T H E STATUS OF T H E BADGER (MELES MELES) IN BRITAIN, WITH PARTICULAR REFERENCE TO EAST ANGLIA
STEPHEN HARRIS Summary A survey in the 1980s showed that there are about 42,000 badger social groups in mainland Britain. Long-term capture-mark-recapture and postmortem data were used to estimate the recruitment and annual mortality rates for the British badger population; these were found to be roughly in balance. However, the effects of current landscape changes on the rate of sett losses are unknown for most parts of Britain. The exception is Essex, where 36% of all known setts were destroyed in the 20 years up to the mid-1980s, mainly due to agricultural improvements. The data from the national survey were also used to calculate past changes in badger populations. Last Century about 1450 badger social groups were exterminated in Norfolk and Suffolk by gamekeepers, and the current low numbers in these two counties (approximately 150 social groups) are due to past persecution and not an absence of suitable habitats. For Britain as a whole, the badger population could be 39% higher if simple measures were taken to increase habitat diversity. It is suggested that reintroductions are a potentially valuable means of helping rebuild the badger population in Norfolk and Suffolk. Introduction Monitoring population changes for most species of mammal is very difficult, except on a local scale, and there are few reliable national population estimates. The exceptions are species such as grey (Halichoerus grypus) and common (Phoca vitulina) seals, which can be counted from aerial photographs (Summers, 1979; Harwood & Hiby, 1984), and some of the rarer species of bat, such as the greater horseshoe (Rhinolophus ferrumequinum) (Ransome, 1991). For nocturnal elusive species such as the badger (Meies meles), it is particularly difficult to obtain reliable estimates of numbers, and until recently there was no information on the size of the British badger population, any past population changes and current population trends, or any measure of the potential impact of persecution or land-use changes on badger numbers. In this paper, I describe a method of measuring the size of the British badger population, and show how these data were used to quantify the population pressures facing badgers in Britain. Calculating the number of badger social groups in Britain There have been two national badger surveys in Britain. The first was instigated by the Mammal Society in 1963 with the aim of recording the numbers and distribution of badger setts on a county by county basis, using volunteer recorders. This was a very successful exercise; over 4300 setts were
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included in the initial report (Neal, 1972), and 14,030 setts in the final analysis (Clements, Neal & Yalden, 1988). With time, however, it became apparent that there were two main limitations to this survey. First, in recent years it has been found that each badger social group has a number of different types of sett within its territory (Cresswell, Harris & Jefferies, 1990). O f t h e s e , the main sett isof particular importance, beingincontinuous use and the principle breeding sett (Cresswell et al., 1992). However, the Mammal Society's survey did not distinguish these different types of sett, and this led to difficulties when interpreting the results. Second, the survey was conducted over a protracted period, approximately 25 years. DĂźring this time there were great changes in the legal protection given to badgers (Skinner, Jefferies & Harris, 1989) and also their status in at least some parts of Britain (Skinner, Skinner & Harris, 1991), thereby adding to the difficulty of evaluating the results of the survey. Because of these problems, the Nature Conservancy Council initiated a second national badger survey. This was undertaken between November 1985 and February 1988; 2455 one-kilometre squares were surveyed for badger setts and signs of badger activity. Each sett that was found was classified to one of four types: main, annexe, subsidiary or outlier, depending on its size, location in relation to other setts, and its level of activity. Identifying main setts was particularly important, since each badger social group normally has one main sett. In addition, a habitat map was prepared for each of the one-kilometre squares surveyed. These data were used to estimate the number of badger social groups in Britain. T o d o this, each of the squares surveyed had been allocated to one of 32 land classes using a scheme devised by the Institute of Terrestrial Ecology (Bunce, Barr & Whittaker, 1981a; 1981b). For each o f t h e s e land classes, the mean badger density was calculated as the number of main setts (and hence badger social groups) per Square kilometre; since the area of each land class in Britain was known, the total badger population could then be calculated. This was estimated to be about 42,000 social groups (Reason, Harris & Cresswell, 1993). Estimating badger mortality rates In order to calculate how many actual badgers there are in Britain, data from capture-mark-recapture studies were used to estimate the mean group size for badgers. From several studies, this was shown to be six adults i.e. there are approximately 250,000 adult badgers in Britain (Cresswell, Harris & Jefferies, 1990). Mortality rates are higher for male badgers than females, with annual mortality rates of about 30% for males, 20% for females. This results in the adult sex ratio being biased towards females (1:1.3) (Harris & Cresswell, 1987). H e n c e the adult badger population in Britain is about 109,000 males and 141,000 females, with an approximate adult annual mortality of 33,000 males and 28,000 females i.e. 61,000 animals (Harris et al., 1992). Calculating cub production was more difficult. T o do this, data were collected f r o m 352 adult female badger carcasses collected in south-west
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Suffolk Natural History, Vol. 29 Britain between March 1988 and March 1990. Post-mortem analysis showe that each year 45% of adult females had either fresh placental scars or foetuses (i.e. they had implanted embryos), and so approximately 63,500 females produce cubs each year. Since mean litter size is 2.7 (Anderson Trewhella, 1985), annual cub production is about 172,000 animals. To calculate the rate of cub mortality, data from two long-term capture-mark recapture studies were used (Cheeseman et al., 1987; Harris & Cressw 1987). These were based in Gloucestershire and the city of Bristol respe tively, and showed that 61.5% of cubs died in theirfirstyear. Of these,37.5% died underground prior to the age at which they would have emerged abo ground, mainly as a result of infanticide by other sows (Cresswell et al., 1992), and 24.0% died post-emergence. Hence, nationally about 64,500cub die pre-emergence in the first few weeks of life, 41,500 post-emergence, an approximately 66,000 cubs survive theirfirstyear. Thus cub recruitment is approximately equal to the annual rate of adult mortality (Harris et al., 1992). Whilst these are obviously broad-based calculations, they do show that despite high mortality rates, cub recruitment approximately equals adult mortality. The most important cause of mortality is probably road deaths these accounted for Over 50% of all known badger deaths in the two lon term studies in Gloucestershire (Cheeseman, Wilesmith & Stuart, 1989) an Bristol (S. Harris & W. Cresswell, unpublished data). Yet there is no evidence that even such high levels of road mortality are having an impact badger populations nationally, although locally there may be significant effects. This is in contrast to the Netherlands, where road traffic accidents a thought to have been the major factor leading to a substantial population decline since the 1960s (Wiertz & Vink, 1986; van der Zee et al., 1992 Whilst mortality factors acting on individual badgers seem broadly to be balance with recruitment rates, there are a number of limitations with th data on which these calculations were based. In particular, they are deriv from studies of populations living at high densities in south-west Britain. How typical these data are of badgers living at lower densities, notably East Anglia and northern Britain, is at present unknown. However, Cresswell, Harris & Jefferies (1990) showed that only 9.8% of the Britis badger population lived at very low densities (i.e. below 0.1 social groups p Square kilometre), and so the data used in these analyses are probably typ of the greater part of the British badger population.
How threatened are badger setts in Britain? The other factor to consider when trying to understand whether the Britis badger population is stable is the rate of sett losses. Whilst the mortality rat acting on individual animals seem to be balanced in broad terms by recr ment, the rate of sett losses (and hence potentially the loss of entire soc groups) has not yet been quantified for most of Britain. The one exception Essex, for which there was an extensive data base collected by Cowlin (197 who documented 548 setts between 1963 and 1971. These setts were al surveyed between 1983 and 1986, so that there was approximately 20 ye Trans. Suffolk Nat. Soc. 29 (1993)
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between the two surveys. On the resurvey, Skinner, Skinner & Harris (1991) found that, of the original 548 setts, 200 (36%) had become derelict or had disappeared. Of the remaining setts, the proportion thought to contain badgers had declined from 54% to 40%, and the modal sett size was reduced from six holes to three. Most of the setts that had been lost had gone due to land use changes, and the authors argued that most of these had probably been destroyed during agricultural improvements. Finally, sett losses were probably continuing, with nearly a quarter of the remaining setts affected by direct disturbance. This decline had occurred in a county with a rather low initial badger density. The net result was to fragment the remaining badger population, and in the long-term this might affect the viability of isolated groups of setts (Skinner, Skinner & Harris, 1991). Population fragmentation is likely to be particularly serious in areas with few linear habitat features, since work in the Netherlands has demonstrated the importance of hedgerows and other features in providing corridors for dispersing animals, thereby promoting movement between isolated groups of badgers (Broekhuizen elal., 1986; Lankester et al., 1991). The work in Essex clearly demonstrates how vulnerable badger populations can be, but it is difficult to know how typical this Situation is of the rest of Britain. Being on the edge of London, Essex is likely to represent an extreme case. Between the two surveys it was subjected to considerable pressures from an increasing human population, farming intensification and habitat changes such as woodland losses, new road schemes, including the construction of two motorways, and the development of London's third airport at Stansted. T o see if a similar pattern of changes is occurring elsewhere in Britain, a number of local badger groups are currently organising similar repeat surveys, and we should shortly have a better picture of the rate of sett losses in Britain as a whole. The effects of persecution on badger numbers Whilst it is not yet possible to be sure whether Overall the British badger population is stable, increasing or declining, it is possible to estimate the likely past population changes. Cresswell, Harris & Jefferies (1990) described these changes; at the Start of the Century the population was lower than at present, as a result of pressure from gamekeepers, but badgers were probably not as rare as many observers at the time believed. Since then badger numbers have increased, and local surveys from 1960 onwards generally reported healthy badger populations, although a number of recorders expressed concern at the levels of persecution, particularly by badger diggers. To quantify the impact of past persecution on badger numbers, Reason, Harris & Cresswell (1993) used the data from the national badger survey. They identified those counties where digging was, or had been, extensive. There were eleven such counties: Cheshire, Clwyd, Derbyshire, Mid, South and West Glamorgan, Gwent, Norfolk, Suffolk, and South and West Yorkshire. Excluding the data from these counties, and re-calculating the number of badgers in Britain, suggested that 1543 badger social groups had
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been lost as a result of persecution i.e. nationally the badger population should be about 3.7% higher. However, virtually all this loss (1450 badger social groups) had occurred in Norfolk and Suffolk, and elsewhere in Britain badger losses due to persecution had been minimal. Most of the losses in Norfolk and Suffolk occurred last Century; early records showed that in the 1800s badgers had been common in some parts of Norfolk (Southwell, 1901; Patterson, 1908) and parts of Suffolk (Rope, 1911). However, up to the First World War, gamekeeper numbers in Britain had been very high, with over 23,000 nationally (Tapper, 1992). One gamekeeper can effectively manage about four Square kilometres of land, and this would be the density of keepers on a well-managed estate. In Norfolk in 1911 there was virtually this density of gamekeepers across the whole county, and the Situation in Suffolk was similar (Tapper, 1992). Thus Norfolk and Suffolk were very extensively keepered, and this pressure led to drastic declines of a variety of species such as buzzards (Buteo buteo) (Moore, 1957), as well as badgers. Hence whilst the habitat in East Anglia is not ideal for badgers, it certainly is not as bad as the current low population might suggest, and badger numbers should be significantly higher. The loss of about 1450 social groups of badgers occurred approximately a Century ago, and it may seem strĂ¤nge that in the interim period badger numbers in Norfolk and Suffolk have not recovered. However, long term studies in Gloucestershire have shown that even in high density areas, badgers are poor colonists (Cheeseman et al., 1993), and in East Anglia there were so few badgers left that the population was fragmented and the chances of recolonisation reduced. The scattered and low number of occupied setts in East Anglia is summarised in recent local surveys. In Cambridgeshire, badger setts are mainly found west of Cambridge and in the south-eastern corner of the county (Vine, 1965); in Norfolk only 23 setts were occupied in 1971 (Vine, 1970), and in the next decade the number of occupied setts fluctuated between 25 and 35 (Anon., 1981). In fact, in most of west Norfolk badgers would have become extinct if it was not for reintroductions in the 1970s. More recently there has been a small improvement in the Situation in Norfolk, with 50 to 60 setts occupied by 1992, with signs of new areas being colonised (A. E. Vine, pers. comm.). In Suffolk records are scattered (Cranbrook, 1953). At present approximately 270 setts have been recorded, of which 88 are thought to be main setts. The distribution is patchy, and almost entirely in the south of the county (M. Grimwade,/?er.s. comm.). Thus in Norfolk and Suffolk there are still only about 150 known social groups of badgers, approximately 1300 fewer than the habitat can sustain.
The effects of land use changes on badger numbers It is perhaps anomalous that land use changes, and particularly those associated with increasing agricultural intensification, are a significant cause of recent sett losses in at least some areas (Skinner, Skinner & Harris, 1991), since the current high numbers of badgers in Britain are a direct consequence of our pattern of land use, and particularly of our pattern of agriculture. In fact 97% of the badger social groups in Britain are found in managed i.e.
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agricultural, landscapes. This dependence on agriculture landscapes is a consequence of the feeding behaviour of badgers; they are omnivores, and in most lowland areas they feed primarily on large numbers of the earthworm Lumbricus terrestris. These are most readily available to badgers in short grassland and deciduous woodlands (Kruuk, 1978; Kruuk et al., 1979), and the availability of habitats in which to forage for earthworms is important in determining badger home rĂ¤nge size and configuration (Kruuk & Parish, 1982). In addition, when pasture is replaced by cereals. this leads to reduced food availability for the badgers, and hence a decline in body weight (Kruuk & Parish, 1985). To examine the effects of the patterns of land use on badger numbers, Reason, Harris & Cresswell (1993) used the data from the national badger survey. They showed that nationally badgers selected areas with hedgerows, treelines, semi-natural broadleaved woodlands, semi-natural mixed woodlands, mixed plantations, parkland, tall scrub, low scrub, bracken, running natural water, lowland unimproved grassland, semi-improved grassland and improved grassland. Some of these features e.g. scrub and woodlands, were selected as sett sites, whereas others such as grasslands were important for foraging for earthworms. In the agriculturally managed landscapes of Britain, Reason, Harris & Cresswell (1993) showed that one-kilometre squares with five or more of those habitat features selected by badgers (with the proviso that where the three grassland types were all present, they only counted as two habitat features, not three) had a significantly greater badger density than those with four or less. Clearly, whilst badgers are closely associated with agricultural landscapes, they are also dependent on landscapes that have a certain minimum amount of diversity, and numbers decline in areas with excessive management. The decline of badgers in Essex with increasing levels of landscape change (Skinner, Skinner & Harris, 1991) supports this argument. Reason, Harris & Cresswell (1993) found that only 42.4% of the onekilometre squares in the managed landscapes had at least five of the habitat features favoured by badgers, and if the remaining 57.6% were improved to have at least five of the preferred habitat features (and the effects of past persecution were removed), the British badger population could be 39% higher, at just over 58,000 social groups. These calculations do not stipulate a minimum area for any of these landscape features, simply that they are present in a one-kilometre Square. Thus for very small improvements in our landscape diversity, there could be a very substantial increase in badger numbers. Care should be taken when interpreting these calculations on the impact of landscape changes on badger numbers. At the turn of the Century badger numbers were much lower, and they are thought to have built up following the First World War. The exact time-scale or magnitude of the population increase is unknown, and so whether landscape changes had most effect in reducing the potential for increase, or directly causing the loss of badger social groups, is unknown. However, it is likely that both types of loss occurred, although the relative importance of each cannot be estimated.
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Conclusions Simple calculations based on the data from the national badger survey can help understand the past history of badgers in Britain, why they are currently so rare in areas like East Anglia, what factors have caused that rarity, and what habitat improvements are likely to benefit British badger populations. Now this information is available, sensible measures can be taken to help reestablish the East Anglian badger populations. New legislation has meant that the threat of widespread persecution has gone (although locally this can still be a problem), yet the badger population is only likely to re-establish itself slowly if left unaided. Reintroductions in west Norfolk in the 1970s were successful (Anon., 1981), and a series of reintroductions in Suffolk have shown signs that they may be a promising way to help rebuild local badger populations (M. Grimwade, pers. comm.). Further reintroductions, with careful monitoring of their success, seem to be a potentially valuable management technique in areas such as Norfolk and Suffolk.
Acknowledgements The data that formed the basis of this paper were collected and analysed during studies funded by the Natural Environment Research Council, the Nature Conservancy Council and the Vincent Wildlife Trust. These bodies are gratefully acknowledged. In addition, a number of people worked with me on these projects, and I am most grateful to Chris Cheeseman, Penny Cresswell, Warren Cresswell, Don Jefferies, Pete Mallinson, Paola Reason, Chris Skinner and Paul Skinner for their very considerable input. Finally, I would like to thank Margaret Grimwade and Tony Vine for keeping me upto-date with the status of badgers in East Anglia, and Kathy Claydon for commenting on a draft of the manuscript.
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