How Predator Control Trebles Moorland Bird Breeding Success
- Rob Beeson
- Apr 29
- 9 min read
Updated: May 2
The uplands are home to incredible wildlife, including ground-nesting birds like curlew, lapwing and red grouse. Sadly, many of these species have faced worrying population declines in recent decades. Conservation efforts often focus on improving habitats, like managing heather through burning and managing grazing. But what about the impact of predators?
Native predators can significantly affect the population size of their prey. For ground-nesting birds, predators like foxes and crows are a major threat to eggs and chicks. These generalist predators have actually increased in recent years, partly due to more food availability and fewer gamekeepers on the land.
This blog post examines an 8-year field experiment conducted on moorland in northern England that looked specifically at how manipulating the abundance of legally controllable predators impacted the breeding success and numbers of seven ground-nesting bird species.
Jump to Section
Unpacking the Study: Design and Species
To understand the impact of predator control, researchers set up a large-scale experiment across four study plots (ranging from 9.3 to 14.4 km²) in Northumberland.
These plots were chosen because they were similar in habitat composition, featuring mosaics of heather-dominated heath, heath/acid grassland, and areas with grasses and rushes, and were grazed by sheep. Crucially, there was negligible predator control on these plots or surrounding areas before the experiment began.
The experiment ran for eight years, from 2000 to 2008. It used a paired plot design. Two plots formed one pair, where predator control was applied to one, then switched to the other partway through.
Another pair of plots had predator control randomized and kept the same treatment throughout. This design allowed researchers to compare what happened with and without predator management over time.
A key goal was to isolate the effect of predator control. To achieve this, habitat management practices like sheep grazing and heather burning were kept at consistent levels across all plots throughout the experiment.
Researchers monitored vegetation composition and structure annually to confirm there were no significant differences between the predator-controlled and non-controlled areas. This consistency means any observed differences in bird populations are much more likely to be due to the predator control itself, not changes in habitat.
Who Was Studied? Our Vulnerable Ground-Nesters
The study focused on several species of ground-nesting birds that are particularly vulnerable to predation and are of conservation concern in the UK.
The species monitored for both breeding success and abundance were:
Lapwing (Vanellus vanellus)
Golden Plover (Pluvialis apricaria)
Curlew (Numenius arquata)
Red Grouse (Lagopus lagopus scoticus)
Meadow Pipit (Anthus pratensis)
Additionally, Snipe (Gallinago gallinago) and Skylark (Alauda arvensis) abundance was monitored.
These birds were selected because they represent different types of ground-nesters and are sufficiently numerous on this kind of moorland to allow for meaningful data collection.
Which Predators Were Managed?
The predator control efforts targeted legally controllable species known to prey on ground-nesting birds and their nests. This was carried out year-round by full-time gamekeepers using legal techniques.
The main target predators were:
Fox (Vulpes vulpes)
Carrion Crow (Corvus corone)
Stoat (Mustela ermina)
Weasel (Mustela nivalis)
It's important to note that legally protected predators, such as raptors (like buzzards, kestrels, merlins, peregrines, short-eared owls, goshawks, hen harriers), badgers, and otters, were not killed or disturbed.
Predator abundance was monitored regularly using different methods: fox numbers via scat collection along routes, stoats and weasels via tracking tunnels, and carrion crows and raptors via timed transect counts.
What Happened to the Predators?
The predator control efforts were effective in reducing the numbers of the key target species.
Fox Abundance Reduced: In plot-years with predator control, fox abundance was 43% lower than in plots without control.
Carrion Crow Abundance Plummeted: Carrion crow abundance was significantly reduced, being 78% lower with predator control.
Stoats and Weasels: Stoat abundance was already low across all plots. While spring weasel abundance didn't change with treatment, autumn weasel abundance was actually higher on predator-controlled plots. The study acknowledges that immigration from surrounding areas likely meant predator numbers didn't decrease consistently over the years of control within the plots.
Interestingly, the study also found that more raptors were recorded on plots under the predator control treatment. This included species like buzzards, kestrels, and merlins. The study didn't try to assess the impact of these protected raptors on bird success.
The Big Payoff: Bird Breeding Success Soars
This is where the results get exciting for bird conservation. The study found a dramatic improvement in the breeding success of most monitored species when predators were controlled.
Breeding success was measured differently depending on the species. For waders (lapwing, golden plover, curlew), researchers used behavioural observations of adults to determine if they had chicks, as visiting nests can disturb them and potentially attract predators.
For meadow pipits, nest monitoring was used. For red grouse, breeding success was measured as the ratio of young birds to adults later in the season. Too few skylark nests were found for analysis.
The results showed a significant increase in the proportion of pairs successfully fledging young for five of the seven species:
Average Increase: Predator control led to an average threefold increase in the breeding success of lapwing, golden plover, curlew, red grouse, and meadow pipit.
Lapwing: Breeding success was 3.5 times greater with predator control (57% of pairs fledged young) compared to no control (19%).
Golden Plover: Breeding success was 4.2 times greater with predator control (75% of pairs fledged young) compared to no control (18%).
Curlew: Breeding success was 3.4 times greater with predator control (51% of pairs fledged young) compared to no control (15%).
Red Grouse: Breeding success (young to adult ratio) was 3.2 times greater with predator control (1.93) compared to no control (0.60).
Meadow Pipit: Breeding success (percentage of pairs fledging young) was twice as high with predator control (52%) compared to no control (28%).
These findings strongly suggest that reducing predator numbers, particularly foxes and crows, makes it much more likely for these ground-nesting birds to successfully raise their young on moorland.
The study highlights how crucial this improvement is, particularly for species like lapwing and curlew. Based on estimates, a lapwing pair needs to produce about 0.87–0.97 fledglings per year to maintain a stable population, and curlews need 0.48–0.62 fledglings per pair.
With only 19% and 15% success rates without predator control, successful pairs would have to fledge an unrealistic number of chicks (4.6 for lapwing, 3.2 for curlew, given typical clutch sizes of 4 eggs) just to keep the numbers stable. This low success rate without control would inevitably lead to population declines.
Beyond Success: Changes in Bird Numbers
Improving breeding success is a vital step, but does it translate into more birds on the ground in the following years? The study also looked at changes in breeding numbers.
The results showed that predator control did lead to increases in the breeding populations for some species:
Lapwing, Curlew, Golden Plover, and Red Grouse: These species showed significant increases in breeding numbers where predator control was implemented (at least 14% increase per year). In contrast, their numbers declined (at least 17% per year) in areas without predator control.
Connecting Success to Numbers: The study found that higher breeding success in the previous year significantly explained some of the year-to-year increases in numbers for lapwing, golden plover, and red grouse. This suggests that having more young successfully fledge likely contributes to a larger breeding population the following year (or after a few years for curlew, which breed later).
The study used time lags based on when each species typically recruits new breeders into the population (e.g., one year for lapwing, golden plover, red grouse, meadow pipit, skylark, snipe, and three years for curlew).
They found the positive effect on abundance was generally linked to predator control or breeding success in previous years, rather than just in the current year. This means birds weren't necessarily choosing to nest in areas with low predator numbers this year, but rather the population was growing because more young birds were produced in previous years due to predator control.
Species Not Showing Abundance Increases: Sniper, meadow pipit, and skylark breeding numbers did not show a significant positive effect of predator control in either the current or previous year. This could be due to various factors, potentially including lower rates of birds returning to breed in the same area (philopatry) compared to species like red grouse.
Why Does This Matter for Conservation?
The findings of this study have significant implications for how we manage moorland habitats and conserve vulnerable bird species.
Predator Control as a Conservation Tool
This research demonstrates that controlling predators like foxes and crows is a potentially important management tool for conserving a range of threatened species, particularly ground-nesting birds. It shows a clear benefit, leading to both higher breeding success and increased populations for several key species.
Complementing Habitat Management
Conservation efforts often focus heavily on habitat improvement. While essential, this study suggests that habitat work alone may not be enough to reverse declines if predation pressure is high. The consistent habitat conditions across the study plots underline that the observed benefits came from predator control, not just better habitat. The study argues that public funds used for habitat improvement could be more effective if predator management is also implemented alongside it.
The Role of Grouse Moor Management
The study notes that on upland moorland in the UK, the benefits of predator control for conservation are often a by-product of management undertaken primarily to maximize red grouse numbers for shooting. Legal predator control is a well-established technique on grouse moors.
A previous study found that species like golden plover, curlew, lapwing, and redshank were more abundant on moorland managed for red grouse shooting compared to areas without this management, while meadow pipit and skylark were less abundant. This experiment provides strong evidence that predator control, a key part of grouse moor management, is a plausible explanation for the higher densities of some of these species.
Predicting Population Declines Without Control
The authors highlight the potential consequences if predator control were to stop on areas currently managed this way. Given that a large proportion (74%) of upland Special Protection Areas (SPAs) designated for breeding birds in England are managed as grouse moor, the cessation of predator control could lead to considerable population declines in a range of bird species within these important conservation areas.
Looking Ahead: Incorporating Predator Control into Conservation Efforts
The researchers suggest that predator control should be considered as a more general tool for conserving various bird species across different habitats. They specifically recommend that it should be incorporated into agri-environment schemes, particularly when the goal is to help threatened wader populations.
In many countries, agri-environment schemes provide funds for landowners to manage land for conservation. While these schemes often support habitat management, they may not adequately address the negative impacts of predation. Adding predator control prescriptions to these schemes could provide a more comprehensive approach.
When conservation goals can be met alongside privately funded land uses, such as gamebird hunting which often incorporates predator control, the study argues that these approaches should be strongly encouraged.
Conclusion
This rigorous 8-year field experiment provides compelling evidence that legal predator control significantly boosts the breeding success of several ground-nesting moorland bird species, including lapwing, golden plover, curlew, red grouse, and meadow pipit. More importantly, it demonstrates that this improved success translates into increased breeding numbers for species like lapwing, golden plover, curlew, and red grouse, helping to reverse population declines observed in the absence of control.
By maintaining consistent habitat conditions, the study clearly showed that the benefits were directly attributable to the reduction in predator numbers, primarily foxes and carrion crows.
The findings underscore that predator management is a powerful tool that can complement traditional habitat-focused conservation strategies. Incorporating legal predator control into broader conservation plans, such as agri-environment schemes, holds significant potential for supporting the recovery and maintenance of vulnerable ground-nesting bird populations on moorland.
Think about it: How can we ensure that conservation efforts take a comprehensive approach, addressing all limiting factors like predation, alongside essential habitat work? This research suggests that for some species, managing predators isn't just beneficial - it might be essential to securing their future on our landscapes.
UPDATE: 10 Years on from the Experiment - Bird Populations Fall Dramatically
The researchers returned to Northumberland ten years after the experiment ended to find out what had happened to the predator and ground-nesting bird populations. The figures below confirm that predator control is essential for protecting our moorland birds:
Fox: 78% increase
Carrion Crow: 127% increase
Black Grouse: local extinction
Grey Partridge: local extinction
Red Grouse: 71% decline
Golden Plover: 81% decline
Snipe: 76% decline
Curlew: 24% decline
Lapwing: 58% decline
📧 Stay updated on all moorland issues - sign up for our free Newsletter.
