2020

Ludwig, S.C., Roos, S., Baines, D., 2020. Fluctuations in field vole abundance indirectly influence red grouse productivity via a shared predator guild. Wildlife Biology 2020: wlb.00642.

https://doi.org/10.2981/wlb.00642

Abstract

Changes in the abundance of one prey species may indirectly affect other prey species by triggering responses in generalist predators. Here we examine relationships between two prey species that do not compete directly, the field vole Microtus agrestis, a common rodent with fluctuating populations, and the red grouse Lagopus lagopus scotica, a gamebird inhabiting open moorland, during a 27-year study on a moor in south-west Scotland. First, we test whether vole abundance was related to grouse density and demographic rates. Second, we test whether vole abundance was related to abundance indices of four common predators of both voles and grouse (red fox Vulpes vulpes, weasel Mustela nivalis, hen harrier Circus cyaneus and common buzzard Buteo buteo). Third, we test whether these vole-grouse and vole-predator relationships differ in relation to grouse management, which includes the culling of foxes and weasels. We found no association between vole abundance and grouse densities, adult summer survival or nesting success. However, the ratio of young grouse per adult and the proportion of female grouse with broods in July were negatively associated with field vole abundance, suggesting increased predation of grouse chicks in years with high vole abundance. Fox indices showed a weak positive association with vole abundance when their numbers were not controlled, whilst weasel indices showed no relationship with voles. The numbers of breeding hen harriers and buzzards were also not associated with vole abundance, but the number of buzzard sightings was higher when voles were more plentiful. Our results are consistent with a negative interaction between field voles and red grouse chick survival in a pattern expected for apparent competition. Although the underlying mechanisms could not be disentangled, this interaction may be at least partly mediated by rodent-hunting raptors such as buzzards and, in periods without grouse management, foxes.

Ludwig SC, Aebischer NJ, Richardson M, Roos S, Thompson DBA, Wilson JD & Baines D (2020) Differential responses of heather and red grouse to long-term spatio-temporal variation in sheep grazing. Biodiversity and Conservation 29: 2689-2710.

https://rdcu.be/b4FZl

Abstract

During the last century, afforestation and intensification of sheep grazing in the British uplands have led to widespread declines in globally rare heather moorland. We quantified changes in heather cover over 70 years in relation to changes in sheep grazing on Langholm Moor, and examined the impact on red grouse, a gamebird inhabiting heather moorland. Between 1948 and 2009, when grazed heavily by sheep, heather-dominated vegetation declined from 53% to 14% cover. Large-scale sheep reductions from 2011 then allowed increase of heather-dominated vegetation cover to 18% by 2015. However, changes in heather cover were associated with changes in grouse abundance only where heather-dominated cover was reduced below thresholds of 27% (95% CL 18-36%; pre-breeding) and 17% (95% CL 13-20%; post-breeding). The number of grouse shot between 1951 and 1992 remained high where 37-65% of dominant heather cover was retained, but then declined between 1992 and 1996 following increased predation by raptors, leading to the cessation of shooting. Subsequently, grouse densities fluctuated in relation to periodic management by gamekeepers (1992-1999 and 2008-2016), but heather loss continued possibly until 2011, and predation in this context prevented sustained increases sufficient for 'driven' shooting. Grouse shooting provides an economic incentive to maintain and restore heather moorland. On Langholm Moor, however, afforestation in the surrounding landscape and isolation from other heather moors may have led to a grouse population less well buffered against growing predation pressure, especially outside keepered periods. As grouse shooting could not be restored, the future management of the moor remains uncertain.

Ludwig SC, Roos S, Rollie CJ, Baines D (2020) Long-term changes in the abundance and breeding success of raptors and ravens in periods of varying management of a Scottish grouse moor. Avian Conservation and Ecology 15(1): 21.

http://www.ace-eco.org/vol15/iss1/art21/

Abstract

Management of heather moorland for driven Red Grouse Lagopus lagopus scotica shooting in the British uplands may benefit some raptors by reducing predation risk, especially when breeding, and by increasing food availability. We describe changes in abundance and breeding success of four raptor species and Raven Corvus corax during a 27-year study on a grouse moor in SW Scotland in relation to whether or not the moor was managed by gamekeepers. Ground-nesting raptors, Hen Harrier Circus cyaneus and Merlin Falco columbarius, increased during periods of grouse moor management and had a higher proportion of successful nesting attempts. Predation was the main apparent cause of breeding failure. In contrast, grouse moor management did not influence either abundance or breeding success of tree- and crag-nesting species, i.e. Peregrine Falco peregrinus, Common Buzzard Buteo buteo and Raven. Buzzard sightings increased during the study, in line with their national recovery, whereas Peregrine and Raven showed little change in abundance. The results of our study highlight that management for Red Grouse can benefit both Hen Harrier and Merlin, but on a UK scale these benefits to Hen Harriers, but not Merlin, are outweighed by their illegal killing, caused by fears that their consumption of Red Grouse can undermine the economics of grouse moor management.

2019

Francksen RM, Aebischer NJ, Ludwig SC, Baines D, Whittingham MJ (2019) Measures of predator diet alone may underestimate the collective impact on prey: Common buzzard Buteo buteo consumption of economically important red grouse Lagopus lagopus scotica. PLOS ONE 14(8): e0221404.

https://doi.org/10.1371/journal.pone.0221404

Abstract

Human-wildlife conflicts often centre on economic loss caused by wildlife. Yet despite being a major issue for land managers, estimating total prey losses to predation can be difficult. Estimating impacts of protected wildlife on economically important prey can also help management decisions to be evidence-led. The recovery in population and range of common buzzards Buteo buteo in Britain has brought them into conflict with some gamebird interests. However, the magnitude of any impact is poorly understood. We used bioenergetics models that combine measures of buzzard abundance from field surveys with diets assessed by using cameras at nests, prey remains and pellet analysis, to estimate their impact on red grouse Lagopus lagopus scotica on a large (115 km²) moor managed for red grouse shooting in Scotland. Whilst grouse consumption by individual buzzards was lower than previous estimates for other raptor species present on our study site, total consumption could be greater given an estimated 55–73 buzzards were present on the study site year-round. Averaging across diet assessment methods, consumption models estimated that during each of three breeding seasons (April-July 2011–2013), the buzzards foraging on our study site consumed 73–141 adult grouse and 77–185 chicks (depending on year). This represented 5–11% of adult grouse present in April (22–67% of estimated adult mortality) and 2–5% of chicks that hatched (3–9% of estimated chick mortality). During two non-breeding seasons (August-March), consumption models using pellet analysis estimated that buzzards ate a total of 242–400 grouse, equivalent to 7–11% of those present at the start of August and 14–33% of estimated grouse mortality during the non-breeding season. Buzzard consumption of grouse has the potential to lead to non-trivial economic loss to grouse managers, but only if buzzards predated the grouse they ate, and if grouse mortality is additive to other causes.

Ludwig SC, Roos S, Baines D (2019) Responses of breeding waders to restoration of grouse management on a moor in South-West Scotland. Journal of Ornithology 160: 789–797.

https://link.springer.com/article/10.1007%2Fs10336-019-01667-6

Abstract

Worldwide, many wader species have recently exhibited steep declines in range and abundance. Low productivity, frequently associated with predation, is considered a major proximate driver of declines and often reflects underlying land use and habitat change. We hypothesised that restoration of grouse moor management, which includes control of predators and heather habitat management, would halt and reverse these declines. We monitored changes in the abundance of four upland-breeding wader species following restoration of grouse moor management at Langholm Moor in South-west Scotland from 2008 to 2017. Here, Curlew, Golden Plover and Lapwing had previously declined when management ceased, whereas Snipe had increased. During the 10-year study period, Curlew numbers increased on average by 10% per annum, Golden Plover numbers by 16% and Snipe numbers by 21%, whereas Lapwing numbers did not change. These local trends contrast with national and regional trends over the same period, which all showed declines of all these species. However, the population trends for Curlew and Snipe did not differ in relation to habitat management for Red Grouse, suggesting that population increases were primarily associated with predator control across the whole study area. Our results support the hypothesis that restoring predator control as part of grouse moor management can reverse declines of some wader species. At Langholm, full recovery to levels observed prior to management cessation may have been constrained by delayed recruitment within a time-restricted study period in combination with low initial numbers, availability and isolation of suitable habitat, and incomplete predator removal.

2018

Sonja C. Ludwig, Nicholas J. Aebischer, Damian Bubb, Michael Richardson, Staffan Roos, Jeremy D. Wilson and David Baines. 2018. Population responses of Red Grouse Lagopus lagopus scotica to expansion of heather Calluna vulgaris cover on a Scottish grouse moor. Avian Conservation and Ecology 13 (2):14.

http://www.ace-eco.org/vol13/iss2/art14/

Abstract

Loss of heather Calluna vulgaris-dominated moorland in Britain has been associated with long-term declines in Red Grouse Lagopus lagopus scotica, a gamebird of economic importance. We tested whether restoring heather habitat on a grouse moor in southwest Scotland, where heather was previously in decline, improved Red Grouse density, productivity, and survival. We analyzed spatial and temporal relationships between Red Grouse demographic rates, estimated from counts, and habitat variables measured from ground and aerial vegetation surveys. Reductions in sheep Ovis aries grazing and other heather restoration measures (i.e. burning and cutting, and in some areas reseeding of heather following herbicide treatment to reduce grass dominance) increased total heather cover by 10% and the area of heather-dominated vegetation by 30% within six years. Prebreeding, and for aerial surveys also postbreeding, densities of Red Grouse were highest in areas with more heather cover (range: 0–92%), and prebreeding densities increased more where heather recovery was greatest. However, we found no relationship between heather cover and Red Grouse productivity or survival rates, the latter also when rates were estimated from radio-tagged individuals. Changes in heather cover were not associated with changes in postbreeding densities or survival of Red Grouse, although they were positively related to change in productivity for aerial surveys. Overall, management for Red Grouse had a larger effect on density and productivity than reductions in sheep grazing. This is the first study examining Red Grouse responses in relation to changes in heather cover within the same site, in contrast to previous between-moor comparisons, where other factors may have contributed to variation in Red Grouse demography. Our results suggest that, in the long term, heather restoration has the potential to increase Red Grouse carrying capacity, but realizing this potential first requires improving Red Grouse demographic rates.

Sonja C. Ludwig, Nicholas J. Aebischer, Damian Bubb, Staffan Roos and David Baines (2018) Survival of chicks and adults explains variation in population growth in a recovering red grouse Lagopus lagopus scotica population. Wildlife Biology 2018: wlb.00430.

https://doi.org/10.2981/wlb.00430

Abstract

Understanding demographic mechanisms is key to managing animal populations, both in conservation and game management. We examine which life-stages contributed most to population growth in a recovering red grouse Lagopus lagopus scotica population following restoration of management aimed at resuming economically viable harvesting. Demographic parameters derived from biannual grouse counts and from radio-tagged individuals were analysed using ‘standard demographic accounting’. When parameter estimates were based on counts, a combination of adult summer and winter survival appeared to contribute most to population change. When based on radio-tagged birds, deemed more reliable because of independence between parameters and years, adult summer survival and chick survival contributed most to population change. The contributions of clutch size, nesting success (i.e. the proportion of nests with =1 egg hatching) and hatching success (proportion of eggs hatching in successful nests) were negligible. Overall, the survival rate of adults and chicks contributed most to annual population change and reduced the rate of population recovery. Analysis of grouse carcasses found that 82% were associated with signs of predation or scavenging by raptors. Rates of juvenile production exceeded those of adult mortality, allowing modest population growth, but insufficient to resume economically viable harvesting.

Sonja C. Ludwig, Aly McCluskie, Paula Keane, Catherine Barlow, Richard M. Francksen, Damian Bubb, Staffan Roos, Nicholas J. Aebischer & David Baines (2018) Diversionary feeding and nestling diet of Hen Harriers Circus cyaneus. Bird Study 65 (4): 431-443.

https://doi.org/10.1080/00063657.2018.1519524

Abstract

Capsule: Diversionary feeding reduced Hen Harrier Circus cyaneus nestlings’ natural food intake by half. Red Grouse Lagopus lagopus scotica chicks constituted 0–4% of all nestling food items. Annually, this reduced annual grouse chick production by 0-6%.

Aim: To quantify proportions of diversionary and natural food (including grouse) delivered to Hen Harrier nestlings in relation to brood size, male status and natural prey abundance.

Methods: We recorded diversionary food provisioned to 25 Hen Harrier broods (2008–15) and studied the diet of 15 broods using observations from hides, nest cameras and regurgitated pellet analysis. Variation in nestling diet was analysed using compositional analysis.

Results: Hen Harriers took 76% of diversionary food provided. Depending on assessment method, average nestling diet was 44-53% diversionary food, 39-55% natural prey (including 24-45% passerines, 4-15% small mammals, 0-4% grouse chicks) and 0-9% unknown items. The amount of diversionary food consumed was not influenced by male status, brood size or natural prey abundance. The number of Red Grouse chicks delivered annually was 34-100% lower than expected under unfed conditions, however, the confidence intervals associated with these estimates were large.

Conclusion: Diversionary food influenced Hen Harrier nestling diet and reduced the number of Red Grouse chicks taken relative to modelled predictions. It may help reduce conflict between Hen Harrier conservation and Red Grouse shooting, but only if overall grouse productivity is thereby maintained or increased.

2017

Ludwig, S. C., Roos, S., Bubb, D. & Baines, D. (2017) Long-term trends in abundance and breeding success of red grouse and hen harriers in relation to changing management of a Scottish grouse moor. Wildlife Biology 2017: wlb.00246.

http://www.bioone.org/doi/pdf/10.2981/wlb.00246

Abstract

Large areas of heather moorland in the British uplands are managed for shooting red grouse Lagopus lagopus scotica. However, there has been a long-standing conflict between grouse moor management and the conservation of raptors, particularly the hen harrier Circus cyaneus. Langholm Moor, a grouse moor in south-west Scotland, has hosted studies aiming to resolve this conflict for 24 years. Between 1992 and 1997, whilst managed as a grouse moor, hen harrier numbers increased from two to 20 breeding females, and raptor predation removed large proportions of both adult grouse and chicks. As driven shooting was no longer viable, grouse moor management ceased in 1999, and was not restored until 2008. This paper considers how cessation and subsequent restoration of grouse moor management, which involved heather management and legal control of generalist predators, affected the abundance and breeding success of red grouse and hen harrier, as well as the abundance of their perceived key predators; red fox Vulpes vulpes and carrion crow Corvus corone. Grouse moor management had a positive effect on abundance and breeding success of grouse and harriers, which were two- to three-fold higher when fox indices and crow abundance were reduced by 50-70%. Fox indices were negatively correlated with red grouse density and harrier breeding success, whereas crows were negatively correlated with grouse breeding success.

This study confirms that both grouse and harriers can benefit from grouse moor management, if harriers are not persecuted. However, restoration of grouse moor management, in combination with diversionary feeding of harriers, has not yet resulted in a sufficiently increased grouse density to allow driven shooting on Langholm Moor, and thus the management to be considered as economically viable.

Francksen, R.F., Whittingham, M.J., Ludwig, S.C., Roos, S., Baines, D. (2017) Numerical and functional responses of common buzzard Buteo buteo on a Scottish grouse moor. Ibis 159: 541-553.

http://onlinelibrary.wiley.com/doi/10.1111/ibi.12471/full

Abstract

Predators will often respond to reductions in preferred prey by switching to alternative prey resources. However, this may not apply to all alternative prey groups in patchy landscapes. We investigated the demographic and aggregative numerical and functional responses of Common Buzzards Buteo buteo in relation to variations in prey abundance on a moor managed for Red Grouse Lagopus lagopus scotica in south-west Scotland over three consecutive breeding and non-breeding seasons. We predicted that predation of Red Grouse by Buzzards would increase when abundance of their preferred Field Vole Microtus agrestis prey declined. As vole abundance fluctuated, Buzzards responded functionally by eating voles in relation to their abundance, but they did not respond demographically in terms of either breeding success or density. During a vole crash year, Buzzards selected a wider range of prey typical of enclosed farmland habitats found on the moorland edge but fewer Grouse from the heather moorland. During a vole peak year, prey remains suggested a linear relationship between Grouse density and the number of Grouse eaten (a Type 1 functional response), which was not evident in either intermediate or vole crash years. Buzzard foraging intensity varied between years as vole abundance fluctuated, and foraging intensity declined with increasing heather cover. Our findings did not support the prediction that predation of Red Grouse would increase when vole abundance was low. Instead, they suggest that Buzzards predated Grouse incidentally while hunting for voles, which may increase when vole abundances are high through promoting foraging in heather moorland habitats where Grouse are more numerous. Our results suggest that declines in their main prey may not result in increased predation of all alternative prey groups when predators inhabit patchy landscapes. We suggest that when investigating predator diet and impacts on prey, knowledge of all resources and habitats that are available to predators is important.

2016

Francksen, R. F., Whittingham, M. J. & Baines, D. (2016) Assessing prey provisioned to common buzzard Buteo buteo chicks: a comparison of methods. Bird Study 63 (3): 303-310.

http://www.tandfonline.com/doi/full/10.1080/00063657.2016.1183111

Abstract
Capsule: Methods of assessing raptor diet carry significant inherent biases which can vary over time.

Aims: To compare methods of assessing Common Buzzard Buteo buteo diet composition and assess how any differences vary between years.

Methods: Diet was assessed at 32 Common Buzzard nests on an area of upland heather moorland in Britain, managed for Red Grouse Lagopus lagopus scotica, over three years. Data obtained from nest cameras were compared with data from prey remains and regurgitated pellets.

Results: Diet composition differed between methods in all years. Methodological differences varied between years in relation to an almost twelve-fold change in Field Vole abundance, a key prey of Common Buzzards, while abundances of alternative prey changed little. Small mammals were underestimated by prey remains in all three years, while herpetofauna were underestimated by prey remains and pellets in two years. Large birds were overestimated by prey remains, significantly so in one year. Pellets overestimated invertebrates in all years. By combining prey remains and pellets, significant yearly variations in biases were eliminated, although the combined measure overestimated large birds and invertebrates.

Conclusion: Our results suggest that future studies should consider not only how chosen methods may affect results, but also how effects can differ between years.

Francksen, R. M., Whittingham, M. J., Ludwig, S. C. & Baines, D. (2016) Winter diet of Common Buzzards Buteo buteo on a Scottish grouse moor. Bird Study 63 (4): 525-532.

http://www.tandfonline.com/doi/full/10.1080/00063657.2016.1238868

Abstract
Capsule: The winter diet of Common Buzzards Buteo buteo on a Red Grouse Lagopus lagopus scotica moor was dominated by small mammals, whilst grouse were a minor prey item.

Aims: To assess winter diet of Common Buzzards from pellets collected at roost sites on and around a managed Red Grouse moor, and to explore temporal, spatial and age-related variation in diet composition.

Methods: Forty-four winter roost sites were located during two winters using a combination of observations from vantage points and individual Common Buzzards equipped with either radio or satellite transmitters. Pellets were collected between October and March each winter and analysed to assess dietary composition.

Results: Small mammals were the main prey in both years, comprising 60–67% of items and occurring in 88–92% of pellets. Diet varied between years, with more lagomorphs and birds (passerines, corvids and pigeons) but fewer Red Grouse eaten when grouse abundance declined. Grouse formed 1.1% and 0.6% of prey items, and occurred in 3% and 2% of pellets from each winter, respectively.

Conclusion: Common Buzzards rely on small mammal prey during winter. When available, Red Grouse are a minor dietary component, the amount of which reflects their abundance in the environment. The opportunism of Common Buzzards can result in temporal variation in winter diet.

Thompson, D.B.A., Roos, S., Bubb, D., Ludwig, S.C. (2016) Hen Harrier. Version 1.0. In: Gaywood, M.J., Boon, P.J., Thompson, D.B.A. & Strachan, I.M. (Eds.) The Species Action Framework Handbook. Scottish Natural Heritage, Battleby, Perth.

http://www.snh.gov.uk/docs/A2169322.pdf

Fingland, K. & Ludwig, S. C. (2015) Clutch abandonment as a result of brood adoption in the red grouse. British Birds 108: 294-295.

https://britishbirds.co.uk/article/british-birds-may-2015/

Seven Year Project Review. The LMDP Directors launched the full review of project progress. The report was produced allowing 2014 data to be included. The project review can be downloaded here.

When the project reached its seventh year, the scientific staff assessed a number of factors and developed statements summarising the progress between 2008 and the end of 2013. These were agreed by the science leads in each of the funding partner organisations, the project's Scientific and Technical Advisory Group, and the project directors. These summary statements can be downloaded here.