Behavioural responses of non-breeding waterbirds to drone approach are associated with flock size and habitat

ABSTRACT

Capsule: Non-breeding waterbirds are more likely to respond to drone approach when in larger flocks, and responses are more likely in arable and coastal habitats than at inland lochs.

Aims: To investigate the extent to which drones are a potential source of disturbance to non-breeding waterbirds.

Methods: Using a commercially available quadcopter drone, we approached waterbird flocks of varying sizes in coastal, freshwater, and arable habitats following a standardized protocol.

Results: Waterbirds at coastal sites and in arable fields were more likely to respond to drone approach than those at inland freshwater bodies. Larger flocks were more likely to respond to drone approach and responded at a greater distance than smaller flocks.

Conclusion: Repeated drone use at coastal and arable sites with large aggregations of feeding or roosting waterbirds could cause energetically costly flight responses, increased stress, and effective loss of available habitat. At such sites, it may be beneficial to regulate recreational and commercial drone use to minimize potential disturbance effects.     

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.     

The breeding population of Peregrine Falcon Falco peregrinus in the United Kingdom,Isle of Man and Channel Islands in 2014

Capsule: Overall numbers of Peregrines are higher than previously recorded, due primarily to the growth of lowland populations, despite declines in many upland areas.

Aims: To estimate the breeding population of Peregrines, and changes in this population over time, as well as to relate variation in trends and observed breeding success to variation in region, breeding site type and other ecological influences.

Methods: Two types of survey methods were used. Site-based visits focussed on locations where Peregrines were known to have bred previously, while area-based searches aimed to find all Peregrines breeding in randomly chosen 5?km?×?5?km squares. Findings from each method were used to estimate population size in different parts of the survey area. Breeding outcome and site type were assessed for most of the pairs found during either survey.

Results: In 2014, the breeding population of Peregrines in the UK, Isle of Man and Channel Islands was estimated at 1769 pairs. This is 22% larger than the population estimate from the previous survey in 2002. Most of this increase is accounted for by increases in lowland England. Populations in some upland areas have declined.

Conclusions: The gap between the fortunes of lowland and upland Peregrines has continued to grow, along with the overall UK population. Likely reasons for the continued success of Peregrines in the lowlands include increasing uptake of breeding sites on human structures, abundant availability of prey in many lowland situations and, in many areas, a relative lack of conflict with humans. Factors likely to be limiting upland Peregrine populations vary between different regions, and include ongoing illegal killing and deliberate disturbance, and food supply.     

Nest survival of Woodpigeons (Columba palumbus) in North African forests

Capsule The nesting success of the Woodpigeon Columba palumbus in oak forests in Morocco is affected by human disturbance and nest-site characteristics.

Aims To determine factors affecting the nesting success of Woodpigeons subject to two levels of disturbance in a holm oak Middle Atlas forest.

Methods Woodpigeon nests were monitored in highly disturbed (n?=?30) and less-disturbed sites (n?=?60) over two years (2010–11). Logistic-exposure models were used to estimate daily nest-survival rate and evaluate mechanisms (altitude, temporal factors, nest location, nest-site habitat and degree of human influence) affecting nest survival.

Results Daily nest-survival rate was higher in less-disturbed sites (0.987; 95% CL: 0.980–0.991) than in high-disturbance sites (0.967; 95% CL: 0.949–0.978). Increasing density of trees surrounding nest sites and distance from the nest tree to the closest track increased daily nest-survival rate.

Conclusions Less-disturbed sites confer better nesting conditions than highly disturbed ones. Management measures should control the access of vehicles, especially trucks, in the forest of the Middle Atlas and introduce a grazing regime that will allow the forest regeneration, which would improve Woodpigeon nesting success by increasing the density of holm oak trees.     

Waterbird responses to regular passage of a birdwatching tour boat: Implications for wetland management

Participation in outdoor recreation can increase support for wildlife conservation, but may also disturb wildlife. We examined responses of wintering waterbirds to the regular passage of a small boat specifically dedicated to birdwatching tours in a coastal Ramsar site in northern Spain. Disturbances were measured during two separate periods: 2006–2008 and 2012–2015. Incidence and magnitude of disturbance events were compared by grouping species based on their interest to birders (target vs. non-target) and compared across sectors of the tour route. Flight-initiation distances (FID) were used to estimate species-specific buffer zones, which can be used to manage recreational disturbance to waterbirds. We further examined relationships between species-specific traits and FID, time flying, and distance flying following disturbance. A single boat tour disturbed on average 0.3% of non-target and 2.8% of target wintering bird populations within the wetland, with the effect being more pronounced on target species due to their smaller populations. Wing loading was positively associated with distance flying after disturbance. Based on measured FIDs, we calculated an overall buffer zone for all species of 100 m, and species-specific buffer zones ranging from 41 to 211 m. Disturbance incidence and the number of birds disturbed per tour were both greatest in narrow tidal channels (<200 m), where boats were forced to pass within 100 m of waterbirds. We urge caution in allowing boat passage through tidal channels in which boat operators cannot effectively maintain recommended buffer zones between their boat and waterbirds.     

Species‐specific habitat use of wing‐moulting waterbirds in response to temporary flightlessness

The choice of the moulting habitat is of paramount importance for wing‐moulting waterbirds that have to cope with a flightless period of several weeks. However, some species might have more restricted habitat requirements during moult than others, for example due to a highly specialized feeding ecology. The moult‐related habitat use of five species (Gadwall Anas strepera, Red‐crested Pochard Netta rufina, Common Pochard Aythya ferina, Tufted Duck Aythya fuligula, Coot Fulica atra) was compared at a European inland moulting site that offered a variety of water bodies characterized by different levels of nutrient concentration, water depth, shoreline vegetation density and disturbance. To determine location‐ and species‐specific densities, birds were regularly counted throughout the moulting seasons of 2010 and 2011. In 2011, additional data on Gadwalls were used to assess differences in requirements between the flightless phase of moult and the periods before and after. Furthermore, habitat choice of 38 tagged Gadwalls was compared among two to four successive years. During the moulting season, all species showed clear preferences for specific levels of nutrient content, suggesting an active choice of suitable food sources in both food specialists and generalists. Species showing the strongest attachment to shallow water (Gadwall and Coot) were most sensitive to human disturbance and increasing water depths, and species averse to diving (Gadwall) used ponds with dense shore vegetation while flightless. For Gadwalls, habitat conditions rather than nutrient supply became increasingly important during the flightless phase. Average return rates of 59 and 54% were recorded for male and female Gadwalls, respectively, and the repeated use of familiar locations could be demonstrated in the majority of returning birds (65%). Familiarity with the habitat apparently plays an important role and may enable individuals to compensate for suboptimal conditions at the moulting site.     

THE EFFECTS OF PHYSICAL DISTURBANCE ON AFROPTILUM SUDAFRICANUM (EPHEMEROPTERA: BAETIDAE) POPULATION DENSITIES IN A KENYAN MOUNTAIN STREAM

Summary

The effects of physical disturbance on larval populations of the mayfly Afroptilum sudafricanum Lestage were examined in the Naro Morn River, Kenya. Disturbance was induced by stirring, shifting and relocating streambed substrates by hand. The method aimed to simulate natural physical disturbance. The effects of continuous disturbance were examined by sampling larval populations at minute intervals of up to 14 minutes. The effects of periodic disturbance were examined by sampling larval populations which had been disturbed at intervals of minutes (short-term), hours (medium-term) and days (long-term). About 85% of A. sudafricanum individuals was removed from the streambed within four minutes of continuous physical disturbance. There were higher densities at night than during the day. All densities on the control sites for the medium-term disturbance experiments were significantly higher than those on the disturbed sites. Most of the post-disturbance densities on the medium-term disturbance sites were significantly lower than the pre-disturbance densities (Tukey's honestly significance difference test, α=0.05). There was no distinct density pattern on the sites exposed to long-term disturbances. Sites with the same disturbance regime appeared to react differently, some having dramatic fluctuations in density. Disturbance effects on A. sudafricanum density were multi-faceted with different expressions in time and space. It is concluded that A. sudafricanum is highly mobile and is capable of recolonizing disturbed areas within six hours. Their high mobility enables them to crawl into the deeper sediment layers during floods. However, recovery time depended not only on species mobility but also on how densely the sources of recolonization were populated and the frequency of disturbance. Slight increases, strong declines and negligible disturbance effects on the density of A. sudafricanum were evident. Afroptilum sudafricanum is highly mobile and is capable of rapid recolonization. It is concluded that physical disturbance affects A. sudafricanum populations in the Naro Morn River.     

Offshore refuges support higher densities and show slower population declines of wintering Ruddy Turnstones Arenaria interpres

ABSTRACT

Capsule: Wintering Ruddy Turnstones Arenaria interpres occur in higher densities and their populations decline less on, or close to, offshore refuges than on mainland sites subject to greater levels of human disturbance.

Aim: To compare wintering densities of Ruddy Turnstones and changes in counts across time from sites with differing levels of human disturbance.

Methods: Long-term counts of Ruddy Turnstones (1998/1999 to 2015/2016) were used from 19 sites (two offshore refuges and 17 mainland sites subject to higher levels of human disturbance) in northeast England. No direct measure of human disturbance was available for our mainland sites; instead we used questionnaires (n?=?690) to understand how far people travelled to visit the coast and then used this distance with human population densities in a buffer around each site as a proxy for human disturbance levels.

Results: After controlling for the extent of their preferred habitat at each site (rocky shore) we found: (i) the closer each of the 19 sites was to the nearest offshore refuge the higher the density of Ruddy Turnstones and (ii) bird counts were stable at the two refuge sites, whereas, on average, counts declined at the 17 mainland sites. However, no relationship was found between Ruddy Turnstone counts from 17 mainland sites and human population densities within differing distances from each site (up to 10?km).

Conclusions: Our work suggests that Ruddy Turnstones made greater use of relatively undisturbed areas (offshore refuges) than those subject to greater disturbance by humans (mainland sites). Although the use of refuges and mainland in our study area was not well known, observations from 11 radio-tagged Ruddy Turnstones suggest that individual birds did use both locations. In a broader context, our work concurs with other studies that highlight the need for refuges with limited or no human access.     

The first UK survey and population estimate of breeding Snow Bunting Plectrophenax nivalis

Capsule: The first national survey for Snow Bunting Plectrophenax nivalis in the UK was carried out in 2011 and estimated the breeding population at 60 territories (95% confidence intervals?=?48–83).

Aims: To estimate breeding population size for Snow Buntings in the UK by surveying all sites with a history of breeding season occupation.

Methods: Surveys were carried out in June 2011 to detect males on territory at sites where Snow Bunting had been recorded during the breeding season since 1970. Each site was visited at least once during the survey period; suitable habitat was searched and vantage point watches were conducted in order to detect singing males. Repeated visits to a sample of sites allowed a correction factor to be calculated in order to account for birds undetected during surveys.

Results: In 2011, the number of Snow Bunting breeding in the UK (including adjusting for imperfect detection) is a minimum of 60 territories (95% CI?=?48–83) using confirmed and probable breeding records of males. A less conservative estimate of 99 territories (95% CI?=?88–114) results from including all records of males in suitable habitat. The vast majority of the population was found in the Cairngorm region, with isolated records in the north and west Highlands.

Conclusion: The results of the 2011 survey are consistent with well-informed estimates of the Snow Bunting population made previously. This work provides a baseline and repeatable fieldwork and analytical methods enabling future change in the population to be quantified more rigorously.     

Revised estimate of numbers of wintering Red-throated Divers Gavia stellata in Great Britain

Capsule An estimated 17 000 Red-throated Divers winter around Great Britain.

Aim To produce an up-to-date assessment of the numbers of Red-throated Divers wintering around Great Britain.

Methods A revised Great Britain (GB) wintering population estimate for Red-throated Divers was compiled using data primarily from systematic line transect surveys by aircraft over marine nearshore areas conducted during 2001–06, supplemented with county bird records and Wetland Bird Survey (WeBS) counts, both from 1995 to 2005. Population estimates for each survey area around GB were calculated as the mean of either annual means (aerial surveys) or annual maxima (WeBS, county bird records) of all data collected within January and February of each year. These were summed to give a revised GB wintering population estimate.

Results A total of 17116 (13198–21034, 95% confidence interval) Red-throated Divers were estimated to winter around GB. Distribution was uneven. By far the greatest numbers were found off southeast and east Britain (59.3% of the total was between Flamborough Head, Yorkshire, and Dungeness, Kent), with large concentrations off the English south coast (10.9%), north Wales and Liverpool Bay (9.8%), and eastern Scotland (6.1%).

Conclusion This is a minimum plausible population estimate and the true population size may be larger. The new 1% of population threshold for statutory conservation work is 170 birds.     

The breeding status of Peregrine Falcons Falco peregrinus in the UK and Isle of Man in 2002

Capsule Numbers of breeding Peregrines are now higher than ever recorded and the recovery of the species within the UK has continued since 1991.

Aims To estimate the current Peregrine breeding population and its changes over time by recording breeding evidence and nesting range occupancy at known and potential Peregrine eyries.

Methods Attempts were made to check all potentially suitable Peregrine nesting locations for signs of Peregrine occupation. Causes of nest failure were documented where possible. Estimates of occupancy of nesting ranges that could not be visited were based on the proportion of ranges occupied from visited nesting ranges in the same region.

Results In 2002, 1530 Peregrine nesting ranges were estimated to be occupied, comprising 1456 pairs or single birds confirmed as in occupation, and 74 estimated extras (5% of total occupied nesting ranges) that were not visited. Including non‐breeding singletons holding nesting ranges, the UK and Isle of Man figure of ‘Ratcliffe pairs’ was 1437. This showed a 12% increase from 1991 and a 64% increase from the 1930s. However, there were geographical differences in change, with rapid expansion in the south of England tempered by declines in northern Scotland.

Conclusions The primary reasons for the population increase is primarily because of range expansion driven by a plentiful food supply and perhaps an increased tolerance of human disturbance. In areas where the species has declined, various factors (separately or in combination) including reduced food supply and persecution are likely to be involved.     

Response of wetland herbaceous communities to gradients of light and substrate following disturbance by thermal pollution

The influence of thermal disturbance and site characteristics on distribution of herbs was studied in portions of a 3020 ha wetland in the southeastern USA. Presence-absence of 52 species in 130 0.25 m² plots was determined from four sites with different disturbance histories and from an undisturbed site. Data from the four disturbed sites were ordinated by detrended correspondence analysis. Differences in species composition among sites (coarse scale) were associated with water depth, light, and substrate type. Within a site (at a fine scale), correlation of environmental variables with ordination scores at a chronically disturbed site was weakly correlated with light (r=0.50). At two sites with episodic disturbance, species composition correlated significantly and positively with substrate and water depth. At a recovering site, vegetation patterns were moderately correlated with water depth (r=?0.52). Species richness was correlated with substrate type along the disturbance gradient. Our results are consistent the intermediate disturbance hypothesis and the subsidy-stress gradient concept.     

Status of the Hen Harrier Circus cyaneus in the UK and Isle of Man in 2004, and a comparison with the 1988/89 and 1998 surveys

Capsule The population of breeding Hen Harriers in the UK and Isle of Man increased between 1998 and 2004, although country and regional trends differed.

Aims To estimate the size of the UK and Isle of Man Hen Harrier breeding population in 2004, and to compare this with previous estimates made in 1988/89 and 1998.

Methods Surveys were carried out in core and a stratified random sample of 10-km squares throughout the known range, using the same methods as in the 1988/89 and 1998 national surveys.

Results There were an estimated 806 territorial pairs in the UK and Isle of Man in 2004, a significant 41% increase from the 1998 estimate of 570 pairs. Increases were found throughout, with the exception of south and east Scotland and England, where numbers decreased. Scotland held 79% of the UK and Isle of Man breeding population in 2004, and 10% of Scottish pairs were associated with non-moorland habitats, such as mature conifer plantations and scrub/brash.

Conclusions There was a substantial increase in the breeding population in most regions of the UK and Isle of Man between 1998 and 2004, possibly aided by increased use of non-moorland habitats. However, populations declined in upland areas of southern and eastern Scotland and northern England. Continuing illegal persecution arising from perceived conflicts between breeding Hen Harriers and driven grouse shooting may be a major cause of these regional declines.     

Hunting and the fate of French breeding waterbirds

Capsule French breeding populations of hunted waterbirds have more negative long-term population trends than closely related non-hunted species.

Aims To assess the relative fate of breeding populations of hunted and non-hunted waterbird species in France.

Methods We compared long-term population growth rates of hunted versus non-hunted waterbirds using two large-scale and long-term national surveys.

Results Waterbirds globally displayed long-term increases in population sizes most likely driven by their positive response to the implementation of numerous protected areas over remnant wetlands across the country since the early 1970s. In contrast, hunted species revealed more negative trends compared to non-hunted species.

Conclusion A causal relationship between hunting and population dynamics is not demonstrated here, but the results are consistent with species' breeding populations being negatively affected, on average, if they are hunted.     

Status of the Hen Harrier Circus cyaneus in the UK and Isle of Man in 2016

Capsule: The fifth UK and the Isle of Man survey of Hen Harrier in 2016 showed varying trends by country and region.

Aim: To estimate the size of the breeding Hen Harrier population (with associated 95% confidence intervals) in the UK and Isle of Man, constituent countries and Scottish regions, in 2016 and calculate population change over the five surveys to date.

Methods: Complete surveys were made of all 10-km squares likely to be occupied by breeding Hen Harriers in England, Wales, Northern Ireland and the Isle of Man, using standard methods developed for previous national surveys. In Scotland, self-selected 10-km squares were surveyed by volunteers and a stratified random selection of the remaining 10-km squares within the known breeding range was surveyed.

Results: The UK and Isle of Man Hen Harrier population was estimated at 575 territorial pairs (95% confidence limits, 477–694), a non-significant decline of 13% since 2010 but a significant decline of 24% since 2004. Scotland held the majority (80%) of the population with 460 (359–573) territorial pairs. Elsewhere, 46 territorial pairs were recorded in Northern Ireland, 35 in Wales, 30 in the Isle of Man and four in England. Significant decreases were recorded in the number of pairs in Scotland using grouse moor (?57%) and young forest (?54%).

Conclusion: The combined breeding population of Hen Harriers in the UK and Isle of Man has shown a non-significant decline between 2010 and 2016. There were notable decreases in England, Northern Ireland and Wales since 2010.     

Species turnover of monkey beetles (Scarabaeidae: Hopliini) along environmental and disturbance gradients in the Namaqualand region of the succulent Karoo, South Africa

Species turnover of monkey beetle (Scarabaeidae: Hopliini) assemblages along disturbance and environmental gradients was examined at three sites within the arid, winter rainfall Namaqualand region of the succulent Karoo, South Africa. At each site two study plots with comparable vegetation and soils but contrasting management (grazing) histories were chosen, the disturbed sites having fewer perennial shrubs and generally more annuals and bare ground. Beetles collected using coloured pan-traps showed a consistently higher abundance in disturbed sites. Lepithrix, Denticnema and Heterochelus had higher numbers in disturbed plots, while Peritrichia numbers were lower in disturbed areas. Measures of species richness and diversity were consistently higher in the undisturbed sites. Distinctive assemblages of monkey beetles and plants occurred at each site. A high compositional turnover ( diversity) was recorded for both monkey beetles and plants along a rainfall gradient; between-site diversity values ranged from 0.7 to 0.8 (out of a maximum of 1.0). Species turnover of beetles was higher between the disturbed sites along the environmental gradient than the corresponding undisturbed sites. The high monkey beetle species turnover is probably linked to the high plant species turnover, a distinctive feature of succulent Karoo landscapes. Monkey beetles are useful indicators of overgrazing disturbance in Namaqualand, as their pollinator guilds are apparently disrupted by overgrazing. A shift away from perennial and bulb pollinator guilds towards those favouring weedy annuals was observed in disturbed areas. The consequences to ecosystem processes due to the effects of disturbance on monkey beetle communities and the role of monkey beetles as indicators of disturbance is discussed, as well as the implications of disturbance on monkey beetle pollination guilds.     

Key sites for the conservation of waterbirds in Uganda

Arinaitwe, J., Byaruhanga, A. & Mafabi, P. 2000. Key sites for the conservation of waterbirds in Uganda. Ostrich 71 (1 &2): 102–105.

Uganda has a rich bird diversity with 1 008 species including 28 listed species (Collar et al. 1994) and 207 species of regional conservation concern (Bennun & Njoroge 1996). Over 240 species are waterfowl, of which nine are globally threatened, 45 are regionally threatened and five are considered to be of national conservation interest. This high waterbird diversity corresponds to a large wetland area covering about 10% of the land area of Uganda. However, only 6% of the wetlands fall under gazetted protected areas and only one site is recognised as of global importance under the terms of the Ramsar Convention. Three recent activities of JA, the National Wetlands Programme and East Africa Natural History Society (Uganda), have produced new information on distribution and abundance of waterbirds in Uganda. Concurrent with these activities, criteria for the identification of globally threatened species (Collar et al. 1994), species of regional conservation concern (Bennun & Njoroge 1996) and nationally important species (National Wetlands Programme, in press) have been developed. Also, criteria for selection of sites at the global (Ramsar and IBA), regional (IBA) and national (National Wetlands Programme) levels have become available. This paper reviews the advances in the knowledge of waterbirds in Uganda and applies the above criteria to highlight sites that are crucial for conservation at global, regional and national levels.     

Factors affecting reproduction of Woodpigeons Columba palumbus in North African forests: 1. Nest habitat selection

Capsule Woodpigeon Columba palumbus nest-tree selection is affected by human disturbance, grazing and tree characteristics.

Aims To determine the characteristics of trees used for nesting by Woodpigeons under two levels of grazing and disturbance in a Holm oak Middle Atlas forest, Morocco.

Methods Woodpigeon nest-tree selection was investigated in highly disturbed and less-disturbed sites over two years (2010 and 2011). The features of nest-tree characteristics were determined by comparing the characteristics of trees used for nesting to those of randomly selected trees.

Results Tree physical characteristics, grazing intensity and level of human disturbance were the main factors determining selection for nest-trees. Woodpigeons chose nesting trees that were greater in height, larger in DBH, lower in base of the live crown, in denser stands and at greater distance from tracks.

Conclusions Forest management for Woodpigeon nest habitat selection should focus on controlling the access of vehicles especially trucks, introducing a rotating system of forest utilization for grazing and maintaining (without extending) the cereal crops. These recommendations may assist land managers to plan for continued persistence of this species in Middle Atlas forests.     

Effects of human disturbance on the diet composition of wild red deer (Cervus elaphus)

Disturbance from human recreational activities may affect the nutrition of free-ranging herbivores due to trade-offs between feeding in preferred habitats and perceived predation risk. To test this hypothesis, we estimated diet composition for red deer in the Scottish highlands in spring, when recreational activity tends to be high, and in winter when it is lower. We analysed faecal samples from three habitat types (grassland, heather moorland and woodland) collected at sites close to a busy track (disturbed) and at a distance from it (less disturbed). The diet consisted of 39% grasses, sedges, herbs and rushes (GSHR) and 58% Calluna vulgaris and Erica spp. (heather) in spring, compared with 14% grasses and 77% heather in winter, with small quantities of Vaccinium spp. (berry) and Pinus sylvestris (tree) in both seasons. In spring, faeces from disturbed grass and woodland sites indicated a diet with less GSHR and more heather and tree than faeces from less-disturbed sites, which could be due to an increased need for vigilance in exposed grassland and the need to seek cover. In contrast, faeces from all disturbed sites in winter indicated a diet with more GSHR and less heather than faeces from less-disturbed sites. This could be due to a seasonal decline in recreation and increase in hunting activity reversing the disturbance levels at the different sites, since hunting is not normally carried out in areas used by the public for recreation. We conclude that there may be nutritional benefits to deer of reducing disturbance near open grassland.     

The status of the Hen Harrier,Circus cyaneus,in the UK and Isle of Man in 2010

Capsule The fourth national survey of Hen Harrier showed that the population in the UK and the Isle of Man declined significantly between 2004 and 2010.

Aim To estimate the size of the breeding Hen Harrier population (with associated 95% confidence intervals) in the UK and Isle of Man, constituent countries and Scottish regions, in 2010 and calculate population change since previous surveys in 1998 and 2004.

Methods Complete surveys were made of 10-km squares likely to be occupied by breeding Hen Harriers in England, Wales, Northern Ireland and the Isle of Man, using standard methods developed for previous national surveys. In Scotland, a ‘census’ area was non-randomly selected for survey by volunteers, and randomly selected squares were surveyed in two strata covering the rest of the known range.

Results The UK and Isle of Man Hen Harrier population was estimated at 662 territorial pairs (95% confidence interval (CI): 576–770), a significant decline of 18% since 2004. Scotland holds the bulk (76%) of the population (505 territorial pairs; 95% CI: 417–612), with smaller numbers in Northern Ireland (59 pairs), Wales (57 pairs), the Isle of Man (29 pairs) and England (12 pairs). Declines of 49% and 20% were observed in the Isle of Man and in Scotland, respectively, whereas the Welsh population increased by 33%. A significant decrease was recorded in numbers of pairs using young and mature plantation forest in Scotland.

Conclusion The breeding population of Hen Harriers in the UK and Isle of Man declined between 2004 and 2010. Notable decreases in Scotland and the Isle of Man may be related to habitat change and illegal persecution. Illegal persecution continues to limit the population size of harriers in England to very low levels.