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RSPCA - Problems With Badgers?
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2. BADGER BIOLOGY

2.1 Badger numbers and reproduction
2.2 Badger setts

2.1 Badger numbers and reproduction

Badgers are widespread throughout mainland Britain, and a recent survey estimated that there are 42,000 social groups of badgers in Britain. There are probably slightly more in Ireland (around 50,000). In Britain this means that there are about 250,000 adult badgers, and 175,000 cubs are born each year. However, these badgers are not uniformly distributed, and they are less common in upland areas, East Anglia and parts of northern England. They are also found on three of the larger off-shore islands: the Isle of Wight, parts of Anglesey and the island of Arran. In some areas badgers can be very common, particularly in the south and south-west. In one area of the Cotswolds it was calculated that the badger density was approximately thirty adult animals per square kilometre (one third of a square mile), although in most rural areas densities are much lower than this. In Ireland maximum densities, in terms of the number of social groups per square kilometre, are similar to those in Britain, but the distribution is much more even. This explains why there are more social groups of badgers in a much smaller area. However, mean group size in Ireland appears to be a little lower than in Britain, and so the overall number of adult badgers is about the same i.e. about 250,000. Badgers frequently enter gardens on the edges of towns and villages to forage or to be fed by the local householders, and there are even resident badger populations in a few cities. In one part of Bristol, for instance, there are more than ten adult badgers per square kilometre, although such large numbers living in an urban area are very rare.

Some basic knowledge about badgers is necessary in order to understand the problems that may arise and how best to tackle them. In areas where badgers are rare, they may be solitary or live in pairs, but in most of Britain badgers live in social groups of approximately five to twelve individuals. A typical group contains male and female adults, sub-adults and cubs. The sex ratio is approximately equal at birth, but mortality of males is higher, and so there is usually a preponderance of females in the adult population. Each group of badgers normally produces one litter of cubs per year, but two or three different females may sometimes breed in the same year. Female badgers show delayed implantation; mating can occur during most of the year, but the fertilised egg only develops to the blastocyst stage (which is a very small ball of cells). It then remains in this state for several months before implanting in the wall of the uterus in early winter and developing into a foetus. The usual time for implantation to occur is December.

Although badgers do not hibernate, they are less active above ground during much of December and January (although they are often very active below ground), and may not emerge from their sett for several consecutive nights. Even when they do emerge they may eat very little, and they live largely off fat accumulated in the autumn. During this period the female is sensitive to disturbance and, if the disturbance is serious, implantation might be delayed or the blastocysts lost. Cubs can be born as early as the second half of December, although the peak period is during the first fortnight of February. The majority of cubs are born by early April.

Badger cubs stay below ground for at least eight and sometimes nine or ten weeks, and weaning begins at about twelve weeks, although lactation may be extended in hot dry summers. Most cubs therefore are weaned by early May and almost all by the start of July, although they may continue to be dependent on, and sometimes forage with, their mother for some time. Litter size ranges from one to five, although two or three is most common. In lowland Britain earthworms are the most important food item, although cereals and fruit may figure significantly in the summer and autumn diets respectively, and scavenging is important in urban areas.

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2.2 Badger setts

In most cases each social group of badgers has more than one sett in its territory, and these vary in status and level of use (fig.1). Whenever there is a badger problem in an area, it is essential to undertake a thorough survey to establish (i) how many social groups may be involved and (ii) the distribution and status of any setts being threatened. The extent of any problem depends on the type of sett under threat, and so the different types of badger sett occupied by a single group of badgers are described below:-

a. Main setts: Normally each group of badgers has only one main sett, and so by counting all the main setts in an area you can find out how many social groups of badgers are present. Main setts usually have several holes with large spoil heaps, and the sett generally looks well used. There will be obvious paths to and from the sett and between sett entrances. In the British national badger survey the average number of holes for a main sett was twelve, although main setts may be much smaller, even a single hole in exceptional circumstances. Although normally the breeding sett, and in continuous use, it is possible to find a main sett that has become disused due to excessive interference, illegal digging, tree felling or some other reason.

b. Annexe setts: These are often close to a main sett, normally less than 150 metres away, and are connected to the main sett by one or more obvious well-worn paths. Usually they have several holes but may not be in use all the time, even if the main sett is very active. The average number of holes per annexe sett in the British survey was eight.

c. Subsidiary setts: These are usually at least 50 metres from a main sett, and do not have an obvious path connecting with another sett. They are not continuously active. The average number of holes per subsidiary sett in the British survey was four.

d. Outlying setts: These often have little spoil outside the holes, 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 actual entrance hole), which is at least 25 centimetres in diameter, and rounded or a flattened oval shape (i.e. broader than high). Fox and rabbit tunnels are smaller and often taller than broad. The average number of holes per outlying sett in the British survey was two.

Fig 1. Territory of badger social group showing distribution of sett types
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