Secrets of the undergound set: Far from being the decent animals of popular imagination, badgers are vicious and share unusual sexual habits, says Nicholas Schoon
Monday 08 February 1993
The author of The Wind in the Willows also erred in portraying his badger as a solitary type. Badgers live in groups averaging nine members - six adults and three cubs.
But the mystery, according to Professor Stephen Harris, of Bristol University, is why these mammals bother living together. Other carnivores form groups to defend their territory from rivals, or to hunt prey larger than themselves.
But the badger's main food source is the lowly earthworm, which they hunt alone. They also defend their territory individually. 'Underground they sleep together, but above the surface they seem to do most things alone, apart from fighting,' Dr Harris says.
His research team estimates that a third of badger cubs falls victim to infanticide. The killers are other, dominant mothers from the same social group who slaughter the offspring of subordinates to ensure better survival prospects for their own young.
For their first year, the duration of a badger's childhood, the cubs lead a clandestine life, trying to avoid adult members of the group except for their own mothers. They spend most of their time underground in outlying burrows away from the main set (system of burrows) and do not wander far.
As a result, they forgo the grown-up badger delights of marking territory with faeces and urine, excreting underground instead.
The infanticide, like much badger activity, happens underground. For observers, the only direct sign is a dead cub left outside a burrow. However, studies have established that one-third of badger cubs do not survive their first three months, and it seems certain that the killers are other females.
Male and female adults within the same social group have a dominance hierarchy, which seems to be maintained through sometimes bloody fights, especially during the two mating seasons. The subordinates carry the worst scars.
'They have a powerful bite, which can cause severe wounds,' says Dr Harris, who has observed badgers since his teens and studied them professionally for 15 years. 'They tear big lumps of flesh out of each other's backs.'
In other social mammals and birds, a dominant male usually has exclusive sexual rights to several females.
Yet Dr Harris and fellow researchers from Bristol University and the Ministry of Agriculture have found that this is not the case with the badger. Subordinate males often succeed in mating with females on heat. And males from one group apparently tolerate younger strangers from other groups wandering into their set and blatantly cuckolding them.
Recent genetic studies by Oxford University researchers have shown that females often give birth to one litter sired by two males. This can happen because there are two mating seasons - in spring and late summer.
The first-stage embryos, known as blastocysts, that result from these couplings remain free-floating and tiny until the winter solstice; only then do they implant in the lining of the womb and begin to grow rapidly. The cubs are then born in February.
Much of the recent research on badgers has been funded by the Ministry of Agriculture, which needs to know more about the connection between tuberculosis in badgers and in cattle. Some badger groups have been studied intensively for years, with the animals carrying radio collars to allow their movements to be tracked. They are also lured regularly and harmlessly into cage traps to check on their health and breeding condition.
One research technique is to attach a spool carrying two miles of fine polypropylene line to a collar on the badger. During the badger's nocturnal wanderings, the line unravels through the undergrowth, showing the exact track the badger has taken.
A small amount of a fluorescent dye, fluorescein, is also injected harmlessly just below the skin. It spreads through the badger's body into the gut contents. By using a special ultraviolet torch, the researcher following the polypropylene trail can spot the glowing piles of excrement where the badger has marked its territorial boundary.
The other key source of information is badger corpses. Dr Harris and his colleagues have examined 650 dead females to find out how many gave birth and how many survived to suckle. Half were traffic victims; the remainder were animals lured into Ministry of Agriculture cage traps and then shot; badgers are still killed in an attempt to control cattle tuberculosis in south-west England.
Dr Harris believes the promiscuous and often bloodthirsty social life of badgers may be a peculiarly British phenomenon. Elsewhere in their range, which stretches from Ireland across Europe and northern Asia to Japan, they live at much lower population densities, have a more varied diet and probably live more solitary lives.
The research has not helped the badgers' reputation, but the scientists hope the public will continue their love affair with the mammals. Badgers are under threat from man-made damage to their woodland habitats, destruction of their sets and badger-baiting.
'The reality may be more grisly than children's books would have it, but badgers are quite a vulnerable species and they need help,' Dr Harris says. 'They're also intriguing - everyone thinks they know about badgers, but these animals have a secret, hidden life that we're only just beginning to understand.'
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