Ron W. Summers

The effects of illegal killing and destruction of nests by humans on the population dynamics of the hen harrier Circus cyaneus in Scotland

Breeding productivity, natal dispersal and survival of hen harriers Circus cyaneus were studied between 1988 and 1995 on moorland managed for sport shooting of red grouse, other heather moorland and young conifer forests in the uplands of Scotland. Nest success was much lower on grouse moors than on other land management classes. Annual productivity was 0.8 fledglings breeding female -1 year -1 on grouse moors compared with 2.4 on other moorland and 1.4 in young conifer forests. Human interference was recorded on half of the grouse moor estates studied and accounted for at least 30% of breeding failures in this land management class. It was much less frequent in the other land management classes. Annual survival of female hen harriers which bred on grouse moors was about half that of females breeding on other moorland. On grouse moors, survival of females which bred unsuccessfully was much lower than that of females which reared at least one fledgling. Survival of breeding females on other moorland was high and unrelated to breeding success. The difference in survival of breeding females between grouse moors and other moors was attributed to killing by humans. On average, 55-74 females were killed each year, 11-15% of the total population of breeding females in Scotland, excluding Orkney. The population of breeding females on grouse moors was estimated to decline rapidly without immigration. Harriers breeding on the other habitats were producing a surplus of female recruits approximately sufficient to compensate for the losses on grouse moors. Most females started to breed at I year old and most males at 2 years old. The percentage of breeding males which were I year old was higher on grouse moors than on the other land management classes. The median natal dispersal distance of both sexes exceeded 10 km. Harriers fledged from one land management class were often found breeding in another. Natal dispersal resulted in net movements of 1-year-old females between land management classes which were sufficient to reduce the differences in population trend which would otherwise have occurred. Moorland managed for grouse shooting was a sink habitat which received two-thirds of its female recruits from other habitats. The difference in productivity and survival between grouse moors and other habitats was attributed to illegal human interference. It is speculated that, without persecution, the hen harrier population in Scotland would increase, initially by about 13% year -1 , until a new, but unknown, equilibrium level was reached.

Microsatellite and mitochondrial DNA homogeneity among phenotypically diverse crossbill taxa in the UK.

Genetic differentiation within and between the three morphologically divergent crossbill species extant in the UK was assessed by comparison of allele frequencies at five unlinked microsatellite loci and DNA sequence variation across the mitochondrial control region. No significant differences in microsatellite allele frequency were found either between different populations of the same species or between the crossbill species themselves. A similar lack of genetic divergence was apparent from the mitochondrial sequence data. We resolved 33 different haplotypes, separated by low levels of sequence divergence (0–0.15%). Levels of divergence within and between species were not significantly different. Haplotypes formed a polyphyletic phylogeny, indicating that the crossbill species do not form genetically separate clades. Discordance between neutral DNA polymorphisms and adaptive morphological variation is discussed in relation to defining the systematic relationship between crossbill forms. If adaptive differences have arisen without a concomitant divergence in neutral DNA then attempting to define crossbill types from microsatellite and mitochondrial DNA without recourse to ecology and behaviour may be misleading.

Habitat selection and diet of the Capercaillie Tetrao urogallus in Abernethy Forest, Strathspey, Scotland

Capsule Woodland characteristics are important for fully grown birds and for broods. Aims To describe habitat selection and diet of the Capercaillie in ancient native pinewoods and Scots Pine Pinus sylvestris plantations, in order to provide a guide for forest management. Methods Tree selection was studied in winter by locating droppings under trees along transects, and comparing those trees used by Capercaillie with those not used. Habitat selection by broods was studied by following radiotagged chicks or females with broods. Diet was described from the analysis of droppings. Results In winter, Capercaillie preferred Scots Pines with wide crowns and large branches, and little surrounding Heather Calluna vulgaris, but avoided forest tracks. Female Capercaillie occurred in stands with a higher density of pines compared to males. The diet of fully grown birds comprised primarily Scots Pine needles between October and April. Scots Pine pollen cones were eaten during May, June and July. Bilberry Vaccinium myrtillus leaves and fruit were eaten in summer and autumn. Habitats used by broods had a higher percentage of Vaccinium sp. and smaller Scots Pines compared with random sites. Chicks hatch at the beginning of June, and in their first two weeks, their diet comprised Formicidae, Lepidoptera larvae and Coleoptera. In July and August, Lepidoptera larvae were rarely eaten but a higher percentage of chicks took vegetable material (particularly Bilberry fruit). In June, smaller numbers of invertebrates were generally trapped in mires of wooded bogs compared with areas of Heather and Vaccinium sp. in old woodland. Areas of Vaccinium sp. had the highest numbers of Formicidae, Coleoptera and Diptera, and especially Lepidoptera larvae. Numbers of Lepidoptera larvae declined during June and July as larvae pupated, explaining the reduction of Lepidoptera larvae in the diet of older chicks. Conclusions Habitat management for Capercaillie should aim to provide old Scots Pine forest with a Vaccinium-rich field layer. Within Scotland, this may entail increasing the tree density in ancient native pinewoods but decreasing it in pine plantations. The removal or closure of tracks might increase the amount of woodland available to Capercaillie, by reducing human disturbance.

Tree and cone selection by crossbills Loxia sp. and red squirrels Sciurus vulgaris at Abernethy forest, Strathspey

Abstract Tree and cone selection by crossbills and red squirrels foraging on Scots pine in winter at Abernethy Forest were described from the distribution of predated cones dropped under trees. Crossbills and red squirrels fed in different parts of the forest. These distributions were related to differences in tree size, shape and density. Crossbills preferred taller, larger trees with broader crowns; these were growing at a low density. In contrast, red squirrels preferred tall trees with short crown depth and growing at a high density. Two hypotheses are put forward to account for tree selection by these species. Selection may be related to predator avoidance. Widely-spaced old trees may provide crossbills with better all-round visibility. In contrast, red squirrels may prefer denser stands where there is less need to come to the ground to cross between trees. Alternatively, crossbills may prefer old, large trees because they have smaller cones. Although smaller cones have fewer and slightly smaller seeds than the larger ones, they still may be more profitable for crossbills because their scales are easier to prise open. Red squirrels are about six times heavier than crossbills and tear or cut into cones with sharp incisors, so probably have less difficulty in opening large cones. The differing preferences for trees and cones by red squirrels and crossbills in native Scots pine forests probably reduces competition, whilst annual fluctuations in the cone crop from area to area may allow the competitively inferior, but more mobile crossbills, to avoid competitive exclusion.

Abundance and distribution of capercaillie Tetrao urogallus in Scotland 1992–1994

Abstract The capercaillie Tetrao urogallus L. is a cryptic forest gamebird which has decreased in Scotland, as in much of its range, since the 1970s. Despite previous surveys of the birds range in Scotland, there was no assessment of numbers giving confidence limits. Here we establish such a baseline against which future estimates may be set. Numbers were estimated from a combination of questionnaires, Geographical Information System (GIS) and advanced line transect techniques, using repeatable methodology which should be applicable to other cryptic forest species. The GIS was used to map capercaillie distribution and relative abundance in Scotland. Transects were then placed randomly within the birds reported range, stratified by geographical region and estimated abundance rating. From observations on 426 2-km line transects in winters 1992–1993 and 1993–1994, the population was estimated to be 2200 birds (1500–3200, 95% C.L.) There were approximately twice as many females as males in the sample. Birds were present from the Forth-Clyde industrial belt northwards to the Dornoch Firth and from the Central Highlands eastwards. The main centres of population were in eastern and central Scotland (Deeside, Speyside and Perthshire). The highest densities were in native pinewoods (2.7–5.0 birds km−2), and the lowest were in thicket and pole/high canopy plantations (0.4–0.9 birds km−2). This information is being used to identify sites for enhancing capercaillie habitat under the Forestry Authoritys Woodland Grant Scheme.

The structure of Abernethy Forest, Strathspey, Scotland

Summary The woodland within the Royal Society for the Protection of Birds (RSPB), Abernethy Forest reserve currently extends over c. 28 km2. One third is plantation and two thirds (c. 19 km2) is native forest, representing one of the largest remnants of the Caledonian forest that once covered much of Highland Scotland. The Scots pine Pinus sylvestris L. is the most abundant tree. Structure was described according to two principal component scores, allowing characterization of the forest into stand types. In the lower, north-west part, plantations and wooded bogs predominate. In the plantations, the treesare younger and grow at a higher density than in the native forest. The upper, south-east section of the forest is composed largely of native pinewood; either old trees with deep crowns growing at a low density or high crown trees at a higher density. Different rates of recruitment, perhaps associated with fire may have led to these two stand types. In the last 100 years, selective felling has exaggerated ...

Capercaillie Tetrao urogallus Nest Loss and Attendance at Abernethy Forest, Scotland

Improvement of breeding success is key to capercaillie Tetrao urogallus conservation in Scotland. However, factors affecting breeding success are not fully understood, including the cause of nest loss. We monitored 20 capercaillie nests with video or digital cameras at Abernethy Forest, Scotland to measure nest loss, determine causes of losses, and describe nest attendance by females. The mean date for the onset of incubation was 15 May and mean clutch size was 7.25 eggs. During incubation, females usually left the nest twice a day (range: 0–4), on average 28 minutes after sunrise and 2 hours 13 minutes before sunset, for a total of 53 minutes per day. There were no egg losses during egg laying, and the daily loss of clutches during incubation (26 days) was 0.0427 (95% CI = 0.0191–0.0663). However, an experiment with artificial nests suggested that predation rates were higher where video cameras were installed than at nests where they were not. After adjusting for the potential effect of deployment of the video system, the daily loss of the capercaillie nests was 0.0205 (95% CI = 0.0074–0.0554). Thus, the probability of a nest failing was 0.68 (95% CI = 0.39–0.83, unadjusted) or 0.42 (95% CI = 0.18–0.77, adjusted). This adjusted estimate at Abernethy Forest was close to the mid-range of other studies of capercaillie nest loss in Scotland and elsewhere in Europe. Eleven of the nests were depredated, nine by pine martens Martes martes and two by unknown predators. One nest was abandoned. Based upon unadjusted daily predation rates, predators destroyed 65% of nests (57% known to be by pine martens) or, after adjusting for the potential effect of the video system, 39% of nests (33% known to be by pine martens). A better understanding of factors affecting pine marten (a protected species in the UK) numbers and hunting patterns is required before a habitat management plan can be implemented to reduce pine marten predation on capercaillie nests.

The structure of ancient native pinewoods and other woodlands in the Highlands of Scotland

A survey was carried out in the Highlands of Scotland of the tree species, tree density, stand structure, and field or ground layer cover in ancient native pinewoods and other woodlands (primarily plantations). The trees in ancient native pinewoods were largely Scots pines but the western sites also had a high proportion of birch. Other woodlands largely comprised planted Scots pine, Sitka spruce, lodgepole pine, larches and Douglas fir. The sizes of the trees were greater in ancient native pinewoods than other woodlands, but some ancient native pinewoods had small trees reflecting recent regeneration or planting. The density of live trees in other woodlands was about 10 times higher than in ancient native pinewoods. The density and percentage of dead trees was also higher in other woodlands. The low density of trees in the ancient native pinewoods has allowed trees to develop deep and broad crowns. The other woodlands were characterised by pre-thickets and thickets. Tree species diversity was greater in other woodlands than ancient native pinewoods. Also, other woodlands had a greater structural variety in terms of stand types, but less variation within stand types, compared with ancient native pinewood. Calluna vulgaris and Vaccinium spp. comprised most of the field layer in the ancient native pinewoods whilst bryophytes, other plants and dead needles made up most of the ground cover in other woodlands. Ancient native pinewoods are generally regarded as biologically richer than plantations, largely due to the differences in stand age and the field layer. However, comparative studies are lacking for many taxa.

Age structure and history of stand types of Pinus sylvestris in Abernethy Forest, Scotland

Abstract Abernethy Forest comprises the largest area of semi-natural (native) pinewood in Scotland. It also has plantations of various ages. This study describes the sizes and ages of Scots pines (Pinus sylvestris L.) in the main stand types as a basis for future management, which aims to develop woodland of natural character. The interpretation of the current age structure is based on historical records of past management [commercial forestry, crofting (subsistence farming) and red deer Cervus elaphus (L.) management for sport shooting] and fires. The main plantation stand types had trees with median ages ranging from 20 to 67 years. The main stand types of semi-natural pinewood (old open, high crown and bog woodland) had median ages of 149, 120 and 126 years and peaks at 121–130, 111–120 and 141–150 years, respectively. The establishment of trees in these stands largely coincided with the removal of crofters and their livestock in 1869, when the upper forest was designated as a sporting estate. This probably allowed a pulse of tree regeneration, before the growing red deer population and pasturing of sheep and cattle inhibited further regeneration through much of the twentieth century. After 1988, sheep and cattle were removed and the number of red deer was reduced, allowing previously suppressed pine saplings to grow. Exploitation for timber over the past 400 years has meant that few trees are over 200 years old. This contrasts with natural Scots pine forests in Fennoscandia where trees typically attain this age, and where the structure is often determined by fire.

Use of time-lapse video cameras to determine causes of nest failure of Slavonian Grebes Podiceps auritus

Capsule Few clutches were predated, with Otter Lutra lutra the most frequent predator filmed. Aims To determine the rate of nest predation and identify predators of the Slavonian Grebe Podiceps auritus in Scotland. Methods Miniature 24-hour time-lapse video cameras were placed next to 23 Slavonian Grebe nests on five lakes to record nest failure events and to identify predators that depredated the contents of nests. For comparison, ten nests without cameras were also monitored and their outcomes recorded. Results The probabilities of clutch failure due to predation, and wave damage or water level rise were 19% and 30%, respectively. Otters took two clutches and an adult grebe plus chicks from nests. Other predators filmed at nests were Stoat Mustela erminea, Carrion Crow Corvus corone, Common Gull Larus canus and Coot Fulica atra. No difference in predation rates between nests with and without cameras was detected. Otters were recorded at eight of 13 lakes studied. An American Mink Mustela vison was recorded at one lake. Conclusion The nest predation rate of Slavonian Grebe in Scotland was not high compared with other studies and is not of conservation concern.