitable location once able to fly and disperse. This was predicted to increase the confidence of moorland managers that the predation and disturbance of grouse by nesting hen harriers could be legally managed at levels compatible with grouse shooting, and in turn lead to changes in attitudes and reduced illegal killing of hen harriers.
A plan to experimentally trial brood management was set out in the 2016 Hen Harrier Action Plan. Research licences to carry out brood management of hen harriers were issued from 2018 to 2024, with brood management carried out during 2019 to 2023 by a partnership of the Moorland Association, the International Centre for Birds of Prey, the Game and Wildlife Conservation Trust, the Hawk and Owl Trust and Natural England. Over that period, 15 broods were taken from the wild, with the young birds later released, many carrying satellite tags. Records were kept of numbers and habitat of nesting hen harriers in England, survival rates of tagged birds (both wild and brood managed), and incidents of illegal killing. Two social science studies and a population modelling analysis were carried out.
Key results from the trial were:
- A substantial increase in nesting hen harriers in England was seen during the trial. In the initial years of the trial, the numbers of hen harriers nesting in areas managed for grouse shooting increased significantly. This increase was mainly seen in grouse shooting areas where brood management was available.
- Illegal killing of hen harriers has continued throughout the trial. However, crime 'hotspot’ areas are not the same areas where brood management has been used. It is unclear whether this was because of the effects of brood management, or because those less likely to be involved in illegal killing were more likely to take part in the trial.
- The technique of captive rearing and releasing hen harriers was found to be technically possible with no negative effects on birds.
- While the act of rearing some chicks safely in captivity (sometimes called ‘headstarting’) is likely to have caused a slight increase in the numbers of birds that successfully fledged, the numbers reared in this way were too small to explain the substantial increase in wild nesting pairs seen. Instead, the increase is thought to be due to wild birds being either more likely to survive or more likely to settle and breed, according to commissioned research carried out by the British Trust for Ornithology.
- Satellite-tagged birds have not shown first-year survival rates at levels that would be expected from populations with no illegal killing. However, this does not rule out some improvement in survival rates, potentially of specific age classes.
- One social science study of moorland managers indicated that the availability of brood management allays concerns about hen harriers increasing so much that they ‘overrun’ grouse moors, i.e. increasing to the extent that the grouse moor becomes unprofitable.
- In a wider survey, carried out by the National Centre for Social Research in 2024, moorland managers generally agreed that brood management had contributed to the observed increase in numbers of hen harriers. Two broad and differing explanations were given for this increase. Many expressed beliefs that hen harrier numbers had increased due to direct benefits of captive rearing. However, as outlined above, this was not supported by commissioned research (population modelling). The other explanation was that brood management had led to increased acceptance of hen harriers and confidence that their impacts on grouse could be effectively managed.
- This survey also revealed that around half of moorland managers thought that the trial had led to increased predation and disturbance of grouse by hen harriers on participating estates. Many said that a wider roll-out of brood management would be impractical.
- Moorland managers reported that the benefits of brood management included that it provided an opportunity to demonstrate their support for grouse shooting as a sport and their commitment to wildlife conservation.
A Natural England-led evaluation of the evidence has concluded that it is likely that the availability of brood management has led to more hen harriers successfully breeding on grouse moors. The social science research suggests that this is unlikely to be due solely to an increase in moorland managers’ confidence that the impacts of hen harriers on grouse can be effectively managed. Instead, motivations to increase hen harrier numbers could be attributed to moorland managers’ desire to demonstrate a commitment to wildlife conservation and to grouse shooting as a sport more widely, despite a cost to business, with brood management working as a ‘safety net’ to allay concerns about hen harrier numbers increasing to levels at which grouse shooting would be uneconomical.
While it appears likely that illegal killing and disturbance of nesting hen harriers has reduced in some areas, resulting in increased nesting success on some grouse moors, these increases have been seen alongside unacceptable ongoing illegal killing. It is likely that these observations reflect substantial variation in attitudes and behaviours across different shooting estates.
It follows that a range of approaches may be required to reduce illegal killing on grouse moors and increase hen harrier numbers in future, potentially ranging from co-operative approaches to mitigate the impacts of hen harriers on grouse and support responsible grouse moor management, to monitoring and enforcement activities designed to tackle illegal killing and disturbance, depending on location and situation.
The commissioned reports and evaluation were reviewed by the trial’s Scientific Advisory Group and Natural England’s Science Advisory Committee. These groups agreed that brood management, during the trial, is likely to have contributed to an increase in the hen harrier population, but noted uncertainty over the underlying mechanism, and commented on the role of the active surveillance of hen harriers that happened at the same time.
The results and conclusions summarised above are detailed in four research reports, covering population modelling, social science, and evaluation. These are in the process of publication, and this blog will be updated with links to the full documents when they are published.
This evidence will be available to inform decisions on whether to issue any future licences for brood management of hen harriers. At time of publication, no decisions have been made on any future licences.
Acknowledgements
The Brood Management Trial was a partnership project between the Moorland Association, the International Centre for Birds of Prey, Natural England, the Game and Wildlife Conservation Trust and the Hawk and Owl Trust. With the conclusion of the trial, this partnership has now closed. We thank the members of the trial’s Scientific Advisory Group and we are grateful to the partners, organisations, landowners and land managers who have worked closely with us throughout the trial, supported our social and ornithological research, welcomed our fieldwork and monitoring staff, and demonstrated commitment to the goal of hen harrier conservation and human-wildlife coexistence.
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