Badgers are common over most of Britain, living in a wide variety of habitats (though they remain very secretive and elusive noctunal mammals).
The badger lives an underground home called a sett, which will typically be towards the centre of their territory or home range. Their setts are usually situated in or near small clearings in woodland or copses. Roughly 80% or so are in woodlands or hedgerows where trees or their roots provide the badger with some form of protection. The sett will be obvious to those who know what to look for, as the ground around the used entrances will probably be free of vegetation, and may be muddy and may show evidence of badger prints. There may also be evidence of latrines (holes in the ground) nearby, into which badgers do their poo.
They will also make setts in places such as old quarries/mine workings; and under buildings (especially in urban areas).
A simple sett is made up of a single tunnel, with a sleeping chamber at the end. However, most setts have several entrance holes, and lots of tunnels which link up with each other. The tunnels also link up with sleeping and nursery chambers. The tunnels may have several interlinking passages underground; and may also be arranged so as to provide a constant supply of clean fresh air through the sett in most weathers. Accordingly, entrances may sometimes be on different levels to help stale air rise through the sett and be dissipated into the surrounding woodland.
The tunnels may be excavated at different levels and at different depths under the surface of the soil. Some tunnels may be a dozen metres from an entrance and where natural air-flow is very low. In the same way that an underground train pushes a "plug" of air through the tunnels as it speeds through them; fresh air can come into these deep tunnels by the action of a badger rushing through the tunnels. The arched shape of the badgers back and the arched roof tends to make an adult badger force air into and out of the tunnels distant from an entrance hole.
Well-established setts normally have several entrances which are much larger than rabbit holes, and which have large piles of earth outside. The sett consists of large chambers for sleeping and breeding and small ones used as latrines, interlinked by a maze of tunnels.
A really big sett can have from 50 to 100 or more entrance holes. A sett this big will have been dug out by lots of badgers, over many years. There are some setts which are known to be over a hundred years old. Many generations of badgers have lived in these setts.
Badgers like to dig their setts where the ground is easy to dig. Sandy soil is a favourite, because it is easy to dig, and it stays drier than other soils. Chalk and broken limestone is also popular. Badgers do not like digging into clay, as this is wet and sticky. Even so, badgers will sometimes make setts in clay, if they can't find anywhere else.
They use their powerful front claws to dig and expand their homes. Their front claws may be 25mm long; and you will often hear them scratch on the ground if they are walking about on hard surfaces, such as roads, paving stones or block paving. Their claws on their back feet are shorter, as "only" 10 to 15mm.
Badgers also like to dig where there is a good slope, such as on the side of a hill, or in a bank. Water drains away better on a slope, and this means that the sett stays dry. Roughly 90% of badger setts are in areas of sloping ground.
Areas of flat ground pose a risk that the ground water levels may increase in the winter (due to rain) putting the tunnels and nesting chambers at severe risk. Whilst not usually a problem in the UK, tunnels are normally dug below the level at which the ground freezes.
Badgers dig their setts in many different habitats. Woodlands and hedgerows are good places to find badger setts, but badgers will also dig their setts in open fields, moorland, sand dunes, old quarries, abandoned mine workings and even sea cliffs! It is immensely important for a badger to feel safe in its home; and they will often dig setts or re-use old caves, mines, quarries, tips and old road/rail embankments. These can provide the badger with a really secure fortress which can protect the entire clan. Badgers will make great efforts to safeguard a main sett - in part because it is the best place for them to live locally; and also because they will have made a huge effort (in terms if work and time) to construct and expand the sett.
Certainly in the case of large setts, entrances to the sett may eventually lead back into random blind tunnels and a maze of interlinking routes between bedding chambers is generally found. Main setts may have tunnels at different levels; with the main nesting chambers 5 to 10 metres from the entrance and typically at least 2 metres below the ground surface.
Various species can share a badger sett - including woodmice, voles, rate, rabbits, weasels and even foxes. However, when foxes may share setts with badgers (and sometimes even raise their cubs there), it is unlikely that such sharing will be a long-term arrangement. The fox faeces, urine and food remnants frequently been found in fox dens are odious to badgers. This usually results in the badgers moving out or the badgers effectively forcing the fox to vacate the premises.
Nesting chambers within the sett are key to the comfort of the badger; as they provide a cool place to sleep during the summer heat; and they provide constant temperature in the cold winter temperatures. Nesting chambers are filled with bedding materials to keep the badger insulated, off the wet soil and to minimize draughts. This is especially important for small cubs, who would lose heat quickly, if they did not have warm bedding or if they were left out in the open.
For many years it was thought that nesting chambers were all formed at the end of a tunnel. Whilst it is true that most nests will be well away from the entrances, nesting chambers are often formed in a widening of a tunnel. A nesting chamber at the end of a long tunnel which is deep underground may not have enough airflow; and this could well explain why badgers sleep in widened tunnels rather than excavated rooms.
We expect that nesting chambers used by nursing sows are in a quieter part of the main sett. This would allow the sow the chance to keep other badgers away from her cubs. Nursing chambers need to provide easy access to the outside so that the sow can get in and out quickly; without the need to navigate through multiple tunnels and levels.
Nesting chambers vary in size and shape, but can be as small as 600mm in diameter. In other words, some chambers are too small to allow an adult badger to stretch out. Because nesting chambers can be so small, badgers often sleep curled up in a ball or together in nose-to-tail fashion. Such compact nesting chambers probably help badgers stay warm; especially as two badgers sharing a chamber will find it a lot easier to conserve their body heat. This is important in the winter; as there is little food; and badgers live largely off their reserves of fat.
Especially in a main sett, there will be rotation of the chambers which are in use. An individual chamber may be used for two or three consecutive days, before badgers move to use another chamber. This is done in rotation, so that over a periods of a few months, each chamber in a main sett may have been used. This rotation of nesting chambers means that each chamber has a chance to recover and freshen up; and so that any parasites which drop off the badger into the bedding have a chance to die off in the bedding rather than building up into a harmful load. Like many animals which have coats of fur or hair, badger can carry parasites, including certain species of ticks, fleas and lice.
The bedding materials may be gathered locally or up to 100 metres away from the sett. Good materials are taken down into the sett and used within a nesting chamber. Periodically the material will be brought out of the sett and left outside to "freshen up" in the daylight. Being in the daylight and any warmth may mean that it has the chance to dry out a little; as well as meaning that any parasites within it either leave or die off. Bedding may remain outside for a few days; before being taken back underground. Bedding materials can be re-used repeatedly - sometimes for as long as 12 months.
Inside the sett, the air temperature pretty much remains within the range 6 - 19 Centigrade throughout the entire year. This is true even if the outside temperature is well below freezing or if there is a major heatwave. The main factor which determines the minimum and maximum temperatures inside the sett is the vegetation cover around the entrances. Setts within woody cover have the most stable internal temperature profiles.
Pretty much all setts have close to 100% humidity inside, which probably accounts for the bedding materials being taken out to freshen up (and dry off) periodically.
In the UK, the following sett categories are recognised:
Outside the UK, there is a tendency to identify a badger sett as "main" or "other"; which is a bit simpler. Importantly, the designation of a sett may change over time. Some setts may become abandoned by badgers; and fall out of use. In other cases, badger territories may change; and a non-main sett may be upgraded by being converted into a main sett. The conversion of a non-main sett into a main sett does not always mean that there are more badgers in the locality, as they may have move out of their main sett into another sett which they use as a replacement main sett.
These usually have a large number of holes with large spoil heaps, and the sett generally looks well used. They usually have well used paths of compacted bare earth to and from the sett and between sett entrances. Although normally the breeding sett is in continual use, it is possible to find a main sett that has become disused because of excessive digging or for some other reason, in which case it is recorded as a disused main sett. A large main sett may contain small amount of dung. This will be found in discrete corners of the sett complex, although not to the extent seen in the dens of -- or parts of the sett used by -- foxes.
These are always close to a main sett, usually less than 150 m away, and are usually connected to the main sett by one or more obvious, well worn paths. They consist of several holes, but are not necessarily in use all the time, even if the main sett is very active.
These often these have only a few holes, are usually at least 50 m from a main sett, and do not have an obvious path connecting them with another sett. They are not continuously active.
These usually only have one or two holes, often have little spoil outside the hole, have no obvious path connecting them with another sett, and are only used sporadically. When not in use by badgers, they are often taken over by foxes or even rabbits. However, they can still be recognised as badger setts by the shape of the tunnel (not the entrance hole), which is at least 250-300 mm wide at the base with a rounded or flattened oval roof (roughly 200 mm high).
Over a period of decades, main setts can expand so they become even more obvious structures, with up to 100 entrances, with tens of tonnes of excavated material in substantial spoil heaps and hundreds of metres of underground tunnels.
In some cases; the badgers may adopt a pattern of digging new tunnels and entrances at one side of the sett. In these cases, it is not unknown to see a main badger sett "move" tens of metres over a period of decades. Whilst this may seem a curiosity; it can cause problems if the sett starts to encroach onto gardens, golf courses and under roads/railways or buildings. In circumstances like this, when badgers are beginning to cause human problems, the people affected need to contact their local Badger Group or a specialist Badger Consultant.
Importantly, the digging of new setts and tunnels is not done equallly by all badgers. Oxford university found that, in their area, 20% of clan members were responsible for 60%-90% of the digging and bedding collection. Males (especially males of higher social status) tended to do more digging. It has been suggested that dominant males would expand the number of nesting chambers as this would make it easier for them to maintain a "harem" of breeding females within the same large sett. Both males and females more or less shared the need to collect new bedding materials, but that breeding sows made more effort to maintain high-quality bedding materials.
The combination of different setts in a single territory is interesting; as this can vary with the size of the territory, the size of the clan a food availability. Very large territories with poor food supply can mean that there are relatively more outlying setts. It is suggested that this is because the badger needs to spend more of its time looking for food; and it will make use on a distant outlier sett as an occasional shelter rather than be faced with a long trip back to the main sett every day.
Badger setts are often used by other animals as well as badgers. Rabbits often live in badger setts. Foxes will also rear their young in setts. These animals live in small setts, or parts of larger setts, which are not being used by badgers at the time.