MAMMAL MESSAGES - LEARNING FROM THE PAST

29 1000 YEARS OF NATURAL HISTORY

Trans. Suffolk Nat. Soc. 36 (2000)

MAMMAL MESSAGES - LEARNING FROM THE PAST

PAT MORRIS

There have been many significant changes in the British mammal fauna over the past 1000 years, including the extinction of the wolf (Canis lupus), bear (Ursus arctos) and wild boar (Sus scrofa) (Yalden, 1999). Some might argue that we have much to learn from this loss among our more charismatic species. Others might justifiably point out that this country is not big enough to accommodate space-hungry large mammals as well as a burgeoning human population, preoccupied with the safety of its own offspring and livestock. Reduction in our larger carnivores was a result of interspecific competition: they lost.

Three centuries of further persecution resulted from the first Queen Elizabeth enacting legislation (‘for ye preservation of grayne’) which included provision for churchwardens to make bounty payments for every head of vermin destroyed, including hedgehogs. Under the second Queen Elizabeth, hedgehogs were given legal protection through the Wildlife and Countryside Act. Perhaps this time something had been learned.

Although these historical events and processes are interesting, perhaps the most important changes, and lessons, are to be found among the mammals of the present century. This paper outlines some significant examples.

Foremost among these is the case of the otter (Lutra lutra). This was common and widespread throughout Britain even as recently as the 1950s. Otters were shot as pests, raiding eel traps on the Thames a century ago and were still killed at the rate of hundreds per year by the otter hunts well into the 1960s. However, data from the hunts showed a sharp drop in their catch per unit effort (actually ‘finds’ per 100 days hunting) occurring after about 1957 (Chanin & Jefferies, 1978). By the 1980s otters were virtually extinct over much of central and eastern England. It would be easy to blame the hunts for this, but to do so would miss an important lesson. In fact the otter continued to decline after otter hunting ceased in 1975. The real cause of decline among the otter population was the bioaccumulation of organochlorine residues, derived from agricultural pesticides newly introduced to British agriculture. Other top carnivores were also affected, including birds of prey (Newton, 1979). Something had clearly gone wrong at the ecosystem level, the otter just happened to be one of the worst affected species and therefore the most effective indicator of trouble. Fortunately the lesson was learned: organochlorine pesticides were withdrawn from agricultural use. Many species have benefited, not just the otter, and we now have a much better understanding of the dangers posed by such substances.

However, one lesson has not perhaps been fully learned, even now. The otter is a relatively long-lived species. Pesticide residues thus have several years in which to accumulate within its tissues, causing sterility long before actual death. The result is that the otters were still around, still found by the hunts and still leaving plenty of evidence to indicate their presence, concealing the time bomb effect of accumulated poisons. But the animals were not reproducing, so that when the older generation died off, a major population


Suffolk Natural History, Vol. 36 30

collapse occurred within a relatively short time, 1957–1967. The message here is that ‘no change’ does not necessarily mean ‘no problem’.

Decline of the otter was highlighted by analysis of otter hunting records, but no similar database was available to substantiate anecdotal claims that the water vole (Arvicola terrestris) was also in decline throughout the 1970s. A review of the literature (Jefferies, Morris & Mulleneux, 1989) revealed an increase in the number of published reports for this species, suggesting exactly the opposite! However, this misleading picture resulted from increased mammal recording associated with the Mammal Society distribution surveys which were active at that time. A more subtle analysis of the words used to describe the status of the water vole, decade by decade, showed a statistically significant decline in the relative frequency of the word “common” and an increasing proportion of pessimistic words used to refer to water vole numbers. It was this study that led to the first national water vole survey, which confirmed that water voles had disappeared from nearly 70% of sites where they had formerly been recorded (Strachan & Jefferies, 1993).

Whilst the water vole’s demise has now been substantiated, lessons can only be learned if we understand why the decline has taken place. Questionnaire surveys (Jefferies, Morris & Mulleneux, 1989), population modelling (Macdonald & Strachan, 1999) and direct observations all strongly implicate the mink (Mustela vison), whose expansion has coincided with water vole decline and whose predatory habits would be likely to impact heavily on riparian vole populations. However, an important lesson to be learned, easily overlooked, is that the literature analysis showed that water vole decline has been continuous throughout this century, not just since the introduction of mink. Clearly some other factors are also involved, and focusing only on the mink may result in overlooking other issues of potentially greater significance. These might include habitat destruction, disrupted metapopulations and restriction of voles to a linear waterside fringe. Perhaps the synthetic oestrogen mimics and other endocrine disrupting chemicals now widely occurring in aquatic ecosystems are already affecting water voles? Attention is currently focused on the effect of these chemicals on invertebrates and fish, but suppose they accumulate in the storage organs of aquatic plants. What happens to cattle or water voles that might eat riparian vegetation? This is highly speculative, but shows that we should not assume that declines are caused by a single factor. Mink are probably the most serious threat to water voles, but we should not close our eyes to the possibility of other contributory causes that might in turn have a significance that goes beyond the mink/ vole issue.

But why fuss about water voles or otters? Single species conservation is out of fashion these days. In a pragmatic age it not good enough to say they are cute or that they are native species, part of our biodiversity heritage. Such arguments carry little weight with the public at large or the politicians of the day. However, it s a stark fact that water voles, and otters, live in our drinking water. If their numbers are declining fast we should take note. They are the environmental equivalent of the miner’s canary, when they stop singing a dangerous situation has been reached. We should certainly learn from this, in our own self-interest.



About a quarter of the mammals living in Britain are species that have been introduced to this country over the past 1,000 years. Whilst the naturalisation of the rabbit and various species of deer may have seemed beneficial at the time, and even for several centuries afterwards, the lesson we have now learned is that alien species can be very destructive. For example, the grey squirrel (Sciurus carolinensis) has displaced the red (S. vulgaris) almost everywhere, with Suffolk one of the last southern counties to harbour the latter. The damage done by coypu (Myocastor coypus) in East Anglia, and the subsequent costly eradication programme, are two local reminders of the threat posed by introduced species. In this case, lessons have been learned and it is illegal, under the Wildlife & Countryside Act, to release non-native mammals into the wild.

However, there is actually another mammal message here, based on further analysis of our fauna. Harris et al. (1995) published estimates for the total population size for all British mammal species. Multiplying total numbers by an estimate of average body weight, a crude figure can be calculated for the total biomass of each species. Our introduced species are both numerous as individuals and all above average size. Thus, whilst about 25% of our mammal species are introduced, they comprise more than 50% of the total mammal biomass inhabiting the British countryside. Environmental impact is proportional to biomass, numbers of species is relatively unimportant. This further emphasises the lessons about controlling alien animals, and will strike a chord with woodland managers, especially in Suffolk, trying to cope with the effects of introduced deer on our native flora.

In fact, there are more lessons to be learned from thinking about mammal biomass, rather than species or numbers. For example, whilst weasels (Mustela nivalis) and stoats (M. erminea) outnumber feral cats (Felis catus) in Britain, cats are bigger animals. Their total biomass is at least 10 times greater than that of weasels and stoats combined. It is biomass that needs to be fed every day, and a ‘biomass audit’ suggests that the impact of feral cats on prey animals will greatly exceed that of all of our native mustelids put together (excluding the badger, Meles meles).

This furthers strengthens the lesson about liberating additional species into the countryside, but it also highlights a worrying problem relating to the badger. This species has suffered extensive persecution and population declines, prompting special protective legislation to be enacted. The national badger survey in the late 1980s (Creswell et al., 1990) showed it was still a rare species in many areas, including Suffolk. However, a re-survey ten years later (Wilson, Harris & McLaren 1997) suggested that nationally there has been an increase of some 77% in total badger numbers. Many will rejoice at this, saying that the lessons of the past have been learned and that protection has been both justified and effective. I share that sentiment, but draw attention to the fact that badgers are big animals too. They are also at least partly carnivorous. Carnivores eat other animals, whose numbers must be reduced as a consequence. Badgers eat many earthworms and molluscs, also sought by the song thrush (Turdus philomelos) which showed evidence of a 40% decline in the 1980s (Marchant et al., 1990), when the badger was increasing.



Moreover, the decline averaged 12% per annum in the Southwest, double the rate elsewhere, and it is in the South-west that badgers have reached their highest densities. Correlation is not proof of causation, but nobody has yet suggested a link between these two species and perhaps another lesson is waiting to be learned?

A similar situation affects the hedgehog (Erinaceus europaeus). This too relies heavily on many of the same foods as the badger, but badgers kill hedgehogs as well. Data from the Game Conservancy (Tapper, 1992) suggests that hedgehogs have been in decline since at least the 1960s. Following studies of hedgehogs in Oxfordshire and the numbers of them killed by badgers, Micol et al. (1994) predicted the absence of hedgehogs from areas where badger density exceeds 2·27 setts per 10 km2. This implies a marked decline in hedgehog populations in certain regions of Britain, notably in the West Midlands, South-west England, South-east England and Wales. It is easier to visualise the impact of Micol’s predictions by considering actual numbers of badgers per 10 km2. If Micol and co-workers are correct, where badger numbers exceed 13 per 10 km2, hedgehogs will be in danger. That situation had already been reached in four of the ten survey regions by the 1980s (Cresswell et al., 1990), and badgers have increased by 77% since then. Respiration/ weight (Schmidt-Nielsen, 1979) and ingestion/ weight (Peters, 1983) equations, suggest that a 10 kg badger will eat about the same amount as 7 hedgehogs (weighing 600 g each), and probably more than 20 song thrushes. The same food cannot sustain them all!

There is no actual proof that falling hedgehog numbers are due to increased badger abundance. However, a substantial increase in numbers of an animal like the badger, which is both large and carnivorous, cannot be achieved without some sort of knock on effect. The message is: there is no such thing as a free lunch.

Bats have a poor public image and for a long time this obscured the many lessons they offered. People were simply not interested. If bats were declining, so much the better, they get caught in your hair don’t they? Fortunately, bats now have more friends and the public is potentially more receptive to the lessons that can be learned from these animals. However, the messages have taken a long time to sink in. For example, it was and still is, a condition of many house mortgages that the roof timbers be sprayed with suitable preservatives. Householders naturally wished to protect their single most important financial investment. What better way than to use chemicals like Lindane that were guaranteed to remain poisonous for the full 20 years of a mortgage? If a few bats, spiders and moths got sprayed as well, this was unfortunate or even a free bonus. However, Lindane treated timbers could still kill bats on contact several years after timber treatment had taken place (Racey & Swift, 1989). But bats and humans are both mammals, what kills one may surely affect the other? Yet people seemed blind to this simple message. We and our children spend eight hours of every day sleeping in the rooms directly below attics treated with chemicals that are lethal to bats, even years after application. There is certainly a clear lesson to be learned here and, belatedly, Lindane has been withdrawn from domestic use.



Surveys of bat distribution and activity have highlighted the importance of standing water to these animals. There is more bat activity near water than in other habitats. Yet bats live in trees and houses, they do not live in water! In fact, ponds and other water bodies serve as nurseries for countless insects. These develop underwater, sustained by highly productive aquatic ecosystems, emerging later to the air to breed, but also to become food for bats, birds and other animals. The lesson here is not just that rivers and ponds are important in an unexpected way and need to be kept free of pollution for example, but that bats and many other creatures depend on the integrity of the countryside as a whole. This principle is particularly well illustrated by the greater horseshoe bat (Rhinolophus ferrum-equinum), a species that has probably declined by over 90% this century. They breed in warm attics, they need cool damp caves in which to hibernate and access throughout the summer to areas that provide abundant beetles, dung flies and other suitable prey. All these requirements have to be met without travelling long distances, as bat flight is an energetically costly form of locomotion. The progressive contraction of distributional range in this species highlights an important lesson about ecosystem disruption brought about by loss of specialised habitat elements (e.g. caves, old barn roofs) and the gross ecological simplification of large scale intensive agriculture. Bats, including the greater horseshoe, also rely heavily on large bodied insects for food. The decline of these seems to be passing unnoticed and I believe there is an important message here as well, but that is another story.

We should appreciate bats more. The changes they show over recent decades reflect many useful lessons from the past. Ecosystem integrity is one such, now being slowly adopted as the principle of conservation in “the Wider Countryside”. There are many species, not just mammals, which will never be adequately supported just by setting aside nature reserves. They require a mosaic of features, widely distributed, and need to live and feed in the landscape at large. I think this lesson is being learned and is an increasingly important part of countryside management policy. It may become still more relevant in the future as we begin to re-evaluate what we think the countryside is actually for, now that conventional farming is becoming increasingly non-viable as the main land use option in many areas.

The dangers posed by habitat fragmentation are another useful mammal message from the past, highlighted by the dormouse (Muscardinus avellanarius). Surveys of good dormouse habitat in Herefordshire showed that woods close together or linked by hedges were more likely to contain dormice. Moreover, woodlands exceeding 20 ha in area frequently still harboured this species, but isolated woods smaller than this had a sharply decreased incidence of dormice (Bright, Mitchell & Morris, 1994). Clearly woods need to be of substantial size to maintain secure viable populations in the long term. Yet the inventory of remaining ancient semi natural woodland (the best habitat for Muscardinus), shows most of the remaining habitat of this type is in patches less than 20 ha in size, too small to sustain viable populations of dormice in the long term. (Spencer & Kirby, 1992). Woodland fragmentation is one of the key changes over past centuries that has contributed to the decline of the



dormouse and many Midland counties now have very few dormouse localities remaining as their woodland habitat has been severely reduced in area and is now broken up into many small parts (Bright & Morris, 1996). This is particularly obvious in Warwickshire, where only one locality remained (increased to two in 1998, by a reintroduction near Coventry).

The dormouse also offers a lesson in Kent, where part of the A21 still has them in its adjacent hedgerows and the trees meet overhead allowing arboreal access to the land on either side. The attention of planners and landscape architects, quite rightly, turned to the likely impact of road widening on the dormouse. However, the focus was on the narrow issue of which woods or hedgerows would be destroyed, affecting a few dozen dormice, depending upon which route was selected for the widened road. But the real lesson to be learned is that dormice (in common with many small mammals, reptiles, spiders and countless other invertebrates) are very reluctant to cross wide areas of open ground, such as a road. Widening the A21 will result in a swathe of open verges and road surface, nearly 100 m wide in places, traversing Kent from London to Hastings. The effect of this as a barrier to free movement of animals 100 km long, is unknown but certain to be of far greater significance than the issue of whether this wood or that is destroyed in the process. The dormouse offers a message: we need ‘habitat bridges’. This lesson is of very wide application, but there are few signs of its being heeded, at least in this country.

Nor do we know much about the relative willingness of animals to cross different widths and types of road. For example, hedgehogs are frequent casualties on ordinary roads and dual carriageway trunk roads, but they are seldom seen dead on motorways. Yet badgers and foxes (Vulpes vulpes) are frequent motorway casualties. There is probably an important message here too, but it is receiving little attention.

There have been interesting changes in attitudes towards mammals over the years (Morris, 1987), offering implicit messages. For example, an opinion survey carried out by the magazine BBC Wildlife in 1991 showed that the two most popular British mammals (otter and badger) were species that had never been seen by most of the British population. Apparently, people like their mammals, whether they have personal experience of them or not. Urban people (the majority) may therefore drive policies and democratically elected governments, based on feelings and sentiment as much as direct experience. The lesson of this is now being learned, perhaps too late, by those wishing to prevent the abolition of hunting with hounds. (the fox was the third most popular animal in the survey cited above…….).

Looking to the future identifies further messages. One of these concerns farming, particularly using grazing mammals. Traditional breeds of cattle cannot grow to marketable size within the 30 month time limit set by BSE control measures, yet these are often the best breeds for use on “marginal” habitats, where biodiversity is greatest. Moreover, extensive grazing systems are no longer economically viable, especially in the cooler uplands where grass grows slowly and for only a small part of the year. While we focus on the social and economic implications of this unfolding crisis, we risk



overlooking another mammal lesson. Returning to the biomass perspective on relative abundance of mammals, we find that fewer than five species of domestic mammals account for 95% of the total tonnage of mammals impacting on the British countryside. Most of these are cattle and sheep. If substantial numbers of these are withdrawn, especially from upland areas, because nobody can afford to keep them there any more, what will the future landscape of Britain be? If today’s open grassy moors and hillsides are no longer grazed, substitution by scrub and stunted woodland is likely. Do we want this? What effect will it have on birds, plants and insects of open areas, especially in the uplands? Here is a mammal message that needs requires serious attention!

A final message for the future can be illustrated again by the hedgehog. Game Conservancy data (Tapper, 1992), suggest that hedgehogs have been steadily declining for at least 40 years. We enter the 21st century with evidence that one of our most familiar and popular animals may be rapidly disappearing, but we do not properly understand what is happening. We do not know whether the decline might be 5% per year or double that. We do not know even whether the decline is real or an illusion brought about by the nature of the Game Conservancy’s data (numbers killed by gamekeepers each year), yet this is the best data source we have. What is true of the hedgehog is true of other mammals too, we have no way of assessing their fortunes because there is no national mammal monitoring system to keep track of what is going on. It is good news that many counties now have mammal mapping programmes in place, including Suffolk, but the ornithologists reached this stage with a reliable national bird atlas over 20 years ago (Sharrock, 1976). Nowadays, extensive monitoring (i.e. counting) schemes supplement distributional information to provide very detailed annual appraisals of “The State of the Birds”. There is still nothing like that for mammals. Changes in the British mammal fauna will continue, but many consequential messages will fall on deaf ears, because we are not listening.

References

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Bright, P. W. & Morris, P. A. (1996). Why are Dormice rare? A case study in conservation biology. Mammal review 26: 157–187.

Chanin, P. R. F. & Jefferies, D. J. (1978). The decline of the otter (Lutra lutra) L. in Britain: an analysis of hunting records and discussion of causes. Biological journal of the Linnean Society 10: 305–328.

Cresswell, P., Harris, S. & Jefferies, D. J. (1990). The history, distribution, status and habitat requirements of the Badger in Britain. N.C.C., Peterborough.

Harris, S., Morris, P., Wray, S. & Yalden, D. (1995). A review of British mammals. J.N.C.C., Peterborough.

Jefferies, D. J., Morris, P. A. & Mulleneux, J. E. (1989). An enquiry into the changing status of the water vole Arvicola terrestris in Britain. Mammal review 19: 111–131.



Macdonald, D. & Strachan, R. (1999). The mink and the water vole- analyses for conservation. Wildlife Conservation Research Unit, Oxford.

Marchant, J. H., et al. (1990). Population trends in British breeding birds. B.T.O., Tring.

Micol, T., Doncaster, C. P. & Mackinlay, L. A. (1994). Correlates of local variation in the abundance of hedgehogs Erinaceus europaeus. Journal of animal ecology 63: 851– 860.

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University Press, Cambridge. Racey, P. A. & Swift, S. M. (1986). The residual effects of timber treatments

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England and Wales. Biological conservation 62: 77–93. Strachan, R. & Jefferies, D. J. (1993). The water vole Arvicola terrestris in

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population, 1988–1997). Peoples Trust for Endangered Species, London Yalden, D. W. (1999). The history of British mammals. Poyser, London

P. A. Morris School of Biological Sciences Royal Holloway College (University of London) Egham Surrey TW20 OEX

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