British Mammals
Overview
Artiodactyls | Carnivora | Cetacea | Chiroptera | Insectivora | Lagomorpha | Pinnipeda | Rodentia | Mammal Surveying

The largest and most populous group of mammals has an odd relationship with man. An irrational fear of small, furry creatures has driven many a householder onto the kitchen chair, and rodents are credited with everything from crop damage to spreading the plague.

However, rodents have always lived close to man. Humans provide warm homes and produce plenty of grains and waste for them to feed on. Rodents have been very successful in following travellers around the world, and there are few places left that they have not colonised, often to the detriment of the local fauna. Love them or hate them, rodents will never be too far away!

Rodentia is a very large order, and has been split into various sub-orders; in Britain, species belong to one of two Orders:

• The Sciuridae, the squirrels.
• The Myomorpha. This is divided into two 'Superfamilies' – the Muroidea (mice, voles and rats) and Gliroidea (dormice).

Rats

Easily the least tolerated and most frequently despised of Britain's mammals, rats have an uncomfortable relationship with people. While the visit of a mouse or squirrel to your bird-feeder may be amusing or cute, the sighting of a rat in the garden is likely to produce a rather different reaction. They have, however, made an unlikely stride in becoming popular pets!

Neither the brown (or Norway) rat Rattus norvegicus nor black rat Rattus rattus are native to Britain. Rats have been very successful in colonising anywhere man has visited, but frequently have an impact on the local wildlife – nesting birds in particular struggle to cope with their arrival, and where they are absent there are usually precautions to stop them taking hold. Notably, a Seabird Recovery Group managed to eradicate them from Lundy Island off the north Devon coast to protect important bird colonies. Rats' success is largely due to their habit of stowing away on ships, giving rise to the black rat's alternative name, the 'ship rat'.

Black rats were the first to arrive in around the 13th Century, coming into the country on trading boats from the Near East and quickly spreading across the mainland. They became infamous for the Black Death which affected most of Europe in the 14th Century, although some recent studies have suggested the black rat was not responsible after all. In the following century, the brown rat made an entrance, again introduced from abroad, and began to out-compete its cousin. Now, black rats are restricted to ports, where their numbers are believed to be boosted by more visitors from the sea; the brown rat dominates elsewhere.

Both species are infamous for the damage they can cause, not only to crops and in storehouses but also in people's homes. It is an uncomfortable truth that if your pipework or wires have been gnawed by rodents, it is likely to be the work of brown rats. Both species will eat almost anything, from insects and vegetable matter to house mice. While black rats tend to nest high up, in attics, behind pipes and even in trees, brown rats live around ground-level; for example, under floorboards or in haystacks. Brown rat burrows often have accompanying tunnel systems and runs.

Mice

Where there are humans, there are mice; although the converse is not necessarily true! Mice are everywhere; they live in our garden sheds, on our farms, in the woods, and are an important food source for larger predators. They can be distinguished from other rodents by their tails, which are at least as long as the rest of the body, and all have large ears and big eyes.

House mouse Mus musculus

This is the most likely mouse to be encountered by people and is believed to be the world's second most populous mammal. It has a fairly distinctive musty odour about it¹, and often heads closer to human habitation during the late autumn. You may find a house mouse in your shed, or even in your house - they can get in and out of holes about the size of a penny piece! A good way to see if mice can get into your house is to go round with a pencil and have a poke around skirting boards, underneath window sills and so on. If your pencil can get in, so can a mouse!

House mice are a uniform brown colour in the wild, and emit the 'classic' mousy high-pitched squeak.

Wood (or field, or long-tailed) mouse Apodemus sylvaticus

As its name suggests, the wood mouse is found in woody habitats; woodland, hedgerows and scrub. Whereas the house mouse is a uniform brown all over, wood mice have a white underbelly; when worried, they will often leap around manically or sit quietly, washing themselves with their paws!

Harvest mouse Micromys minutus

Agile climbers, harvest mice are great crop feeders, often feeding on grain in cereal heads - this is where they do most of their feeding, although crop damage is actually quite small-scale and rare. They also take berries and small fruits. They are the only British mouse to build nests above ground; a ball of woven grass about a foot off the ground is likely to be home to harvest mice.

Yellow-necked mouse Apodemus flavicollis

This is a much rarer cousin of the wood mouse; a little larger, more energetic and with a yellow band across its neck. Even though they are more agile and energetic than other mice, yellow-necked mice are believed to be in decline both in range and numbers across the UK, largely due to the loss of 'ancient woodland' habitat. They are only found in southern England and central Wales.

Voles

Voles are a much lower profile group than the other British rodents, but they are no less an important food source for larger creatures and feature the rarest rodent in Britain, the Orkney vole. The easiest way to identify a vole is by its tail, which will be half or less than half the length of its body.

Bank vole Clethrionomys glareolus

The bank vole is the most widespread of Britain's voles, occurring everywhere below 600m altitude except in the far north of Scotland. It is a small mammal, with very prominent ears, a lustrous red/brown fur and a tail measuring almost exactly half the length of its body. These voles are territorial and can be quite gregarious, and the strange clicking yelps of a territorial dispute have confused many a walker! Nesting in the ground in a series of tunnels, it spends most of its time at ground level but does occasionally climb trees and shrubs. It is omnivorous, eating green vegetation, fungi, nuts and berries and frequently snails. Food stores of these foods will probably indicate a bank vole nest is nearby.

Field or short-tailed vole Microtus agrestis

As their alternative name suggests, field voles have a much shorter tail, around a third of its body length. Its ears are well-buried in its fur.

Orkney vole Microtus arvalis orcadensis

In terms of the UK, it is odd that the Orkney vole is also known as the common vole - it is very common in Europe, but missing from all of the British Isles except the largest Orkney islands. It is a big vole species, almost twice as large as the field vole. It is currently believed that it was brought to the Orkneys by Neolithic settlers.

Water vole Arvicola terrestris

This is a large and attractive vole, with a rich brown coat that fades to pale grey underparts. It is, as its name suggests, an inhabitant of ditches and riverbanks, but has been recorded two miles from the nearest watercourses. It is a species of particular conservation concern, largely because of the recent spread of the American mink, which is the only predator able to hunt it on both land and water. Mink do not like living near otters, however, and the recovery of the otter population in recent years may help the water vole, as otters do not eat them!

Water voles have a rather taxonomically unsound alternative name, the water rat - 'Ratty' from Kenneth Grahame's The Wind In the Willows is actually a water vole - but rats and water voles are fairly easy to differentiate. Water vole fur is good at retaining air bubbles, so a swimming vole has most of its back poking above the water, whereas a swimming rat will show only its face. They may also be heard 'plopping' into the water, and riverside holes will show no runs² unlike rat homes.

Threatened by habitat loss and predation by American mink, numbers of water voles in the UK crashed from seven million in 1990 to less than a million in 1998 - and they are falling still; making water voles the UK's fastest declining mammal.

However, new proposals announced by DEFRA in February 2008 makes it against the law to intentionally kill a water vole or to recklessly damage or disturb the places they use for shelter or protection. This full legal protection should ensure a safer future for this attractive rodent, and hopefully populations will recover and thrive again.

Squirrels

Britons often use the phrase 'bright-eyed and bushy tailed' to describe someone who appears to be exceptionally squirrel-like – active and alert. These busy woodland citizens can often be found scurrying around in woodland, stashing the autumn nuts in preparation for winter, and the phrase 'squirreling away' is also used if one is saving money or stashing things away. Squirrels have an element of cheeky mischief in their behaviour; notorious raiders of bird tables, swinging from feeders and bombarding passers-by with nuts dropped from high in the boughs.

The plight of the red squirrel Sciurus vulgaris in Britain has become something of a cause célèbre in UK conservation. Its cousin, the grey squirrel Sciurus carolinensis, was allowed to escape in the late 19th and early 20th Centuries, and since then the red has rapidly declined and even disappeared from most parts of the UK. The grey squirrel outcompetes the red for food, being able to eat nuts when they are less ripe than the red requires; it also carries the parapox virus which is often fatal to reds. Red squirrels are only found in a few places now, and mainly on islands; the Isle of Wight, Anglesey and Arran are strongholds, as well as parts of mainland Scotland. Elsewhere, the grey appears to have completely outcompeted the red. The rapid disappearance of the red, considered one of our most attractive indigenous species, has caused much alarm.

Yet it may be that at some point in the future Britons may simply have to accept that the grey is here to stay. Eradicating it is unthinkable, considering the cost and effort this would require – the extermination of the South American coypu from parts of East Anglia alone took considerable investment and effort and still took six years. The march of the grey across the mainland is probably unstoppable, and it may be that conservation efforts could be better used in the far easier task of protecting those reds that are thriving on islands.

In fact, the red squirrel is very common across most of Europe, and Prof Stephen Harris quite rightly says that 'as a global conservation issue, it hardly registers'. The red itself was re-introduced from Europe in the 18th Century to supplant an ailing local population, and it may have been that the red would have declined almost as much without the grey. It has been claimed that greys cause much more damage to the local fauna than the more passive red - though it has to be pointed out that the holes made by greys are ideal for nesting birds. Times do change; these words were written about the red back in 1920:

[They are] one of the prime pests of the forester, for they destroy the young shoots of pine trees, remove the bark, devour the seeds and commit these enormities in overpowering numbers.
- James Ritchie, the Royal Scottish Museum.

The debate is likely to continue for some time. Britons will not simply give up on their red squirrels without a fight.

Dormice

The hazel dormouse Muscadrinus avellanarius is a fairly rare and protected species which is the focus of much recent conservation attention. It is another mammal that has found its way into descriptive language, being a creature that is fairly dormant for most of the year. Dormice enter a complete hibernation through the winter, their body systems shutting down so completely that it is very difficult to wake them up - in fact, the name comes from the French  dormir, to sleep. Dormouse workers, who require a training period and handling licence, have noted that they frequently remain asleep during handling and sexing! They are found most frequently in well-established woods, particularly where edible fruits of trees such as beech, sweet chestnut and of course hazel are found; however, they have recently been found in more unusual habitats, such as heath. It has also been found that they spend much more of their time in trees than previously thought, and nestboxes – long, thin tubes – are often put around nature reserves as an easy surveying technique. Honeysuckle is a favourite nesting material.

A second member of the Gliridae, the edible dormouse Glis glis, was introduced to the Chilterns in Hertfordshire by Lord Rothschild in 1902, and it has become established in the area without extending its range significantly (though frequent records from the New Forest come through). The odd name is true enough; they have been eaten in many countries since Roman times. It is most like a grey squirrel in appearance, but the significant difference is in the tail. The edible dormouse's tail is quite unusual in that the skin on it is easily detached; predators grabbing this part of the creature's body will often be surprised as the dormouse seems to slip out of it and make its escape! It can only perform this Houdini-like escape once, however, as the skin does not grow back.