A History of British Mammals

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by Derek W. Yalden

(also see Derek's lecture notes on the history of British fauna and for species-specific issues in Britain)

 

How many mammals are there in Britain?

This deceptively simple question is in fact a very ambiguous one, and the answers are both difficult to provide and yet very interesting in their uncertainty. To start with the ambiguity: “how many species”, or “how many individuals”?

“How many species” ought to be easily decided, but it isn’t. “How many individuals” is a nonsense question, since the answer changes by the minute. Yet we all know that some mammals are rare and others common. If we can state that much, we must have some idea of their numbers. The attempt to provide those numbers is a very interesting investigation of the state of our fauna, and the changes we have inflicted on it over 5,000 years.

 

How many species?

We ought at least to know how many species of mammal we have in Great Britain. One answer is about 60 terrestrial species, including 15 rodents, 14 bats, 11 carnivores, 10 artiodactyls, 6 insectivores, 3 lagomorphs and a marsupial. Even that answer is uncertain, because we now know that the population of what has always been considered the commonest bat, the Pipistrelle, actually includes two very similar species. Moreover, another 4 or 5 species of bat have been recorded here on a few occasions, either as natural vagrants blown off-course during migration or as stowaways on boats.

Do we include them, as the bird watchers do for their rare migrants, or restrict ourselves to breeding species?

 

Marine mammals

Another uncertainty concerns marine mammals. The two breeding seals, Common and Grey, should surely be added to the 60; they really do breed on British soil. However, there are another 4 species of arctic seals, including the Walrus, that turn up occasionally.

There are also all the whales and dolphins. Some of these, the Bottle-nosed Dolphin and Porpoise, for example, are closely tied to coastal waters, and perhaps deserve to be regarded as British mammals, but there are a number of other species that are less closely tied to coasts, ranging through to deep oceanic species, like the beaked whales, that only turn up very infrequently. There is no obvious line of division.

 

Then and Now

The same lack of a dividing line applies to time: we have about 60 terrestrial mammals living in Britain now. Only twenty years ago, we had another two, the Mouse-eared Bat which became extinct “naturally” and the Coypu which was deliberately exterminated as a pest.

About 300 years ago, the Wolf died out, and in the previous century the Gray Whale did. Earlier still, the Brown Bear, Elk, Beaver, Aurochs, Wild Boar and Lynx also occurred naturally in Britain until, variously, the Bronze Age, Roman or later times (Table 1), but were exterminated by some combination of habitat change (caused by farming) and hunting (either to eliminate pests or to exploit fur, meat and other attributes). Should they be added to the list of British mammals?

 

Table 1. Mammals that have become extinct in Britain over the last 15000 years, together with the likely date of extinction and cause.

Common nameSpeciesDateCause
Mammoth Mammuthus primigenius 12500 b.p. Climate
Saiga antelope Saiga tatarica 12400 b.p. Climate
Arctic fox Alopex lagopus 12400 b.p. Climate
Lemming Lemmus lemmus 10500 b.p. Climate
Arctic lemming Dicrostonyx torquatus 10500 b.p. Climate
Narrow-headed vole Microtus gregalis 10500 b.p. Climate
Pika Ochotona pusilla
10000 b.p. Climate
Wild horse Equus ferus 9330 b.p. Climate
Giant elk Megaloceros giganteus 9225 b.p. Climate
Reindeer Rangifer tarandus 8300 b.p. Climate
Wolverine Gulo gulo 8000 b.p. Hunting
Northern vole Microtus oeconomus 3500 b.p. Climate
Elk Alces alces 3400 b.p. Hunting
Aurochs Bos primigenius 3250 b.p. Hunting
Lynx Lynx lynx 500 A.D. Hunting
Brown bear Ursus arctos 500 A.D. Hunting
Beaver Castor fiber 1300 A.D. Hunting
Wild boar Sus scrofa 1500 A.D. Hunting
Wolf Canis lupus 1700 A.D. Hunting
Muskrat Ondatra zibethicus 1935 A.D. Hunting
Coypu Myocastor coypus 1987 A.D. Hunting

Introductions

Over the period that native species have been lost, a number of foreign species have been imported - sheep, goats and domestic cattle, probably domestic pigs as well, in the first wave about 5500 years ago, but since then horse, House Mouse, Black Rat, Fallow Deer, Rabbit, Brown Rat, Grey Squirrel, three more deer (Sika, Chinese Muntjac, Chinese Water Deer) and the Red necked Wallaby (Table 2). As non-native species, should we take these off the list of British mammals? They certainly could not have got here naturally.

 

Table 2. The mammals introduced to Britain in the last 15,000 years. Uncertainties are highlighted by a '?'. The domestic species could have been domesticated in Britain from their wild ancestors, but almost certainly were not. The case for the Harvest Mouse and Brown Hare being introduced is circumstantial. Dates for 20th Century addditions to the fauna are dates of escape/establishment, not original importation.

Common nameSpeciesDateReason
Dog Canis familiaris 9000 b.p. Companion animal
Sheep Ovis aries 5400 b.p. Food
Goat Capra hircus 5400 b.p. Food
Ox Bos taurus 5400 b.p. Food
Pig Sus scrofa 5400 b.p. Food
Orkney Vole Microtus arvalis 5400 b.p Accident
Horse Equus caballus 4000 b.p Transportation
Scilly Shrew Crocidura suaveolens 4000 b.p. Accident
House Mouse Mus domesticus 3500 b.p. Accident
Cat Felis catus 2500 b.p. Pest control
Brown Hare Lepus europaeus 2500 b.p. Food or Cult
Black Rat Rattus rattus 200 A.D. Accident
Fallow Deer Dama dama 1100 A.D. Food
Rabbit Oryctolagus cuniculus 1150 A.D Food
Brown Rat Rattus norvegicus 1728 A.D. Accident
Sika Cervus nippon 1860 A.D. Amenity
Grey Squirrel Sciurus carolinensis 1876 A.D Amenity
Edible Dormouse Glis glis 1902 A.D. Ame
Chinese Muntjac Muntiacus reevesi 1922 A.D. Amenity
Muskrat Ondatra zibethicus 1927 A.D. Fur
Red-necked Wallaby Macropus rufogriseus 1940 A.D. Amenity
Coypu Myocastor coypus 1944 A.D. Fur
Chinese Water Deer Hydropotes inermis 1945 A.D. Amenity
American Mink Neovison vison 1958 A.D. Fur

Much depends, of course, on why we want to know the number of mammals in Britain in the first place. If we are interested in the natural fauna of these islands, the terrestrial native species are the important ones. If, conversely, we want to know about the impact of mammals in the present day on farming, and forestry, or indeed on the other animals in our ecosystems, then a full list of all the species now here is critical. We would not have so many Buzzards if we did not have so many Rabbits, and farmers would not be so concerned about crop-damage.


How many individuals?

So what about the other question, how many individuals? The concern about rabbits is at least partly a concern about how numerous they are. The same considerations apply to deer and forestry, to seals and fisheries, to Badgers and bovine tuberculosis: the species are of real commercial concern because they appear to be numerous, perhaps increasing, and are therefore very noticeable and perceived to be causing damage.

At the other end of the scale, rare species like the bats, the Dormouse, Pine marten and Otter cause concern because they are rare, or because they have been rare and are slowly recovering. Yet others, while still widespread, are becoming rarer; Brown Hares seem to be much less frequent on farmland, Water voles are scarcer along waterways, and Red Squirrels are still retreating as Grey Squirrels spread.

All these questions involve at least some idea of numbers, but until very recently the numbers of only a few of our wild mammals had been estimated. The seals, or at least the mothers with pups, have been counted by aerial photography during their breeding seasons, and some of the bats (notably the horseshoe bats) have been counted in hibernation and in their breeding colonies, but most mammals remain rather uncertainly known.

 

When do we count?

By restricting the attempt to a “spring” pre breeding season, we overcome the problem of rapidly changing numbers as new young are born, and by comparing abundances of different species with each other, an attempt has been recently made to provide an overall estimate of just how many wild mammals we have.

The answer is possibly about 285 million, we think; mostly small mammals, particularly Common Shrews, Bank Voles, Wood Mice and Field Voles. Only the Field Vole, with about 75 million in spring, is likely to be more numerous than people in Britain (about 65 million, or ~48 million adults for fairer comparison with just the breeding populations of other mammals).

Such figures are, of course, very imprecise but they do provide an extra level of understanding that we did not have previously. For instance, they establish just how rare the bats are, compared with other small mammals; even our commonest bat the pipistrelle, if it is only one species, numbers no more than 2 million, clearly much rarer than the Common Shrew (42 million), Wood Mouse (38 million) and Field Vole. The aquatic mammals, Otter, Water Shrew and Water Vole are also much scarcer than terrestrial species of comparable size because they are limited to a restricted habitat.

 

Size matters

There is also the relationship between size and abundance: large mammals are, on average, rarer than small ones. At the extremes, there are about 75 million Field Voles but only 360,000 Red Deer.

This apparent relative scarcity of larger mammals tends to contradict our perceptions of them as pests of agriculture and forestry. Perhaps a better understanding of the importance of the larger mammals is gained if we convert their numbers to biomass - that is, we multiply the numbers by average masses.

The biomass of wild mammals in the countryside is very much dominated by two groups of animals that do seem to have a major impact, the lagomorphs - hares and rabbits - and deer. Since it is their masses as much as their numbers that have to be supported by the vegetation that they eat, their impact on the rural economy is indeed considerable.

What about us?

However, this extrapolation leads us onto another significant feature of mammals in the British countryside - domesticated and farmed mammals. If there are about 285 million wild mammals in Britain, there are also about 21 million breeding sheep, 4 million cattle, 0.8 million pigs, 0.75 million horses and of course 48 million adult humans even before we consider other pets, such as dogs cats, rats, rabbits and rodents, not out in the countryside. All these are large mammals, and their biomasses are considerable. To put them in context, the biomass of all the wild mammals amounts to about 2% of the total, while the domestic ungulates contribute 56% and humans 42%.

Also, the biomass of wild mammals in the countryside is only two-thirds what is was when Britain was covered in woodland 6,000 years ago and Elk, Wild Boar and Aurochs accompanied Roe and Red Deer. However, the biomass of mammals today is still 33 times greater than it was then; a measure of how enormously we have changed the ecology of the countryside. Grasslands, with or without fertilizer, produce much more growth each year than woodlands, so can support more grazing animals, and in turn they and our other crops support us. There is no longer room in Britain for large numbers of large wild animals, and when the larger ones do become too common, we tend to notice them as pests.

 

Further reading

Yalden, D. W. (2003) Mammals in Britain - A HIstorical Perspective. British Wildlife, Vol 14(4), pp 243-251

Yalden, D. W. (1999) The History of British Mammals. Poyser, London

Derek Yalden's online Lecture Notes on British Mammals at the University of Manchester - links will open in a new window:

 

- Lecture 1: Origins of British Mammal Fauna

- Lecture 2: Extinctions and Introductions

- Lecture 3: The Balance of the Fauna

- Lecture 4: How Many Mammals

- Lecture 5: Shrew Ecology - Metabolic Limitations to Small Size

- Lecture 6: Hedgehogs - Suburban Guests and Rural Pests

- Lecture 7: Ecology of Bats - Life on a Physiological Knife-edge

- Lecture 8: Pesticides, Perception and Protection Problems for Bats

- Lecture 9: Badger Ecology and Conservation

- Lecture 10: Bovine Tuberculosis in Cattle and Badgers

- Lecture 11: Red Foxes as Pests - Sheep and Game Birds

- Lecture 12: Foxes and Rabies Control

- Lecture 13: Stoats and Weasels - Species Packing and Variation

- Lecture 14: Otter Protection and Conservation

- Lecture 15: Red and Grey Squirrel Ecology: Competitors or Vicariants

- Lecture 16: Squirrels versus Forestry

- Lecture 17: Coypu and Muskrat - Introduced and Exterminated

- Lecture 18: Ecology of the Water Vole - Ratty in decline

- Lecture 19: Wood Mice and Yellow-necked Mice

- Lecture 20: Control of Rats and Mice

- Lecture 21: Seals and Fisheries

- Lecture 22: Deer and Forestry