The direct and indirect effects of predation by Hen Harriers Circus cyaneus on trends in breeding birds on a Scottish grouse moor

Two phases of an experimental reduction in management at Langholm Moor in southwest Scotland provided an insight into factors that determined trends in the abundance of moorland birds. In 1992 the historical control of breeding Hen Harriers Circus cyaneus stopped and in 2000 grouse moor management was discontinued. Golden Plover Pluvialis apricaria , Lapwing Vanellus vanellus , Curlew Numenius arquata and Red Grouse Lagopus lagopus scoticus declined, whilst Carrion Crow Corvus corone and Snipe Gallinago gallinago increased. Hen Harriers increased from two to 20 breeding females, then declined back to two. Lapwing abundance was positively associated with that of Hen Harriers, and moorland passerines (Skylark Alauda arvensis , Meadow Pipit Anthus pratensis and Stonechat Saxicola torquata ) were negatively associated. Golden Plover, Lapwing, Curlew, Red Grouse, Skylark and Hen Harrier were more abundant when the moor was managed for grouse, whilst Carrion Crow, a common predator of clutches of ground-nesting birds, increased during the second half when management ceased. Increased Crow numbers, together with an increase in Red Foxes Vulpes vulpes , probably contributed to the observed bird declines.     

Changes in upland bird abundances show associations with moorland management

Capsule: Changes in abundance of six bird species showed associations with moorland management.

Aims: To assess responses of breeding birds to moorland management over a 14-year period.

Methods: Vegetation and birds were surveyed at 2–3-year intervals and changes examined in relation to sheep and cattle grazing, vegetation burning and cutting.

Results: Seven correlations between change in management and change in bird abundance were detected, and six between change in vegetation and change in bird abundance. On plots where sheep numbers declined, Golden Plover Pluvialis apricaria and Northern Wheatear Oenanthe oenanthe declined. Where a greater area was burned, Golden Plover increased in the initial post-burning period but Red Grouse Lagopus lagopus scotica declined. Eurasian Curlew Numenius arquata and Sky Lark Alauda arvensis increased where a greater area of moorland vegetation was cut. Whinchat Saxicola rubetra declined with increasing cattle numbers on a plot.

Conclusions: Bird populations respond to changes in moorland management, but these changes are not always associated with detectable changes in vegetation. These responses of moorland breeding birds to management could help refine agri-environment options and other conservation interventions on moorland. Responses differed between bird species, ideally requiring site-specific planning where managing for multiple species is a goal.     

Associations between distance to forest and spatial and temporal variation in abundance of key peatland breeding bird species

Capsule Negative forest edge effects were detected for Willow Ptarmigan (Red Grouse) Lagopus lagopus and Dunlin Calidris alpina.

Aims To investigate the effects of distance to forest on the abundance and changes in abundance of four key peatland breeding bird species, and to measure changes in predatory bird numbers, in the peatlands of northern Scotland.

Methods Bird surveys were carried out in 2000 at 34 plots, covering 197 km² of peatland, and 80 forestry point‐count sites, first surveyed in 1988. Habitat data were also collected in 2000. We used multi‐model inference to investigate the associations between forest distance and other habitat variables, and the abundance, and changes in abundance, of four bird species of economic or conservation importance: Red Grouse, European Golden Plover Pluvialis apricaria, Dunlin and Common Greenshank Tringa nebularia.

Results There was strong evidence that distance to forest was negatively associated with Dunlin abundance and changes in Red Grouse abundance, but only weak evidence for negative associations with Golden Plover abundance and changes in Dunlin abundance. There was no evidence of a forest distance effect on Greenshank. Among predatory birds, there were no significant increases either on peatland plots or in new forestry plantations.

Conclusions This study provides evidence that, for a given habitat quality, Dunlin densities are lower, and Red Grouse declines more likely, near to forest edges, but weak evidence only that Dunlin declines are more likely, and Golden Plover abundance lower, near to forests. These results suggest that for at least two key peatland breeding birds, forest removal is likely to benefit birds breeding on adjacent unafforested peatland.     

Golden Plover Pluvialis apricaria breeding success on a moor managed for shooting Red Grouse Lagopus lagopus

Capsule The best estimate of breeding success was a mean of 0.57 fledglings per pair, which when combined with adult survival rates, successfully explained the observed population trend.

Aims To quantify Golden Plover breeding success on a moor managed for shooting Red Grouse Lagopus lagopus.

Methods An intensive study recorded the fate of individual Golden Plover nests and, using radiotelemetry, chicks. The factors associated with mortality were examined, allowing the construction of a model of breeding success. Adult survival was estimated from return rates of colour-ringed birds.

Results Estimated rates of daily nest survival during laying (0.8636) were significantly lower than during incubation (0.9913). The daily survival rate of chicks less than nine days (0.8868) was significantly lower than for older chicks (0.9792). A population model based on these parameters overestimated the rate of nest losses, but accurately described brood survival and fledging success. Although predation rates were low, poor survival of young chicks through starvation or exposure suggest other factors were limiting breeding success at the study site.

Conclusions Predation rates of Golden Plover nests and chicks can be low on moorlands managed for shooting Red Grouse. However, in the absence of predation, other factors may still reduce chick survival and limit breeding success.     

Correlates of distribution and nesting success in a Welsh upland Eurasian Curlew Numenius arquata population

Capsule: Habitat structure and composition explained spatial variation in breeding distribution and nesting success in a declining upland Eurasian Curlew Numenius arquata population in North Wales.

Aims: To identify environmental correlates of Curlew breeding distribution, nesting success and change in distribution.

Methods: Thirty random 1?km squares stratified by historical population trend were surveyed for Curlew density and nesting success, and habitat- and predation-related variables in a landscape containing agriculturally improved farmland, and moorland that was partly protected and subject to grazing reductions for nature conservation. Analyses tested for associations between Curlew measures and environmental variables.

Results: Curlew breeding density declined by 29% between 1994 and 2008, and was highest in squares comprising a mixture of moorland and agriculturally improved farmland, and in squares with lower vegetation density and higher cover of Nardus stricta (characteristic of rough grazing). Nesting success was positively associated with cover of Trichophorum germanicum (characteristic of mire). Vegetation density was lower than average in squares with the highest Curlew densities, while in the protected area vegetation density was higher than average.

Conclusion: Habitat and vegetation variables influenced Curlew distribution and nesting success in North Wales, largely in line with previous results but with no evidence for predator-related influences. Habitat condition for Curlew in the protected area could probably be increased through targeted increases in grazing alongside the protection of priority habitats.     

Breeding populations of Little Ringed Plover Charadrius dubius and Ringed Plover Charadrius hiaticula in the United Kingdom in 2007

Capsule: The 2007 national survey of the UK breeding population of Little Ringed Plovers shows a further spread into Scotland and Wales since the previous survey in 1984. In contrast, there has been a significant decrease in the Ringed Plover breeding population.

Aims: To provide new breeding population estimates in the UK and Great Britain for Little Ringed Plover Charadrius dubius and Ringed Plover Charadrius hiaticula in 2007 and investigate changes in breeding distribution and habitat use since 1984.

Methods: Breeding population estimates were made by combining counts of pairs from ‘key sites’ (2?×?2?km tetrads known to be occupied in/since 1984) and estimates of the numbers of pairs away from these sites based on stratified sampling. Survey periods for Little Ringed Plover: 15 April to 15 July, three visits; Ringed Plover: 15 April to 30 June, two visits.

Results: Population estimates, for 2007, of 1239 (95% confidence intervals: 1175–1311) pairs of Little Ringed Plover and 5291 (5106–5478) pairs of Ringed Plovers were calculated for Great Britain, with 5438 (5257–5622) pairs of Ringed Plover estimated in the UK. Counts of Ringed Plover at inland and coastal sites, covered in both 1984 and 2007, decreased by 83% and 53%, respectively. The Little Ringed Plover population has expanded in range northward and westward since 1984. Main habitats used in 2007 by Little Ringed Plover were inland gravel and sand (25.9%) and river shingle (17.8%); and, for Ringed Plover, coastal shingle and sand (38.5% and 13.7%, respectively) and machair plus associated habitats (23.8%) in the Outer Hebrides.

Conclusions: Between 1984 and 2007, the Little Ringed Plover breeding population in the UK increased considerably, expanding northward and westward, with increased use of river shingle habitats. During the same period Ringed Plover breeding numbers in the UK declined considerably in both coast and inland habitats, likely to be due to human disturbance and habitat change, respectively.     

Effect of Sky Lark plots and additional tramlines on territory densities of the Sky Lark Alauda arvensis in an intensively managed agricultural landscape

Capsule: Sky Lark plots and additional tramlines increase Sky Lark Alauda arvensis territory densities in winter crops.

Aims: To analyse the effects on Sky Lark territory density of Sky Lark plots and additional tramlines in winter cereals and oilseed rape.

Methods: We mapped Sky Lark territories on fields with Sky Lark plots or additional tramlines as well as on adjacent control sites, from 2010 to 2013 in Saxony, Germany, where agricultural land use is intensive, dominated by winter-sown crops and takes place in large fields.

Results: In test sites with Sky Lark plots, 5.6 and 3.1 territories per 10?ha were found in the early (April/May) and late periods (June/July) respectively, compared to 3.3 and 1.4 territories per 10?ha in control sites. Sky Lark territory densities in fields with additional tramlines were 1.6 times higher in the early period (4.2 versus 2.6 territories per 10?ha) and 2.2 times higher in the late period (3.6 versus 1.6 territories per 10?ha).

Conclusion: Sky Lark plots and additional tramlines improve large fields for the Sky Lark and have the potential to increase the Sky Lark population.     

Breeding bird populations of Irish peatlands

Capsule Peatlands are very important habitats for birds despite low species diversity.

Aims To describe the variation in breeding bird populations that occur on different types of Irish peatlands and their associated habitat characteristics.

Methods Bird abundance and diversity were compared between four peatland habitat types (fens, raised bogs, Atlantic blanket bogs and montane blanket bogs) at 12 study sites using transects. Various measures of habitat quality were also taken at each location.

Results Only 21 species were recorded during the study, with Meadow Pipit Anthus pratensis and Sky Lark Alauda arvensis accounting for over 80% of all birds recorded. Fens had greater bird species diversity and densities than the other three peatland types. Raised bogs, Atlantic blanket bogs and montane blanket bogs were very similar in terms of their avian diversity. Each of the recorded bird species was associated with different aspects of the peatland habitat.

Conclusion This study shows that despite the relatively low avian species diversity of Irish peatlands, they are of enormous conservation value due to the presence of species of high conservation concern such as Willow Ptarmigan (Red Grouse) Lagopus lagopus and Eurasian Curlew Numenius arquata.     

Estimating the abundance and hatching success of breeding Curlew Numenius arquata using survey data

Counts of individual Curlew and estimates of breeding pairs from ‘field-by-field’ surveys were highly correlated with the numbers of nesting pairs, as determined by intensive studies on 27 sites located on four grassland-dominated study areas. The mean count of individual Curlew over three standard survey visits to each site was used to estimate numbers of nesting pairs. This estimate exceeded the number of nesting pairs on all study areas (as assessed by intensive studies) by 12% but was more accurate than the maximum number of pairs estimated from the three survey visits on each site (the previous convention for estimating breeding pairs). Estimates of the number of pairs hatching chicks were assessed by recording alarm-calling Curlew during late survey visits. The maximum number of alarm-calling pairs was used to estimate the number of pairs hatching chicks, overestimating this by 54%. Three of the study sites were adjacent to extensive moorland which produced overestimates during surveys because moorland nesting birds fed and led broods onto these sites. Omitting these sites from consideration reduced the degree of overestimation to 1% for the number of pairs and 7% for the number of pairs hatching chicks.     

Synergies between site protection and agri‐environment schemes for the conservation of waders on lowland wet grasslands

Two conservation strategies have been put in place in Europe to address precipitous population declines of wading birds that breed on lowland wet grasslands. These are site protection and agri‐environment schemes (AESs) and the two are rarely compared, or their synergy assessed. Increasingly, efforts to recover populations of previously widespread species follow a landscape‐scale approach whereby habitat improvement takes place at key sites through partially overlapping protected area management and AESs. To investigate whether site protection and AESs improve the conservation status of breeding waders and how these interact, we partially repeated a 2002 survey of breeding waders on protected areas (nature reserves and Sites of Special Scientific Interest) and sites with wader‐specific AES options in England in 2009 and 2010. We then assessed the individual and combined effects of these delivery mechanisms on field occupancy, breeding density and population change of four species of declining wader (Northern Lapwing Vanellus vanellus, Common Snipe Gallinago gallinago, Eurasian Curlew Arquata numenius and Common Redshank Tringa totanus). Although results for Curlew differed from the other species, in general field occupancy was positively influenced by conservation delivery mechanisms, with the highest occupancy and breeding densities on land where site protection was combined with wader‐specific AES options. Field occupancy varied between different types of AES, with higher occupancy associated with higher‐level options in fields, particularly those on nature reserves. Outside nature reserves, the history of AES management did not influence wader populations, but within nature reserves and on fields that gained AES management between 2002 and 2009–2010, populations of Curlew and Snipe were more likely to have persisted and population change in Snipe and Lapwing was more positive. We conclude that the conservation of breeding waders will be most effective when site protection and AES management are combined on the same land. Using limited AES money to support management for breeding waders on, around and between the existing network of protected sites will protect remaining populations while presenting opportunities for population expansion in future.     

Numerical and functional responses of Common Buzzards Buteo buteo to prey abundance on a Scottish grouse moor

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.     

Population estimates,trends and habitat associations of breeding Lapwing Vanellus vanellus,Curlew Numenius arquata and Snipe Gallinago gallinago in Northern Ireland in 1999

Capsule Declines in the breeding populations of Snipe, Lapwing and Curlew were recorded between April and June 1999 and compared with previous estimates in 1987.

Aims To compare populations of non-coastal breeding waders between 1987 and 1999.

Methods In 106 2 km × 2 km square tetrads, observers recorded the number of breeding pairs of waders and habitat details on 1:10 000 scale maps.

Results A significant decline of c. 60% for Lapwing and Curlew, and a non-significant decline of 30% for Snipe was recorded over 12 years. Concentrations of these species were found in County Tyrone, but Counties Antrim, Down and Armagh supported few breeding pairs of any species. Very few pairs of any species were recorded on improved grassland despite its widespread availability.

Conclusion A successful conservation strategy for these species must address the wider countryside and not just key sites. Intensive pastoral farming in upland and lowland areas and activities such as drainage and peat extraction will further reduce the suitability of open habitats for these wader species.     

Habitat selection and foraging success of Hen Harriers Circus cyaneus in west Scotland

The foraging behaviour of Hen Harriers breeding in west Scotland was studied in a variety of afforested and moorland habitats. Time budget information from sample areas, stratified by habitat type and controlled for nest distance, was used to investigate habitat selection. Preferences were then related to measures of foraging performance in each habitat. Hen Harriers foraged preferentially over young first rotation coniferous forests, and selected heathland and grassland habitats ahead of closed canopy woodland. Harrier preference for the various habitats was positively correlated with the frequency with which they struck at, and captured, prey. Prey strike success was much lower than that reported for moorland managed for Red Grouse Lagopus lagopus scoticus. The results explain many of the reported changes in local Hen Harrier populations. The extent of young first rotation forestry is currently in decline. It is predicted that this will lead to a reduction in numbers of Hen Harriers breeding in west Scotland, and an increase in the proportion of the British harrier population occupying moorland managed for Red Grouse.     

Varying response of breeding waders to experimental manipulation of their habitat and predators

Many ground-nesting bird species including waders are of conservation concern across Europe. Population declines of Eurasian Curlew Numenius arquata (hereafter Curlew), a globally Near-threatened wader, exemplify this and are driven by low breeding success due to predation, and loss and degradation of breeding habitat. We tested whether the combined delivery of vegetation management and lethal control of Red Foxes Vulpes vulpes and Carrion Crows Corvus corone and Hooded Crows C. cornix improved Curlew nesting success and breeding abundance across UK study sites over five years. On trial sites, vegetation management improved habitat condition and Curlew distributions shifted towards managed areas. However, changes in predator abundances, Curlew nesting success and Curlew breeding abundance did not differ between trial and reference sites. Northern Lapwing Vanellus vanellus numbers increased on trial sites and decreased on reference sites, whilst Common Snipe Gallinago gallinago numbers showed no treatment response. Some of these outcomes were associated with additional environmental variables added to Treatment:Year terms in three-way interactions (changes in fox abundance associated with abundance of non-native gamebirds; changes in Crow abundance associated with gamebirds and woodland area; changes in Curlew nesting success associated with crow abundance), highlighting that outcomes depend on site-specific contexts, and consistent responses to interventions cannot be assumed. The difficulty in increasing Curlew nesting success likely relates to underlying mesopredator densities in the UK, which are known to be high in a European context. Our results suggest that a model of delivery like this study, including management of predators using lethal control, at comparable intensities, is highly unlikely to be effective for Curlew or Snipe within agri-environment schemes, but could be for Northern Lapwing. To make progress on wader recovery it is imperative to understand the underlying drivers of high mesopredator densities and address these through landscape-scale intervention and policy changes.     

Should we account for detectability in population trends?

Capsule?Accounting for changes in detectability over time which could invalidate population trends for common and widespread breeding birds in the UK, resulted in little change in trends for the majority of species considered.

Aims?To examine whether detectability has a significant influence on population trends for common and widespread breeding birds in the UK.

Methods?Using data collected over 16 years of the UK Breeding Bird Survey (1994–2009) and focusing on a random sample of 20 common and widespread bird species, we examine the extent to which controlling for temporal change in detectability would influence national population trends.

Results?Population trends were significantly different for only 2 of the 20 species, Common Blackbird and Winter Wren. This difference corresponds to an apparent fall off in detectability of these species between 2005 and 2009. For the remaining species, controlling for detectability resulted in no significant difference in population trends.

Conclusions?The importance of detectability should be examined as part of any long-term monitoring programme. However, currently we do not find sufficient support for routinely incorporating detectability into population trends for widespread and abundant breeding birds in the UK.     

Predators and nest success of Sky Larks Alauda arvensis in large arable fields in the Czech Republic

Capsule Nest failure owing to a range of predators was high, but the level and specificity of nest depredation cannot be generalised.

Aims To determine fates and predators of Sky Lark nests in conventionally managed arable fields in the Czech Republic.

Methods Sky Lark nests in large fields (mainly Maize, Sugar Beet and Opium Poppy) were monitored by means of continuous video surveillance.

Results Primary nest fates of 42 active nests were fledging (13), depredation (22), desertion (5), nestling death (1), and flooding (1). The overall nest success (Mayfield estimate) was 17% (all mortality factors considered) or 27% (only depredation). Depredation events were caused by Marsh Harrier Circus aeruginosus (11), Hooded Crow Corvus cornix (4), Stone Marten Martes foina (3), Montagu’s Harrier Circus pygargus (2), Red Fox Vulpes vulpes (2), Hedgehog Erinaceus sp. (2) and Eurasian Jackdaw Corvus monedula (1). Successful nests were only slightly more away from field edge than depredated nests; nests taken by birds tended to be closer to field edge than those depredated by mammals. The possible reasons for the absence of a clear edge effect include comparatively large field parcels (about 50 ha) and location of nests far from field edge (median = 195 m).

Conclusion Nest survival and composition of nest predators are site‐specific and contingent upon the study method and may not be simply generalised.     

Native woodland creation is associated with increase in a Black Grouse Lyrurus tetrix population

Capsule: Black Grouse population increases were greatest where new native woodland (NNW) within 1500?m of leks comprised approximately 30% of land area and averaged 5 years old.

Aims: To examine whether change in a population of Black Grouse Lyrurus tetrix in Scotland was associated with the creation of native woodland.

Methods: We examined whether lek location, size and change in size were associated with habitat and topography surrounding leks. We also examined vegetation differences in NNW and adjacent unplanted moorland.

Results: From 2002 to 2012 the number of lekking male Black Grouse increased by 90%. Lek occurrence was positively associated with the amount of NNW edge habitat. Leks were larger where there was more adjacent NNW. Lek increases were greatest where NNW plots comprised approximately 30% land area, and were 5 years old, within a 1500?m radius. Plots aged more than approximately 20 years old were associated with Black Grouse population declines. NNW supported taller and denser important field-layer vegetation than adjacent moorland, likely due to grazing exclusion.

Conclusions: Subject to longer-term management commitments to stimulate continued regrowth of the important field layer and maintain benefits for Black Grouse, expansion of native woodland could contribute to landscape-scale recovery of Black Grouse after decades of decline.     

Breeding phenology and success of the Common Snipe Gallinago gallinago in the Azores

ABSTRACT

Capsule: In comparison to other regions, the Common Snipe Gallinago gallinago in the Azores starts to display earlier and for a longer part of the year, but the laying period, although it starts earlier, does not seem to differ much from that observed elsewhere. Nesting success seems similar to that observed in other populations.

Aims: This study aimed to infer the breeding phenology, characterize some basic breeding parameters, and quantify nesting success in a sedentary, and data deficient population of the Common Snipe.

Methods: Counts of Common Snipe in display (2014) and searches of nests and broods (2011 and 2014) were conducted during the breeding season on São Jorge Island in the Azores. Additional data collected on São Miguel Island was also considered. Nests were monitored to assess nest survival.

Results: The species was seen in display between January and August, and the laying period spanned between early March and late June. The probability of survival during the nesting period was 0.55 (n?=?24; 95% – confidence limits: 0.38–0.80), and desertion was the main cause of failure.

Conclusions: The best period to assess the population of Common Snipe in the Azores is during April, when the displaying activity is at its maximum. The species is very sensitive to disturbance during the nesting and rearing periods, thus managers should avoid interventions in the habitat between March and July to reduce disturbance.     

Effect of climate change on breeding phenology,clutch size and chick survival of an upland bird

Upland birds are predicted to be particularly vulnerable to the effects of climate change, yet few studies have examined these effects on their breeding phenology and productivity. Laying dates of Red Grouse Lagopus lagopus scotica in the Scottish Highlands advanced by 0.5 days/year between 1992 and 2011 and were inversely correlated with pre‐laying temperature, with a near‐significant increase in temperature over this period. Earlier clutches were larger and chick survival was greater in earlier nesting attempts. However, chick survival was also higher in years with lower May temperatures and lower August temperatures in the previous year, the latter probably related to prey abundance in the subsequent breeding season. Although laying dates are advancing, climate change does not currently appear to be having an overall effect on chick survival of Red Grouse within the climate range recorded in this study.