Badgers normally become sexually mature at 12 to 15 months old, although females may mature a little earlier ansd some males take as long as two years to reach maturity.
Badgers have unusual breeding patterns since mating can take place at any time of the year. The majority of matings take place between February and May, with another smaller peak of mating activity taking place between July and September. The female (sow) is receptive (i.e. in oestrous) for one to two days, during which she may mate with several males (boars).
A boar will go looking for a receptive female. Boars have been observed wandering round a sett sticking their nose into the entrance hole to scent the air for suitable sows; then making a churr noise to see if a female will come out. If there is no reply or the female remains underground; he goes to the next hole and tries again. If the sow emerges, she was then observed to be running rounds in circles. The male often pursues her making a shuffling motion with legs held stiff, his tail held vertically in the air whilst he makes a deep whinnying purr. The overall pursuit may last from 10 to 90 minutes. Encounters which are very short are possibly with inexperienced males or unreceptive females.
Note that this sequences of events may be repeated with different boars, meaning that the same litter of cubs may have the same of different fathers.
The egg is fertilised normally within the uterus and the fertilized egg is now called a zygote. This now enters the blastocyst stage, where it multiplies to form a hollow ball of cells (called a blastula).
Despite the presence of the first fertilised egg, female badgers still can have further matings with different dominant healthy males.
However, female badgers exhibit what is known as delayed implantation (sometimes called embryonic diapause). Diapause is a dramatic reduction in, or a cessation of, mitosis (cell division). This allows the blastula to be suspended in the uterus for between three and 15 months (15 months is very rare). Each blastula remains in a state of "suspended development" until the female badger has the chance to release a hormone which allows the blastula to move into the womb to implant at the end of December.
The chance to release a hormone is important, because if there is no hormone release the blastula may remain in suspended development until the next year; or it may be reabsorbed by the female and not progress at all. It has been suggested that the hormone produced by the female resides in her fat reserves. When the female goes into her winter torpor (in December), she lives off her fat reserves, allowing the hormones to be gradually released into her bloodstream, thereby causing the triggering of the blastocyst being implanted in the womb. Hence, under-weight sows may not have enough of the hormone to cause the blastula to implant in the womb. Underweight sows may not produce cubs (a good idea if her body condition is not in a good enough condition to produce healthy cubs that she could feed). Hence, it tends to be the more well-fed healthy sows that are more likely to produce cubs;and these are the ones who are more likely to survive.
Once the blastocyst is implanted in the womb, gestation is usually between six and eight weeks, with cubs born anywhere from mid-January to mid-March with the bulk occurring in early February (sometimes a little later as you go further north in the UK). Cubs born as early as December or as late as March are very rare exceptions. Unlike other mammals, the gestation period can vary if female badgers slow down or speed up their metabolism during their pregnancy.
Evidence from a large badger study by Oxford University has suggested that more than 90% of adult females are mated with each year. However, only about two-thirds of them actually progress to the gestation phase. Some of these are lost, so that only about one-third of sows actually give birth each year. A proportion of cubs die underground before they are mobile; so that perhaps only about one-fifth of female badgers produce healthy cubs which survive to weaning.
Importantly, in many clans only one female produces healthy cubs each year; although this can occasionally be two sows in beneficial conditions.
Effects on Badger Society Health
The effect of this somewhat complex method is that the female badger has more of a choice of which high-quality male(s) she can mate with, and that the date of the mating is no longer relevant to when the cubs are born. It is obviously better to have cubs born with well-fed healthy mothers so that they start being weaned when food supplies are becoming much more abundant.
When many people here about the winter torpor, they often think of it as something of a lazy time for badgers when nothing of any significance is hapnning. The truth may well be that this "quiet time" allows for sows to remain undisturbed so they can live off their fat, allowing the blastocysts to implant in the womb and gestation begin in earnest.
There is some evidence that setts which are disturbed produce fewer cubs than undisturbed ones.
New-born badger cubs are covered in grey silky hairs and usually the dark facial stripes are already visible. New cubs are about 12cm long (plus a 3-4cm tail), weigh about 75-130g and their eyes are closed for about 5 weeks. Badger cubs are fed on their mothers milk, and often live within a special nursery chamber within the sett. Their waste products are removed from the nesting chamber by the sow, until such time as they are mobile enough to use the latrines outside the sett.
Weaning usually begins when the cubs are at least three months old. During this time they feed on some solid food, particularly earthworms, and follow the mother when she goes off to feed herself.
Sense of smell is the most important sense for badger cubs, since the first two months or more of their lives are spent in darkness below ground where smell, hearing and touch are far more useful than sight. Even at three months old, the cubs are still very short-sighted. By following the example of their parents they also learn to use the "latrines" sited near the sett.
Dry, clean bedding is of great importance for the survival of the cubs. A chamber full of hay, straw and bracken acts as an efficient heat insulator, helping the cubs conserve their body heat. The straw will prevent the cubs being too battered by cold draughts; and it will insulate their bodies from the cold soil underneath where they lie down.