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.     

THE FIRST ALFRED NEWTON LECTURE Presented at the "Bird Conservation in Action" conference, April 1994

The breeding densities of birds could be limited by resources, such as food and nest sites, or they could be held at a lower level by natural enemies, such as predators and parasites. In this paper, I review the experimental evidence for each of these limiting factors affecting bird breeding densities. Of 18 experiments involving winter food provision (mostly on tits, Paridae). 11 led to increased breeding densities compared with control areas. Of four involving summer food depletion (all on forest insectivores), none led to decreased breeding densities. In experiments with Red Grouse Lagopus 1. scoticus , fertilizing areas of heather moor led to increased densities during a period of population increase but did not prevent a later decline. Of 32 studies on tree-cavity nesters, the provision of nestboxes led to increased breeding density in 30 (95%) studies, each involving one or more species of hole nesters. Of 15 experiments involving predator removal (mostly on ducks and gamebirds), at least 14 led to increased hatching success, four out of eight led to increased post-breeding numbers, and six out of 11 led to increased breeding density. In one experiment, the removal of strongyle parasites from a Red Grouse population prevented a cyclic decline on five out of five occasions. Taken together, these experiments confirmed that all main potential external limiting factors have affected breeding density in one bird species or another. They also confirmed that the same species has been limited by one factor in certain areas or years and by another factor in different areas or years.     

Factors influencing red deer occurrence at the southern edge of their range: A Mediterranean ecosystem

The red deer is in the Iberian Peninsula at the southwestern edge of its European range and although widespread, red deer ecology in Portugal remains poorly understood. By using pellet group counts, we investigate how habitat structure, vegetation composition and human disturbance affect red deer occurrence. Red deer distribution was positively associated with areas with high density of heather, Leguminosae plants and patches with high cover of shrubs, ground cover and tree cover. Red deer occupied areas further away from roads and from villages. Red deer distribution was negatively associated with agricultural fields and areas with high canopy cover.In the perspective of the current climatic changes, continue research on red deer in these so-called edge populations represents an opportunity to assess the ecological responses within an evolutionary perspective and to provide important conservation suggestions for other countries located on the edge of its distribution range. The present results have implications for the conservation of red deer, emphasizing the need for wide range ecological studies. Red deer variation seems to be related to local factors rather than proximity to the edge of its range.     

The habitat use and diet of Black Grouse Tetrao tetrix in the Pennine hills of northern England

The habitat and dietary preferences of Black Grouse were studied from 1989 to 1991 in a largely treeless habitat within a 17 km² area of the Pennine hills of northern England using radiotelemetry. Grassland habitats were preferred by 84% of 19 birds for much of the year and heather moorland was selected in winter; the other birds, all females, remained in heather habitats all year. Most females reared broods in damp, rushy grass moorlands, but one of six broods used hay fields. Diet closely reflected seasonal plant availability in selected habitats and the leaves, flowers, fruits and seeds of a wide variety of plants were eaten. Cotton-grass Eriophorum vaginatum was important in spring, grassland herbs, grasses, sedges and rushes in summer and autumn and Ling Heather Calluna vulgaris in late autumn and winter. Males fed substantially more on heather in winter than females which partially replaced heather in their diet with the leaves of grasses and herbs. Young chicks showed considerable preference for Sawfly (Symphyta) larvae. Suggested management recommendations include the regulation of sheep-grazing, encouragement of wet flush areas and the late cutting of hay fields.     

Utilisation of different ages of heather on three Scottish moors by red grouse, mountain hares, sheep and red deer

Utilisation of heather at three Scottish moors, by red grouse, mountain hares, sheep and red deer, was measured by collecting their faecal droppings regularly from plots on heather patches of different ages. Rates of heather growth differed between moors, and preferences of the four species, all grazers of heather, were related more closely to its height than to its age. Thus hares spent most time on ground with heather less than 15 cm high, sheep less than 20 cm, grouse preferred heather 10–30 cm high and deer spent most time on heather over 25 cm high.
Differences between outer, middle and inner plots on patches at one of the moors in dicated that grouse are reluctant to move far from cover into areas of newly burned ground, and reluctant to move far into patches of tall, dense heather, when these are next to shorter material. Hares preferred the middle of patches on newly burned ground and very young heather.
At two of the moors, but not the third, there was evidence that heavy grazing by hares in winter reduced the amount of young heather available to hares and grouse in spring. This potential reduction in the quality of the spring diet of grouse is discussed In relation to previously reported associations between numbers of hares and grouse at those two moors.     

莲花山斑尾榛鸡春季栖息地选择

20 0 3年 3～ 4月 ,在甘肃省莲花山自然保护区 ,利用无线电遥测和直接观察 ,分析了斑尾榛鸡(Bonasasewerzowi)的栖息地选择特征。结果表明 ,斑尾榛鸡春季栖息地一般在东北坡向 ,并具有高大乔木、下层植被盖度较高、灌丛较丰富的特点 ,这与食物丰富度较高及环境隐蔽性较强有关。栖息地质量对于配对活动的成功与否有一定影响。分析表明 ,栖息地内 0 5～ 2 5m植被水平遮挡度、柳树数量、箭竹数量是影响斑尾榛鸡春季栖息地选择的关键因子。建议在对斑尾榛鸡栖息地采取保护措施时 ,不仅要保护原生乔木 ,还要加强对灌丛生境的保护。     

Regional Synthesis of Habitat Relationships in Shrubland Birds

Abstract: Shrubland birds are declining throughout the eastern United States. To manage scrub-shrub habitats for birds, managers need information on avian habitat relationships. Past studies have produced contradictory results in some cases and may be of limited generality because of site- and habitat-specific factors. We studied shrubland birds across 6 habitats in 3 New England states to provide more general information on habitat relationships than has been possible in past studies. Our study sites included all major scrub-shrub habitats in New England: wildlife openings, regenerating clear-cuts, beaver ponds, utility rights-of-way, pitch pine (Pinus rigida) woodlands, and scrub oak (Quercus ilicifolia) barrens and ranged from Connecticut to northern New Hampshire, with research conducted from 2002 to 2007. Using N-mixture models of repeated point counts, we found that 6 of 12 shrubland birds preferred areas with greater shrub cover. An additional 4 species appeared to prefer areas with lower-stature vegetation and greater forb cover. Eight of 10 bird species showed relationships with cover of individual plant species, with Spiraea spp., willows (Salix spp.), alders (Alnus spp.), and invasive exotics being the most important. We recommend that shrubland management for birds focus on providing 2 distinct habitats: 1) areas of tall (>1.5 m) vegetation with abundant shrub cover and 2) areas of lower (<1.5 m) vegetation with abundant forb cover but fewer shrubs.     

Effects of vegetation on nest microclimate and breeding performance of lesser black-backed gulls (Larus fuscus)

For birds that breed in large colonies, the overall area occupied by the colony generally comprises several sub-areas that differ in physical and social features such as vegetation and breeding density. Birds arriving at a breeding colony select their nesting sites through a hierarchical process of selecting a sub-area, then a particular nest site with appropriate biotic and physical attributes. Optimal vegetation cover is one such important attribute. Many ground nesting gulls preferentially select nest sites that provide shelter during reproduction, but this presumably has to be balanced against any costs such as reduced visibility of potential predators. The effects of vegetation height in the sub-areas within a colony, and of the amount of vegetation in the immediate vicinity of the nest on nest microclimate were investigated in lesser black-backed gulls Larus fuscus in a colony in which overall vegetation height differed in different sub-areas and was patchily distributed within these areas. Tall vegetation did have a sheltering effect, and this was positively related with chick growth. However, this vegetation area was associated with lower breeding densities, relatively late laying birds and lower chick survival rate, suggesting that sub-areas with tall vegetation held more lower-quality or young breeders. Within the sub-areas, the birds preferentially selected nest sites with more surrounding vegetation, and this was positively correlated with their hatching success.     

Seasonal use by birds of stream-side riparian habitat in coniferous forest of northcentral British Columbia

To determine use of riparian habitats by birds in the northern coniferous forest of British Columbia, we censused birds and vegetation along 500 m transects placed parallel and perpendicular to three second-order streams. Censuses were conducted during spring, summer, autumn, and winter to investigate how use of riparian habitat changed seasonally. Stream-side riparian zones were characterized by a dense understorey of deciduous vegetation not found in the upslope forest. Nine bird species preferred the riparian understorey for breeding, six preferred it only during migration. Neotropical migrants (16 of 46 species) were more closely associated with stream-sides than year-round residents (11 species). Some breeding birds (five species) were significantly negatively associated with riparian habitats. The density of riparian birds declined with distance upstream but did not decline up to 250 m away from the stream. The more extensive riparian areas downstream supported a greater density of birds in all seasons compared to upstream areas, but more species only in spring and autumn. Species that nested in non-riparian areas in summer used riparian habitat in autumn, making riparian corridors in the northern coniferous forest important during migration. Maintaining both riparian and upslope habitats is necessary to preserve species diversity al the landscape level.     

Dispersal distances of juvenile radiotagged Red Grouse Lagopus lagopus scoticus on moors in northern England

Radio-transmitters were fitted on 146 juvenile Red Grouse Lagopus lagopus scoticus (116 hens, 30 cocks) to study the timing, frequency and distances of dispersal on managed grouse moors in northern England between 1999 and 2002. A third of the radiotagged birds were shot. Disturbance on shoot days meant that radiotagged birds were shot at points more than twice as far from the catch location as the points when they were last recorded alive. For birds that were shot, the distance from the catch location to the place they were shot was more than twice the natal dispersal distances of the survivors. Therefore, shot birds were excluded from the dispersal analysis. Juvenile hens dispersed significantly further (mean 861 m, range 50–4660 m) than juvenile cocks (mean 343 m, range 90–660 m). Dispersal distances were not related to predispersal Grouse densities at the catch area in summer or to Grouse densities in the following spring. The mean date of dispersal for juvenile hens was 6 October ± 4 days (se), with only one record of spring dispersal (14 March) of 1490 m.     

Hen Harrier Circus cyaneus foraging activity in relation to habitat and prey

Capsule In west Scotland, the birds foraged in accordance with the distribution of prey and vegetation associated with early-growth conifer forests.

Aims To investigate foraging Hen Harrier activity in relation to vegetation cover and structure and the abundance of potential prey.

Methods Forty 1 × 1-km sample observation areas were monitored at four sites in west Scotland.

Results Foraging time in the sample squares was dependent on the proximity of harrier nests. Harriers preferred areas with relatively high densities of Field Voles Microtus agrestis and Meadow Pipits Anthus pratensis, associated with tall ground vegetation and shrub layers. They also preferred areas planted with trees but preference declined with increasing tree foliage 2–5 m tall and bare ground.

Conclusion Conifer forests can provide favourable conditions for foraging harriers during the early growth stages. Further work is required to determine the value of other types of woodland.     

The diurnal habitat used by red deer (Cervus elaphus L.) in the Haute Ardenne

We describe diurnal habitat used by red deer (Cervus elaphus L.) in two representative forests of Haute Ardenne. We captured 17 calves and 13 adults and fitted them with VHF transmitters (ear tags or collars). Each animal was radio-tracked at least once per week during the daylight hours and relocated by triangulation. To determine habitat use, we used compositional analysis. We defined use for each animal as the proportion of relocations in each vegetation association. Each relocation was weighed according to its accuracy (i.e., based on the confidence ellipse computation). We defined availability as the proportion in the area of each vegetation association within its home range (i.e., minimum convex polygon). Red deer calves preferred edges in open areas (e.g., clear-cuts) during their first 3 months of life. Adults used open coniferous [e.g., natural regeneration of spruce (Picea abies)] stands and edges between coniferous stands and other vegetation associations. Closed coniferous stands were preferred during winter and deer usually used the edges of habitat patches rather than the core areas, except in winter for coniferous stands. The deciduous stands [e.g., old growth stands of beech (Fagus sylvatica)] were usually avoided, except in winter when the edges of deciduous stands were used. The availability of coniferous stands and edges partly determined the size of the diurnal home ranges.     

Seasonal differences in habitat selection by Black Grouse Tetrao tetrix in the northern Pennines, England

Between-season differences in habitat use by Black Grouse Tetrao tetrix were studied on four moors in the northern Pennines between 1989 and 1992. Heather moor and bogs were preferred at all times of the year, apart from during the breeding season. In spring, large quantities of Cotton-grass Eriophorum vaginatum flowers were consumed, whereas in autumn and winter Heather Calluna vulgaris was more important. Enclosed fields on the edge of the moors were regularly used in autumn and winter by large flocks of cock birds, and hens were found in smaller groups. Where present, overgrazed grass moorland was generally avoided, apart from during the summer. Similarly, enclosed rough grazing allotments rich in rushes were favoured during the summer months by breeding hens and moulting cocks.     

Restoration of Wetlands from Abandoned Rice Fields for Nutrient Removal, and Biological Community and Landscape Diversity

A number of experimental freshwater wetlands (150 m long × 75 m wide) with different ages since they were abandoned as rice fields, were used to analyze the prospects of multipurpose wetland restoration for such degraded areas. Nitrogen and phosphorus removal rate of the wetlands were determined monthly during the flooding season to estimate their efficiency as filters to remove nutrients from agricultural sewage. The number of wetland birds was recorded regularly to identify their habitat preferences. Both the temporal dynamics and changes in the spatial pattern of land use cover during the last 20 years were determined from aerial photographs and field analysis. All the wetlands appeared to be very efficient in the removal of nitrogen and phosphorus exported from rice fields. Usually 50–98% of the nitrogen and less than 50% of the soluble phosphorus were removed by the wetlands at any stage of restoration. Wetland birds preferred wetlands with intermediate plant cover for resting and sleeping activities better than rice fields and either very open wetlands or very dense ones with tall vegetation. Apart from the improvement in water quality and the restoration of natural habitats, restoration of wetland belts around lagoons will increase spatial heterogeneity and diversity of the landscape.     

Predation risk of artificial ground nests in managed floodplain meadows

Nest predation highly determines the reproductive success in birds. In agricultural grasslands, vegetation characteristics and management practices influences the predation risk of ground breeders. Little is known so far on the predation pressure on non-passerine nests in tall swards. Investigations on the interaction of land use with nesting site conditions and the habitat selection of nest predators are crucial to develop effective conservation measures for grassland birds.In this study, we used artificial nests baited with quail and plasticine eggs to identify potential predators of ground nests in floodplain meadows and related predation risk to vegetation structure and grassland management.Mean daily predation rate was 0.01 (±0.012) after an exposure duration of 21 days. 70% of all observed nest predations were caused by mammals (Red Fox and mustelids) and 17.5% by avian predators (corvids). Nest sites close to the meadow edge and those providing low forb cover were faced with a higher daily predation risk. Predation risk also increased later in the season. Land use in the preceding year had a significant effect on predation risk, showing higher predation rates on unmanaged sites than on mown sites. Unused meadows probably attract mammalian predators, because they provide a high abundance of small rodents and a more favourable vegetation structure for foraging, increasing also the risk of incidental nest predations. Although mowing operation is a major threat to ground-nesting birds, our results suggest that an annual removal of vegetation may reduce predation risk in the subsequent year.     

Habitat characteristics of Eurasian pine martens Martes martes in an insular Mediterranean environment

Eurasian pine martens are considered habitat specialists, associated primarily with mature stands of mesic mixed wood forest habitats, and avoid areas without overhead cover The species is found throughout the temperate and boreal regions of the continent but on the Mediterranean island of Minorca, introduced pine martens thrive in a competitor- and predator-free environment I test the prediction that because of evolved prey-capture and predator avoidance strategies Minorcan martens should select habitats most similar to temperate and northern parts of their range Scat index routes were used to quantify pine marten habitat selection Marten did not demonstrate any habitat type preferences although observed use of pine forests and coastal shrublands was slighly greater than expected Marten were indifferent to overhead cover whereas mesic sites and areas of tall high shrub density were favored Small mammal trap indices and preferred prey suggested that martens commonly used non-forested areas My results demonstrated that on Minorca pine martens were habitat generalists In the absence of predators open non-forested habitats were equally important to pine marten as were forested ones     

Designing Timber Harvesting to Enhance New Zealand Falcon Populations

Previous breeding-season studies of threatened New Zealand falcons (Falco novaeseelandiae) in plantation forests have suggested that falcons benefit when harvesting creates a mosaic of differently aged stands, especially where young and mature tree stands are adjacent. Thus, changes in the rate and pattern of harvesting may affect habitat heterogeneity by altering the size and distribution of forest patches. We sought to determine guidelines for harvesting that would most benefit falcons by increasing the carrying capacity of the forest for falcons. We used radio-tracking to determine the home-range sizes of non-breeding falcons over 3 seasons and compared winter home-range overlap in the most-selected land cover types by falcons (mature-young edges and open patches) with other land cover types. The distribution of open patches and edges between mature stands and recently cleared areas affected falcon home ranges, home-range overlap, and the likelihood of nesting. Specifically, home ranges were smaller as the density of edges and percentage of open patch increased, and there was greater home-range overlap between individuals in the most-selected land cover types. Numbers of falcons decreased as the size of open patches increased, concomitant with a decrease in edge size, the number of edge borders, and the number of open patches. The likelihood of nesting also decreased as open patch size increased. Our results indicate that smaller open patches spread through a forest, maximizing the amount of mature-young edges, will favor smaller home ranges and therefore potentially greater numbers of falcons. We recommend harvesting protocols that ensure that open patches (0–3-yr-old stands) are <4 km² in size and retain at least small stands of mature pine to maintain a high density of edges. Similar protocols may increase the carrying capacity for other species occurring in managed systems involving fragmented landscapes or small reserves. © 2021 The Wildlife Society.     

Satellite monitoring of the state of forest vegetation after fire impacts in the Zabaikal region

Based on the MODIS radiometer data, the level of disturbance of forest lands by fires has been estimated for southwestern areas of the Zabaikal region. A combined analysis of vegetation indices calculated by measuring reflected radiation in the near and mid-infrared wave ranges and the data of on-ground studies allowed us to identify sites with successful and poor reforestation. Based on the instrumental data, it is found that repeated fires prevent successful reforestation. An analysis of seasonal dynamics indicates that summer fires result in greater damages of forest vegetation than those caused by spring fires. Larch stands prevailing in the region cover the largest portion of fire-disturbed lands (and the largest area, where reforestation processes are hampered), while pine and deciduous stands are characterized by a higher frequency of fires.     

Nest-site selection by crossbills Loxia spp. in ancient native pinewoods at Abernethy Forest,Strathspey, Highland

Capsule Birds preferred stands with a particular density of trees, perhaps to avoid predation, and they selected aspects sheltered from prevailing winds.

Aim To describe the nesting habitat and tree selection by crossbills in a restricted pinewood habitat in Scotland.

Methods Scots Pines used by nesting crossbills were described and compared with randomly selected pines. Nest aspect was related to wind strength and direction.

Results The crossbills selected trees at a density of 50–60 trees/ha. Such stands may be sufficiently dense to provide cover, yet occur at a low enough density to minimize being visited by potential arboreal predators, such as Red Squirrels and Pine Martens. Crossbills tended to nest on lateral branches on the northeast side of crowns. Tree crown development was not asymmetric, so the birds may choose the northeast side to shelter from the prevailing southerly to westerly winds.

Conclusion Stands of pines at a low density need to be maintained for the benefit of crossbills.     

THE FOOD OF RED GROUSE CHICKS LAGOPUS L. SCOTICUS

The diet of young Red Grouse was studied from the crop contents of 211 chicks caught on a moor in northeast Scotland. The food was more varied than that of adults, but shoot tips of heather usually formed at least 75% (by dry weight) of their diet, as in adults. Arthropods, particularly Diptera, were taken frequently by chicks up to three weeks old, but they formed less than 5% (by dry weight) of the diet then. The chicks ate more invertebrates when more were available. There was no evidence that chick survival was related to the abundance of invertebrates. The chicks ate heather containing more nitrogen and phosphorus than that eaten by adults at the same time of year.