Interactions between harvesting, noise and territoriality in a model of red grouse population cycles

In a recent paper in Journal of Animal Ecology, Laurenson et al. (2003) used an unreplicated experimental reduction in mountain hare (Lepus timidus Lath) numbers to test the importance of mountain hares in the persistence of louping-ill in a red grouse (Lagopus lagopus scoticus L.) population at a site in Morayshire. Their results confirmed that mountain hares are an important host of the sheep tick (Ixodes ricinus L.), and a vector of the louping-ill virus. They go on to show that a reduction in hare density was coincident with a reduction in tick numbers, a reduction in louping-ill seroprevalence in grouse and an increase in grouse breeding success. They concluded that, in the presence of mountain hares, ‘it may not be possible to take large harvests of red grouse’, and make moorland management for grouse uneconomic. Their case for mountain hares being important in the persistence of louping-ill is weakened by the lack of a rigorous experimental design but, moreover, they have failed to demonstrate that the removal of mountain hares has any effect on the potential harvest of red grouse, making their conclusions unreliable. We argue that the impact of louping ill on grouse dynamics, and the role that hares play in this, needs further investigation before any firm conclusions can be drawn or recommendations made for grouse-moor management with respect to the culling of mountain hares. Laurenson et al. set out to ‘test whether a reduction in hare densities leads to a decline in tick and louping-ill virus populations’. The authors acknowledge that an unreplicated treatment was not a satisfactory way to conduct such a test, but we would add that the problems associated with the lack of replication were increased by the absence of proper controls. The difference between a control site and a treatment site should be only in the treatment itself, with all other factors kept the same. In any large-scale field experiment, the choice of suitably paired sites is difficult, if not impossible, as sites will always differ in a variety of biotic and abiotic conditions, some of which may be very important. Both the control sites in this study are examples of just this problem: Control site 1, in Perthshire, was used for comparisons of louping-ill seroprevalence, and tick burdens in the red grouse population. Laurenson et al. stated that ‘tick numbers on grouse chicks decreased significantly on the treatment site between 1992 and 2001 in comparison to the control site’; and that ‘there was a significant reduction of louping-ill virus prevalence at the treatment site in comparison to the control site’. However, the management of this control site changed partway through the study, as the mountain hare culling regime changed in 1999. Louping-ill prevalence at control site 1 was also much lower than the treatment site even though the tick density was higher than the treatment site for much of the study period, suggesting that there were factors other than mountain hares involved in the relationship between tick numbers and louping-ill prevalence in red grouse. To look at the effect of mountain hare removal on overall tick numbers, a site adjacent to control site 1 was used for comparisons of tick burdens on the different vertebrate hosts present. However, this site received a poorer tick control regime on sheep than the treatment site, making the interpretation of the comparison impossible. Control site 2, in Inverness-shire, was used for comparisons of grouse breeding success and density with the treatment site. Several factors have been shown to be important in determining grouse breeding success and density, including climate, game-keeper density, soil quality and heather productivity (Hudson 1992, pp. 26–31), but the authors report only that the climate of the control site was similar to the treatment site. In addition, control site 2 is not an actual control, as the treatment is the reduction of louping-ill, while control site 2 has no louping-ill present at all. A true control would have had a high level of louping-ill throughout the study period, just like the treatment site before the treatment began. Controlling the analyses statistically is a suitable alternative to overcome the differences between sites that will occur inevitably in a large-scale field experiment. This is where the issue of replication becomes important. Controlling statistically for weather, tick host community, grouse food quality and quantity, etc. requires many sites rather than just the three that are reported. Laurenson et al. explain that large-scale replicated experiments on grouse-moors are logistically difficult and financially costly to run, both in terms of the manipulations themselves, and the disruption to normal moor management. We echo their concerns about the problems of replication in these types of experiment; however, where replication is not possible, proper controlling of the treatment site should be seen as essential. It is due to the combined problems of the unsuitability of controls and the lack of replication that, even before any results were obtained, Laurenson et al. were unlikely to be able to conclusively test whether a reduction in hare densities leads to a decline in tick and louping-ill virus populations. Red grouse populations are known to cycle through time with a period of between 4 and 9 years in the United Kingdom (Hudson 1992), although the mechanisms that drive the cycles (gut parasites or kinship aggression) are under dispute (Hudson et al. 2002; Mougeot et al. 2003). Laurenson et al. wanted to ‘examine the consequences of a reduction in louping-ill virus prevalence’ on breeding success and population density of red grouse. However, despite working over an 8-year period, they failed to take account of the underlying cycles in grouse abundance. Although Laurenson et al. did not set out testable hypotheses for the effect of louping-ill reduction on grouse breeding success and overall density, it is apparent from their discussion that they expected both breeding success and overall density to increase once louping-ill prevalence was reduced. Laurenson et al. showed that the difference in breeding success between the treatment site and control site 2 decreased after louping-ill seroprevalence declined to a low level (i.e. the treatment and control sites had similar levels of louping-ill, Fig. 2a in Laurenson et al.). However, no decrease in the difference between the sites in overall grouse density was found (Fig. 2b in Laurenson et al.), suggesting that louping-ill reduced red grouse breeding success, but not overall grouse numbers. This apparent paradox can be resolved easily by examining what the underlying null and alternative hypotheses should have been, in relation to the known patterns of red grouse population dynamics, rather than focusing solely on the tick–host–virus relationship. The sets of differential equations set out in Laurenson et al. and Gilbert et al. (2001) treat red grouse as a passive player, with populations of grouse pushed up or down by the level of disease present. However, we know that grouse numbers can vary cyclically, due to delayed density dependence, and therefore these dynamics should underpin any studies on the effects of louping-ill. The change in mean and median numbers of grouse from the amended Dobson & Hudson (1992) model, as louping-ill infection rate (i) increased. The distribution of grouse counts is skewed, so the median is a better estimator than the mean. The models of Dobson & Hudson (1992) are modified from Anderson & May's (1978) host–parasite model, and reproduce the observed cycles in grouse numbers over time through a delayed interaction with gut parasites. The gut parasite hypothesis has been verified experimentally (Hudson, Dobson & Newborn 1998). We use a modified version of the Dobson & Hudson (1992) model that incorporates the impacts of louping-ill on the population: dH/dt = (a − b)H − (αP + δP)P − δDH dW/dt = λP − γW − βWH dP/dt = βWH − (µP + b + αP)P − (αpP2/H)(κ + 1/κ) where H is the population size of grouse, W is the number of free-living parasite stages and P is the number of adult worms in the host. All parameters are taken from Dobson & Hudson (1992), except δD, which is the instantaneous reduction in recruitment due to louping-ill. As louping-ill affects chick survival particularly, we used δD to describe the effect of louping-ill. δD = a × i × m where a is the instantaneous birth rate of grouse, i is the infection rate of grouse chicks with louping-ill and m is the mortality rate of infected chicks; m has been shown to be around 80% in young grouse infected with louping-ill virus (Reid et al. 1978). We used this model to simulate time-series counts of red grouse under a number of levels of louping-ill prevalence (Fig. 1). An increase in louping-ill infection rate is associated with a lengthening of the grouse cycles and a narrowing of the range of grouse numbers towards the median value, which declines slightly as louping-ill infection rate increases (Fig. 2). This result matches that of Hudson & Dobson (2001): louping-ill dampens grouse cycles. Previously, it has been shown that the mean grouse numbers are reduced by the presence of louping-ill (Hudson et al. 2002), but because the distribution of grouse counts is heavily skewed, the median is the better estimator (Fig. 2). Results from the amended Dobson & Hudson (1992) model. The time series graphs show grouse numbers when (a) louping-ill is absent (i = 0%); (b) louping-ill is at moderate prevalence (i = 20%); and (c) louping-ill is at higher prevalence (i = 40%). In light of the above arguments, the mismatch between breeding success and total grouse harvests is resolved. We suggest that Laurenson et al.'s expectation of an increase in density of grouse upon removal of mountain hares appears not to be justified. Instead, we propose the testable hypothesis that a reduction in louping-ill virus would enhance the grouse population cycles, with an increase in maximum and a decrease in minimum grouse densities, and shorten the period of the cycles. This could be tested initially by characterizing the red grouse cycle length and amplitude on different moors and relating this to the level of louping-ill prevalence on each moor while controlling for other factors such as climate, keeper density and heather production. Grouse bag data are collated over a large number of moors (Hudson 1992), which should serve as a good resource this investigation. Grouse-moor management is of conservation importance, as without grouse shooting economic drivers may result in heather moors being converted to forestry or abandoned, thus losing some of their conservation interest (Thompson et al. 1995). Therefore, to maintain this important habitat, we agree with Laurenson et al. that grouse harvests must be economically viable. However, even if we accepted their methodology and results, the suggestion that louping-ill could make grouse harvests uneconomic is questionable. The model we present predicts that median numbers of grouse should be only slightly affected by louping-ill (Fig. 2), peak numbers may be reduced, but the cyclic lows may be less severe where louping-ill occurs. Hudson & Dobson (2001) suggest that grouse yields will be highest when dampening effects stop the population from oscillating, and that louping-ill can create such a dampening effect. Thus, it seems that louping-ill may not necessarily have a negative effect on grouse-moor economics as the minimum densities of grouse will be increased, and the time between nadir years will be greater (Fig. 1). While peak grouse numbers will be reduced, thus removing ‘bumper’ harvests, perhaps stability is the prudent approach to grouse-moor economics rather than cyclic boom and bust. The argument for reducing mountain hare numbers to keep grouse-moors economically viable in Morayshire has not been proven by the experiments of Laurenson et al. Before such management advice can be given with confidence, further work is required. While Laurenson et al. have put forward some evidence in support of a link between hare density, tick abundance and louping-ill seroprevalence, they fail to demonstrate a clear connection with grouse density and the viability of grouse-moors, on which they make recommendations. We have proposed an alternative relationship between louping-ill seroprevalence and grouse density from our model, and suggest that the consequences for grouse-moor economics need further investigation. We concur with Laurenson et al.'s approach using experiments to test theoretical explorations: large-scale field experimentation in animal ecology is commendable. However, experiments must be replicated and suitably controlled to rigorously manipulate the system and produce robust results and conclusions.

Recent field experiments tested the hypothesis that variations in the aggressiveness of territorial cocks drive Red Grouse (Lagopus lagopus scoticus) population cycles. The implications of these results were previously explored with parametrically flexible models that made specific assumptions about the functional form of direct density dependence and the form and timing of delayed density dependence. Although these models were characterized by apparently different stability conditions, they pointed at the same conclusion: that the occurrence of population cycles under this hypothesis relies on the strength of the interaction between density and aggressiveness around the system's equilibrium. To investigate if this important result is valid more generally, we develop a minimally specified model by lifting most of the assumptions on direct and delayed density dependence. Stability analysis of this functionally flexible model confirms that unstable dynamics are indeed more likely if small perturbations from equilibrium density have a strong impact on aggressiveness, and it unifies the stability conditions previously derived for the more specific models under a single, general condition. Further, we derive global, necessary, and sufficient conditions for instability and express them in terms of proportional changes in aggressiveness and density. For the first time since the inception of the hypothesis, the necessary condition quantifies the minimum strength of the intrinsic mechanism that would be required to cause unstable dynamics. We predict that unstable population dynamics are possible if proportional perturbations from equilibrium density are at least matched by proportional changes in aggressiveness. Existing field data indicate that the necessary condition for intrinsic cycles is satisfied in Red Grouse populations. In contrast, the sufficient condition is considerably more strict, implying that intrinsic instability is not an inevitable feature of the system. We conclude that the model is consistent with the demographic patterns of cyclic population fluctuations in Red Grouse and other birds of the grouse family.

The red grouse (Lagopus lagopus scoticus) and northern bobwhite (Colinus virginianus) are parasitized by the cecal nematode, Trichostrongylus tenuis. Our objective was to determine if T. tenuis from red grouse is infective in bobwhites. We inoculated bobwhites with infective-stage T. tenuis larvae that originated from red grouse in northern England and bobwhites in Florida. We also inoculated domestic chickens with larvae from the same sources. None of the 6 bobwhites inoculated with larvae from red grouse became infected. Five of the 6 bobwhites inoculated with larvae of bobwhite origin became infected. All of the chickens were infected. At necropsy, lesions or inflammation of the ceca were not observed either in chickens or bobwhites. The results suggest that Trichostrongylus in red grouse and northern bobwhite are distinct species. Along with absence of gene flow, differences in transmission conditions and infrapopulation levels may have resulted in differences in host specificity.

Male red grouse (Lagopus lagopus scoticus (Lath.)) contest for territory each autumn, and some males are successful while others fail to secure territories. This paper describes experiments undertaken to test whether males which were not occupying territories could become territorial if the established territory owners were removed; that is to say, whether the number of breeding males was being limited simply by the territorial accommodation available or by some deficiency in the unsuccessful birds. Previous research consisted of counts of the grouse on 100-120 ha study areas on heather (Calluna vulgaris L. (Hull)) moorland in north-east Scotland, with more detailed studies of the behaviour of individually marked birds on smaller parts of these areas (Jenkins, Watson & Miller 1963, 1967). Territorial behaviour, courtship and pair formation are described by Watson & Jenkins (1964). The population studies showed that there were many more grouse in autumn, even after the grouse shooting was over, than in the following spring. The behaviour studies showed that grouse populations from October to May consisted of (a) cocks which courted hens and defended territories, plus hens paired with them (territorial birds), and (b) non-territorial birds which did not defend territories, show courtship, pair up, or breed. Classes (a) and (b) both included birds less than 1 year old (called 'young' in this paper) and older birds. On average, 52%0 of the August population later became non-territorial over the autumn and winter and died before the next April-May (Jenkins et al. 1967), whereas both young and old territorial grouse survived the winter well and bred next summer. Consequently we postulated (Jenkins et al. 1967) that possession of territory was essential for breeding, and that territorial behaviour in autumn greatly limited the size of the next spring's breeding stock. These hypotheses were open to the criticism that although territorial behaviour was associated with the population changes, it might not really be preventing the non-territorial grouse from taking territories. The crux was to find if they would take territories and breed when vacant ground was made available. If they did not, the hypotheses would be refuted. One might then explain the presence of non-territorial birds simply by suggesting that they were immature individuals, as in many other species where some individuals do not breed till 2 years old or more.

This chapter includes a brief comparison of red grouse (Lagopus lagopus scoticus) and small mammals as study animals. I write more on how I, as a worker who has used red grouse to tackle general questions on population ecology, view the literature on dispersal in small mammals. Occasionally comparisons are drawn with red grouse and it is noted where work on small mammals has been of particular benefit. Cycles are mentioned often because several species of small mammals and grouse (Tetraonidae) are two of the notable groups of animals which show population cycles, and because advances in understanding with each group have been useful to workers on the other group.

Extant populations of Irish red grouse (Lagopus lagopus hibernicus) are both small and fragmented, and as such may have an increased risk of extinction through the effects of inbreeding depression and compromised adaptive potential. Here we used 19 microsatellite markers to assay genetic diversity across 89 georeferenced samples from putatively semi-isolated areas throughout the Republic of Ireland and we also genotyped 27 red grouse from Scotland using the same markers. The genetic variation within Ireland was low in comparison to previously published data from Britain and the sample of Scottish red grouse, and comparable to threatened European grouse populations of related species. Irish and Scottish grouse were significantly genetically differentiated (FST = 0.07, 95% CI = 0.04–0.10). There was evidence for weak population structure within Ireland with indications of four distinct genetic clusters. These correspond approximately to grouse populations inhabiting suitable habitat patches in the North West, Wicklow Mountains, Munster and Cork, respectively, although some admixture was detected. Pair-wise FST values among these populations ranged from 0.02 to 0.04 and the overall mean allelic richness was 5.5. Effective population size in the Munster area was estimated to be 62 individuals (95% CI = 33.6–248.8). Wicklow was the most variable population with an AR value of 5.4 alleles/locus. Local (Munster) neighbourhood size was estimated to 31 individuals corresponding to an average dispersal distance of 31 km. In order to manage and preserve Irish grouse we recommend that further fragmentation and destruction of habitats need to be prevented in conjunction with population management, including protection of the integrity of the existing population by refraining from augmenting it with individuals from mainland Britain to maximise population size.

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.

The number of nymphal ticks (Ixodes ricinus) on red grouse (Lagopus lagopus scoticus) chicks was inversely related to the adult birds' breeding success and population density. Some chicks less than 14 days old were found apparently blinded and dying probably due solely to very high infestations of tick larvae. In addition, tick-borne louping-ill virus, which is known to kill grouse, was probably an important cause of death of grouse chicks in this study. J. WILDL. MANAGE. 42(3):500-505 Population densities of red grouse dif- fer from area to area, depending largely upon differences in the quantity and quality of their main food, heather (Cal- luna vulgaris) (Watson and Moss 1972). However, some parts of Scotland are in- fested with numerous sheep ticks and Moore (1937) suggested that ticks kill many young grouse. This is also the opin- ion of gamekeepers, who complain that grouse are scarce on moors with many ticks. In this study we tested these sug- gestions by comparing the number of sheep ticks found on red grouse chicks with the mortality rate of the chicks and the breeding success and breeding den- sity of adult grouse. Ticks suck blood and body fluids and cause inflammation at their point of at- tachment. They also transmit louping-ill virus (Flavivirus group), which is patho- genic to red grouse (Reid 1975). Hence the ticks' role as vectors of louping ill may be more important than the harm they do by removing blood and causing inflammation. Ticks occur as larvae,

Populations of red grouse (Lagopus lagopus scoticus) undergo regular multiannual cycles in abundance. The 'kinship hypothesis' posits that such cycles are caused by changes in kin structure among territorial males producing delayed density-dependent changes in aggressiveness, which in turn influence recruitment and regulate density. The kinship hypothesis makes several specific predictions about the levels of kinship, aggressiveness and recruitment through a population cycle: (i) kin structure will build up during the increase phase of a cycle, but break down prior to peak density; (ii) kin structure influences aggressiveness, such that there will be a negative relationship between kinship and aggressiveness over the years; (iii) as aggressiveness regulates recruitment and density, there will be a negative relationship between aggressiveness in one year and both recruitment and density in the next; (iv) as kin structure influences recruitment via an affect on aggressiveness, there will be a positive relationship between kinship in one year and recruitment the next. Here we test these predictions through the course of an 8-year cycle in a natural population of red grouse in northeast Scotland, using microsatellite DNA markers to resolve changing patterns of kin structure, and supra-orbital comb height of grouse as an index of aggressiveness. Both kin structure and aggressiveness were dynamic through the course of the cycle, and changing patterns were entirely consistent with the expectations of the kinship hypothesis. Results are discussed in relation to potential drivers of population regulation and implications of dynamic kin structure for population genetics.

The lack of parameterised models showing how intrinsic factors might affect population dynamics has contributed to the belief that they are unlikely to explain population cycles. In this paper we use mathematical models to show how a social process, differential territorial behaviour between kin and non-kin, might drive red grouse (Lagopus lagopus scoticus) population cycles. We develop a simple age-structured population model which has space as a limiting resource and examine two versions of it. The first contains no kin effect and is incapable of cyclic behaviour. The second, containing a modification to reflect the effect of kinship on recruitment, shows oscillatory behaviour over most of the parameter space and produces realistic output (period, amplitude, age structure, recruitment), while its quasi-cyclic behaviour is shown to be robust under random parameter variations. Further parameterisation with field data from two study sites in north-east Scotland yields output which resembles the course of observed population cycles. The model predicts that a young cock present in autumn will have a greater probability of recruitment into the territorial population during the increase than during the decline phase of the cycle. This is consistent with field data. The model further predicts that such fluctuations in the probability of recruitment will be synchronous with fluctuations in the size of kin-clusters.

RECENT work on red grouse (Lagopus lagopus scoticus) on a moor at about 300 m altitude in Scotland1 indicates that the spring breeding stock is largely determined the previous autumn. Each year, cock grouse established a new pattern of territories in August–September, and the number and shape of these territories was maintained with only minor changes till the next breeding season in April–May. Any cocks which did not obtain territories in autumn did not breed the next summer, and mostly died before April. Thus the size of the breeding stock was annually determined through the birds' competition for territories. The chief problem was to find what controls the size of the territories.

This essay reviews studies of how red grouse (Lagopus lagopus scoticus) behave so that they space themselves out, and considers how this social behavior is related to the regulation of populations. Ecologists are becoming increasingly aware that changes in social behavior and population numbers are often associated, and that food shortage, predation, disease and bad weather are often not sufficient to give a full explanation of changes in numbers. Some workers consider that changes in food supply are needed to cause fluctuations in numbers, but others that they are not necessary. One of the difficulties is that food quality in biochemical or nutrient terms, as distinct from mere quantity of material, has been greatly neglected in ecology, despite its well-established importance for the survival, weight, physiology, reproduction and behavior of domestic animals and man. Furthermore, the different views of Andrewartha & Birch (1), Wynne-Edwards (20), Lack (6) and Chitty (3), show that theoretical views on the mechanics of population control are widely different. Anyone surveying the literature will rapidly conclude that remarkably few studies have been done on the inter-relationships between behavior, population, and food or other features in the environment. There are plenty of studies on any one of these aspects, and quite a number on population-food relations, but few on population-behavior relations, very few on food-behavior relations, and hardly any on all three aspects together.

The role of parasites in regulating populations has been the subject of debate. We tested whether parasites caused population cycles in red grouse by manipulating parasite intensities in four, paired 1 km(2) study areas during cyclic population declines over 4 years. Parasite reductions led to (1) larger grouse broods, (2) higher population densities in both autumn and spring, (3) reduced autumn population declines in one of two regions, and (4) reduced spring declines, but only in the first year. We infer that a single trophic interaction between a parasite and its host does not explain cyclic dynamics in spring breeding density in this species, although it contributed to the start of a cyclic decline. Another process was operating to drive the populations down. Together with our other results these findings emphasize that both trophic and intrinsic processes may act within populations to cause unstable dynamics.

Using different proxies of solar activity, we have studied the following features of solar cycle. (i) A linear correlation between the amplitude of cycle and its decay rate, (ii) a linear correlation between the amplitude of cycle $n$ and the decay rate of cycle $(n - 1)$ and (iii) an anti-correlation between the amplitude of cycle $n$ and the period of cycle $(n - 1)$. Features (ii) and (iii) are very useful because they provide precursors for future cycles. We have reproduced these features using a flux transport dynamo model with stochastic fluctuations in the Babcock-Leighton $\alpha$ effect and in the meridional circulation. Only when we introduce fluctuations in meridional circulation, we are able to reproduce different observed features of solar cycle. We discuss the possible reasons for these correlations.

Single Nucleotide Polymorphism in four Scandinavian populations of willow grouse (Lagopus lagopus) and two Scottish populations of red grouse (Lagopus lagopus scoticus) were assessed at 13 protein-coding loci. We found high levels of diversity, with one substitution every 55 bp as an average and a total of 76 unlinked parsimony informative SNPs. Different estimators of genetic diversity such as: number of synonymous and non-synonymous sites, average number of alleles, number and percentage of polymorphic loci, mean nucleotide diversity (pi(s), pi(a)) and gene diversity at synonymous and non-synonymous sites showed higher diversity in the northern populations compared to southern ones. Strong levels of purifying selection found in all the populations together with neutrality tests conforming to neutral expectations agree with large effective population sizes. Assignment tests reported a clear distinction between Scandinavian and Scottish grouse suggesting the existence of two different evolutionary significant units. The divergence time between willow and red grouse ranging between 12 500 and 125 000 years, in conjunction with the presence of 'specific' markers for each subspecies prompt a reassessment of the taxonomical status of the Scottish red grouse.