Hen Harriers: 1,150% Increase Is a Conservation Success Story

There was a significant increase of 1,150% in hen harrier numbers in England between 2016 and 2023. This figure is derived from Natural England data and was included in an RSPB report. This remarkable growth is a testament to the success of collaborative conservation efforts.

Context of Population Recovery and Status

• From Near Extinction to Record Highs: As recently as 2013, there were no successful hen harrier nests in England. In stark contrast, the hen harrier population in England has now reached its highest level in 100 or even 200 years. In 2023, a record 141 chicks fledged successfully. This represents a "complete turnaround" for the species.

• Geographic Expansion: Successful nests have been reported across various northern English counties including County Durham, Cumbria, Lancashire, Northumberland, and Yorkshire. There are also reports of birds exploring new territories, such as the Lake District, and being tracked as far south as Somerset.

• Favourable Condition: The population increase has led to the Special Protection Areas (Forest of Bowland and North Pennines) reaching "favourable condition". Areas specifically designated for hen harriers are believed to now have sufficient numbers to be classified as being in a 'favourable condition'.

Key Factors Attributed to the Recovery

The recovery can be largely attributed to the Defra-led Hen Harrier Joint Action Plan, established in 2016, and particularly the Hen Harrier Brood Management Trial, which began in 2018.

Brood Management Trial

This trial quadrupled the harrier population in five years. It involves taking eggs or chicks from nests in areas with high harrier densities, rearing them in captivity at a specialist bird of prey centre, and then releasing them back into suitable habitat in their general area.

The trial has seen 58 chicks successfully take to the wing in total. Monitoring has shown that birds reared in the trial have gone on to successfully breed in the wild, indicating no adverse effects on their behavior or breeding ability. Furthermore, the survival rate for brood-managed birds from fledging through the difficult winter months to the following May is reported to be 44%, nearly double the 24% for wild birds.

Role of Grouse Moors and Gamekeepers

The crucial role of land managed for grouse shooting is clear to see in this recovery.

• Habitat and Nests: 80% of successful hen harrier nests are found on driven grouse moors, even though these areas constitute only 50% of the suitable upland habitat. Grouse moors host more hen harrier nests than all RSPB nature reserves combined.

• Management Practices: Grouse moors provide an ideal environment for hen harriers by controlling predator numbers (such as foxes, stoats, weasels, crows, and gulls), especially during the egg-laying season, which boosts fledging success. They also offer extensive suitable territory with diverse vegetation, minimal human disturbance, and abundant food sources like small mammals and other bird chicks. Gamekeepers have also provided supplementary feeding to some birds, which is linked to increased nesting attempts.

• The process of taking birds into captivity and releasing them had no negative effects on the birds themselves. Natural England's evaluation concluded that the brood management trial led to more hen harriers successfully breeding on grouse moors, primarily because the scheme gave moorland managers confidence in managing the impact of harriers on grouse.

Nuance from Population Modelling - BTO Report

A report commissioned by Natural England from the British Trust for Ornithology (BTO) used population modelling to investigate the rapid increase in hen harriers. The models suggest that in addition to brood management, the increase was due to improvements in either survival rates or settlement rates, or a combination of both.

• Settlement Rates: "Settlement" refers to the rate at which breeding-age birds initiate recorded breeding attempts and the survival of these attempts to detection. The models found that a reduction in disturbance during the pre-breeding period, potentially due to the presence of brood management inadvertently reducing the incentive for such disturbance, could lead to more birds attempting to breed and more early attempts surviving.

• The BTO report notes that the lack of similar increases in neighboring populations like Wales and southern Scotland suggests that large-scale environmental factors are unlikely to be the primary driver in England.

Licensing and Future Challenges

Although the brood management trial was successful, Natural England recently chose not to approve the Moorland Association's application for a long-term conservation licence, primarily due to Natural England's belief that satellite tagging is required for conservation goals, which the Moorland Association disputes due to cost, complexity, and trust issues. The trial's success itself led to a reduction in available release sites due to complex licence conditions.

Environmental Factors

Despite the overall positive trend, the population remains vulnerable. The significant drop in breeding attempts in 2024 (from 54 in 2023 to 34) is attributed to exceptionally wet weather, which impacted female health, prey availability (e.g., voles), and overall nesting behavior. Other factors like disturbance from walkers and increased predation by other raptors may also affect ground-nesting hen harriers.

Conclusion

In summary, the 1,150% increase in hen harrier numbers from 2016-2023 reflects a dramatic and widely celebrated recovery in England, largely credited to the Defra-led Brood Management Trial and the managed grouse moor environment.

While the BTO report provides a more nuanced understanding of the population dynamics, emphasizing improved survival and settlement rates, there remains a strong divergence in opinion with organizations like the RSPB regarding the role of persecution and the interpretation of data. The future sustainability of this recovery hinges on ongoing collaboration and the resolution of licensing challenges.

📧 Keep updated on this and all moorland issues - sign up for our FREE weekly newsletter.