The Mammal Society - the voice for British mammals

Studying the mammals in your garden

Which species visit your garden?

Perhaps the hardest job is to know which species of mammal are visiting your garden. Some, such as squirrels and hedgehogs, may be pretty obvious, whereas other visitors are far less conspicuous. Small mammals stay in dense cover, bats are not easy to see other than the occasional sighting at dusk, and foxes, badgers and deer may visit late at night after most people have gone to bed. So even knowing which species visit your garden is not easy. The best ways to identify the different types of mammals visiting your garden are described below.

Studying small mammals

The commonest small mammal to be found in British gardens is undoubtedly the wood mouse, and this species penetrates well into built up areas, although it is commoner closer to patches of woodland and scrub. In southern England and the Welsh border counties, yellow-necked mice may also be seen, especially in gardens close to woodland. House mice are most common in city centres, and voles and shrews tend to occur in larger gardens with plenty of ground cover, especially those close to woodland or rough grassland.g your garden it is probably best not to feed the hedgehogs as well.

Setting up a small mammal table
Most species of small mammal, other than wood mice and yellow-necked mice, can be told apart by sight. The differences in size and appearance are described in the Key to British land mammals - see further reading. Seeing them, however, is not easy since most species of small mammal prefer to hide in dense cover. The best way to get to see them is to build a feeding table below a window. This needs to be in a cat-proof free-range enclosure built around the window. The enclosure needs to be made of very fine mesh - less than a centimetre mesh to keep birds out, and with entry points either at ground level, or through small pipes, or even through underground pipes. These holes should be no more than 3 to 4 centimetres diameter or else you may also attract rats. Two types of food should be put out - a general mix of seeds sold for wild birds, peanuts and castors (fly pupae) obtainable from a fishing shop. The rodents will eat all of these, but the shrews will only eat the castors.

Cover inside the enclosure makes it particularly attractive to small mammals, and there needs to be plenty of cover leading to the enclosure so that the small mammals can travel to and from it in safety. Scrub or bushes, preferably underplanted with dense grass, connecting to a nearby hedgerow or patch of wasteland or woodland is ideal. At night the light from the window will illuminate the feeding table, but as soon as the small mammals become accustomed to using the table, and are aware that they are safe from predators, they will also appear during the day. Bank voles are likely to be seen most frequently during daylight, followed by shrews. But even largely nocturnal species such as wood mice will also be seen during the day once they feel safe. The only species that is unlikely to visit a feeding table such as this is the field vole, but if there is plenty of rough grass in the enclosure, a colony of field voles may become established and be seen feeding on fallen grain under the table. An arrangement such as this will allow most species of small mammals to be seen and identified without the need to catch them.

Trapping small mammals
The alternative way to find out which species of small mammal are using your garden is to trap them. The correct way to do this is described in Live trapping small mammals - a practical guide (see further reading). The important thing is ensure that there is dry bedding (a small handful of hay is best) and food (clipped oats for the rodents, castors for any shrews) in the trap. Also, to ensure that no animal remains in the trap any longer than is necessary, the traps should be inspected last thing in the evening and as soon as possible after sunrise in the morning.

Various types of trap are available, but the plastic traps (Trip traps) available from many pet shops should not be used. These are designed for use indoors and if used outside any small mammal is likely to die of cold or wet. The traditional trap that has been used for half a century is the Longworth trap, but these are very expensive. A similar but much cheaper trap is the Wellfield trap, and these sell for around £25 each (see trap suppliers at the bottom of this page). Although the booklet Live trapping small mammals - a practical guide was written before Wellfield traps were available (and hence only talks about Longworth traps), the advice applies equally to both types of trap.

The traps should be scattered around your garden and any small mammals caught tipped out into a large polythene bag to aid identification. However, it is also interesting to find out how many small mammals are using your garden and this can be done by trapping continuously for a few days and marking all the animals that you catch. This is done by carefully manoeuvering each animal you catch into a corner of the polythene bag, then taking hold of it by the scruff of the neck and taking out of the bag, or by holding it in the corner of the bag and exposing its back and rump. Then cut a piece of fur with a pair of small sharp scissors, so that you leave a recognisable mark. You do not cut the fur off completely, but simply trim the fur back to expose the greyer underfur. Marking each animal in a different place (and when you run out of options, you can then mark animals in two places) enables you to recognise each individual animal that you catch. Continue this process for a few days until you catch few or no new animals. This tells you the minimum number of each species of small mammal using your garden.

Using hair and footprint tubes
An alternative, and much cheaper approach, is to use hair or footprint tubes. These will not enable you to identify the exact species of small mammal or estimate population size, but they are extremely useful in that they will allow you to find out which bits of the garden the small mammals are using. This is extremely useful information - once you know which parts of the garden they frequent most often, you can then see which habitats the small mammals are selecting. Generally this will be those parts of the garden with good ground cover, but it may also be areas with lots of seed and/or berry-producing bushes. By knowing which habitats the small mammals frequent most often, you can then look to improve the other parts of your garden for small mammals. Once you have made these improvements, you then need to continue monitoring the levels of small mammal activity in these parts of the garden to see if your efforts have been successful.

Both hair and footprint tubes are made from plastic overflow pipe 45 millimetres in diameter that can be obtained from any hardware shop. To make footprint tubes, the pipe should be cut into 30 centimetre lengths, for hair tubes 10 centimetre lengths. For the footprint tubes, two inkpads needs to be placed at each end a little way inside the tube. To make these, a piece of greaseproof paper about 7 by 4 centimetres is stapled widthways onto each end of a sheet of plain paper. Then children's poster paint (this is non-toxic) is mixed with an equal amount of vegetable oil to prevent desiccation and then brushed on to the greaseproof paper. The paper and inkpads is then slid into the overflow pipe, lining the bottom with the pads central, and a chunk of peanut butter placed halfway down the tube so that it clings to the top. The tubes can then be scattered around the garden and left overnight.

Foot Print Tube

Hair Tube

For the hair tubes, a slot needs to be cut in the middle of each end of the tube to fit a piece of sticky tape across the tube. A blob of peanut butter bait should be put in the middle of the top of the tube as with the footprint tubes. The tubes then need to be scattered around the garden (with the sticky side of the tape facing downwards, of course) and left in position for a few days. The length of time the tape remains sticky depends on the weather, but for a few days it will catch hairs from the back of any small mammal entering the tube.

Both techniques are very useful for monitoring small mammal activity but not for identifying the species of small mammal present. The footprints of "mice", "voles" and "shrews" can be told apart - use A key to mammal tracks and signs (see further reading) to do this. Hair identification is not easy, and requires a specialist key and equipment. However, exact species identification is not necessary. You can establish the actual species present in the garden from observations at a feeding table or by trapping, and then use the tubes as a quick and simple way to establish whether your attempts to improve the garden for small mammals are being successful.

Studying bats

These are probably the most elusive group of garden mammals. It is also important to remember that all species of bat are fully protected and so the advice given here simply describes activities that can be undertaken without a licence. Whilst many gardens are visited by bats, visits are often brief and infrequent, and sightings even rarer. The best chance of getting a good view of a bat is at or soon after dusk, especially if a roost is nearby. Identifying species in flight is not easy, but The Mammal Society is producing a guide to identifying bats in the field and this will be available shortly.

The best approach is to buy a bat detector and listen to their echolocation calls. Several types are available and advice on the best one for your purpose can be obtained from Alana Ecology (see website links). Learning to identify the calls takes practice, but there are several books describing how to do this. The bat detective - a field guide for bat detection (see further reading) is particularly useful because it comes with a CD with recordings of most species of British bat. Once you have learnt to recognise the calls of most species of bat, you can use the detector to monitor the species of bat using your garden (and how often they visit) and the bat activity in your local neighbourhood.

It is also useful to put up bat boxes, since these may attract bats to your garden. Advice on how to construct and site bat boxes can be obtained from Bat boxes - a guide to the history, function, construction and use in the conservation of bats (see further reading). Erection of bat boxes is best done in collaboration with improving the habitat in the garden for bats, and advice on how to do this is given in the Habitat management for bats - a guide for land managers, land owners and their advisors (see website links).

Further advice on the law relating to bats, and how to study them, can be obtained from the The bat workers' manual - see further reading.

Studying larger mammals

Using field signs
Some of the larger mammals visiting your garden are easy to see - squirrels are all too obvious, especially if you feed the birds in your garden. Hedgehogs are also generally easy to see, especially if they are fed regularly. Other species are more elusive, but will leave signs of their presence. These generally take one of three forms: droppings, tracks or fur on fences and other points where they enter the garden.

Faeces are generally easy to identify and these are illustrated in A key to mammal tracks and signs - see further reading. Probably the biggest problem will be identifying badger droppings. Many text books say that these are always left in shallow pits, but often this is not the case, especially in gardens. Generally, however, it is easy to recognise the droppings of those species of mammal most likely to visit your garden. If you are concerned about these posing a health hazard to your pets or children, the risk is low, but simply remove the droppings by putting your hand in a polythene bag, picking up the dropping, sealing the bag and putting it in the bin (and wash your hands afterwards!).

Tracks are also generally easy to identify, but it can be difficult to get good footprints. There are two ways to tackle this problem. You will often see where the larger species of mammal are entering your garden - they will squeeze through a hole or dig under a fence. Or there may be a conspicuous path into the garden. Once you have identified the main entry points, place a sand trap at each of them. Get some fine sand, moisten it so that it holds a clear impression of the footprint, and spread a layer about a centimetre deep over the ground. Check the sand traps each morning, measure and photograph or trace any tracks that you find, and then smooth the sand over again and moisten it if necessary. The tracks can then be identified using A key to mammal tracks and signs.

If you suspect that you have stoats, weasels or even polecats visiting your garden, the easiest way to get tracks is to make a larger version of the footprint tube described for small mammals. The diameter of the pipe needs to be around 10 centimetres, length around 45 centimetres, and the tracking pad covers the length of the tube. You do not need any bait, but scatter these pipes around the garden in dense cover, along the edge of walls, etc. The problem identifying the footprints is that these small mustelids show a high degree of sexual dimorphism (the sexes are very different sizes, with the males being a lot larger than the females); male weasels are similar in size to female stoats, and male stoats to female polecats. So from the tracks alone it is rarely possible to be absolutely sure which of the species is visiting your garden. However, once you know that they are there, you can then use a camera trap (see website links) or watch to see which species is present.

If you find hairs snagged on your fence, you may need help identifying these. The most likely option is your neighbour's cat. Badger hairs are easy: they are coarse and the hairs on the back are up to 10 centimetres long and black and white, although those on the face are a lot shorter and can be either entirely white or black. A key feature of badger hairs is that they are oval in cross-section and "turn over" when rolled between finger and thumb. Fox fur is silky to the feel, with the guard hairs composed of black, yellow-brown and white bands, the proportions of which vary according to the part of the body. The underfur is finer and grey in colour.

Watching mammals in your garden

The easiest way to do this is to provide regular food. Most mammals will become extremely tolerant of people when they feel secure, but it is important not to make them too tame. So feed and watch them from a distance. There are proprietary foods available for badgers and hedgehogs (see website links), and foxes and badgers will eat a wide range of meat and other household scraps. Both species have a sweet tooth, like peanuts, cheese and bread cooked in fat. Deer (and rabbits and hares) will visit gardens to eat the garden plants, but can also be attracted by providing root crops during the middle of winter - chopped carrots, potatoes, swedes, etc. are highly attractive when food is short and/or the ground frozen.

When you start feeding, it may be some time before the food is taken regularly, but persist so that the animals get used to coming to your garden each night. Foxes and badgers in particular will soon settle into a routine of being fed, and may even be sitting outside waiting for you to put the food out each evening. Deer tend to be more secretive, and dawn is often the best time to see them. All these species can also be habituated to low levels of lighting, but this is generally not necessary and can make the animals wary. If you want to watch their natural behaviour, the best approach is to leave the lights on upstairs, so that there is a low level of lighting across the garden, and watch from downstairs in a darkened room downstairs using a reasonable pair of binoculars. These have good light-gathering powers and you can see perfectly clearly in low light levels without disturbing the animals or making them aware of your presence.

How many mammals visit my garden?

With time and patience, this question is not too difficult to answer, but your first impression is likely to be a significant under-estimate. Grey squirrels are the most conspicuous of the larger mammals, but rarely all visit together. But by watching their behaviour and recording fur colouration, bushiness of the tail, bulk (the younger animals generally look a little less heavily built), nipples or testes when you see these, nicks in the tail, etc., you can pretty soon work out how many squirrels are using your garden. And you are likely to be surprised (or depressed if you are wondering why you are loosing so much of the food you put out for the birds).

Hedgehogs are a little more problematic because they are not territorial and so you may have several different animals visiting your garden even though you generally only see them one at a time. Some animals can be recognised individually, but this is not easy and generally not reliable, especially in poor light. The best way to do this is to mark the hedgehogs with a non-toxic spray paint or hair dye. You can use different colours for each hedgehog, or mark different part of the body with the same colour. A key for doing this is given in Hedgehogs (see further reading). Pale colours are easiest to see at night by torchlight, but it is vital to ensure that you keep the paint away from the animal's head.

Nocturnal species such as foxes and badgers can be a little more tricky to count, especially if they visit late or throughout the night. Badgers are generally the easier of the two to recognise individually. Variations in the shape of the facial stripes, whether they have white tags on the ears (these are often lost in fights, so are more often seen on younger animals), size of the animal (boars are generally bigger, more heavily built, with a more domed head) and shape of the tail all enable you to build up an identification key for the badgers that visit your garden. This is well illustrated in Badgers (see further reading).

A similar range of features can be used to recognise individual foxes - males are generally slightly bigger than vixens, the colour and extent of silvering on the rump is variable, as is the size of the white tag on the tail. Also, males tend to have a broader and heavier head, and when seen face-on the ears tend to form a "W" shape on the head whereas for a vixen it is more of a "V" shape. In the winter, the male's testes enlarge and can sometimes be seen protruding from behind the hind legs (the scrotum also becomes hairless at this time of the year, making it more obvious), and in May and June the teats of a lactating vixen are generally obvious, especially those at the rear of the abdomen (these are generally larger and better developed that the front teats). However, it is important to remember that relying on appearance to recognise individuals is not infallible. Foxes, for instance, live in family groups and the young (especially but not invariably the females) stay in their natal group as an adult. Mothers and daughters and fathers and sons can be extremely difficult to tell apart.

It can also be difficult to see all these features if an animal only visits briefly or occasionally. Photographs can be a great help in enabling you to check features later or to compare different sightings. This can be easy if the animals visit in daylight or are habituated to your presence. Alternatively, you can set up a flash camera in the garden and take photographs remotely; the animals soon get used to the camera noise and flash. You need a camera that winds on automatically so that you can take several photographs in a single night. However, you can still miss some of the animals if the dominant animals visit early in the night and the subdominants only come later after you have finished watching. The only way to know if this happens is to use a remote camera trap. Although these are expensive, they are well worth the money and provide a wealth of additional information about the animals that visit your garden (and if you have a cat problem, you have the photographic evidence with which to confront the owner!).

Remote photography has many advantages for studying the mammals that visit your garden. The units can be left unattended for some time, and usually the animals are not concerned by the flash or quickly return after the initial shock. One widely-used camera trap is the Trailmaster 1500 infra-red game monitor and TM 35-1 camera kit. The Trailmaster consists of two separate units that transmit and receive an invisible infra-red beam. The system is connected to a camera. Each time the infra-red beam is broken by a passing animal, the Trailmaster records the date and time, and the camera takes a photograph of the animal. The Trailmaster can be programmed only to take photographs at particular times of the day or night, depending on when you think animals visit your garden (and to reduce the number of photographs you get of the neighbourhood cats!). Also the height of the beam can be changed so that only animals of a particular size are recorded. The set-up can be altered to target slow or fast-moving species, and it can be programmed so that there is a large time delay between photographs. This reduces the chance of photographing the same individual twice. All these refinements can increase the chance of photographing all the animals visiting your garden.

The camera traps should be positioned where they have the greatest chance of being triggered, such as across well used tracks or feeding areas. They should also be moved frequently in case some animals do not use the areas you are monitoring.

The camera unit recommended above is cheap and has an integral flash unit: the photographs are adequate but not high quality. In the safety of your own garden you may prefer to use a much more expensive camera with separate flash units, as shown in the illustration, but then you need to fix an umbrella above the camera to protect it from rain.

When setting up the camera trap, it is important to remove any vegetation that lies between or near the transmitter and receiver units, because wind will blow nearby twigs and branches into the infra-red beam. On a windy day you will get a lot of blank photographs! It is also important to ensure that the objects, such as trees, that the Trailmaster units are attached to do not move in the wind, since this may result in the beam being broken, or blurred photographs. One other potential problem is that pets or wild animals may chew the cables. This can generally be prevented by lifting the cables off the ground and tying them to canes pushed in to the ground.

Camera traps are also extremely useful in helping you identify the individual deer that visit your garden. The two commonest garden species are muntjac and roe, and it can be very difficult to recognise individuals of both species (especially the females), since they have few distinguishing marks. However, since both species are territorial (all year for muntjac, during the summer for roe), only a few individuals are likely to visit your garden. This makes individual recognition easier.

The Mammal Society - the voice for British mammals, and the only organisation solely
dedicated to the study and conservation of British mammals.

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