The secret life of Ireland’s badgers

Driving at night, you may glimpse a badger dazzled by the car headlights. Otherwise, this creature of the night is seldom seen, writes Richard Collins. 

‘Broc’ values his privacy and this makes aspects of his life very difficult to study. Nonetheless, researchers were sure they had unlocked most of the badger’s secrets, until a paper published this month showed that they haven’t. New tracking technology has revealed social behaviour far more complex than was previously recorded. According to co-author David Macdonald of Oxford University, “the private lives of badgers turn out to be almost as hard to understand as those of people”.

Although badgers in Scandinavia and southern Europe tend to live in isolated pairs, Irish and British ones prefer extended families. The greater abundance of earthworms and insect larvae here may explain this; our badgers form ‘clans’ to better exploit these resources. There may be ten or more adults, of both sexes, in a network of tunnels and chambers known as a ‘sett’. One British ‘clan’ had 29 members.

Family groups, whether extended or not, were thought to be strongly territorial. Males marked the limits of their clan’s territory and defended it against all intruders. Few individuals, it seemed, ever travelled beyond their home-range boundaries. This had implications for TB culling programmes. It was claimed that targeting a sett would not cause badgers to move elsewhere, spreading the disease. The isolationist tendency also had implications for proposed vaccination programmes.

Indications that badgers are not so sedentary came to light in a study carried out by zoologists from Trinity College Dublin.

Satellite-tracking collars were placed on 50 badgers in Wicklow. Each device recorded the location of the animal wearing it on about four occasions during the night. The badgers, it was found, avoided farmyards and fields in which cattle were grazing but they were indifferent to the presence of horses. They also travelled much more than expected. One individual covered a distance of 9km in three hours.

GPS collars reveal much about badger movements but they can’t tell us how the animals relate to each other or what happens when they encounter individuals from other setts. To tackle this problem, researchers at Oxford and Cambridge Universities sought the help of computer scientists. The combined team used state-of-the-art surveillance techniques to study badger interactions near Wytham in Oxfordshire.

 

Active Radio Frequency Identification Technology was developed to protect art works in museums. It can also monitor the progress of tweets on mobile phone networks. “Tracking the way a tweet goes viral is a staple of the modern world and says a lot about how interconnected people have become through our use of information technology,” Stephen Ellwood, lead author of the paper, told Science News.

Using this technology, his team were able “to build up patterns of inter-group connectivity beyond those previously understood”. The researchers studied the comings and goings of badgers using ‘base stations’ at key locations, such as ‘latrines’. They recorded the extent of contacts between individuals and how long they spent in each other’s company. The detection range was 31.5m.

Badgers, it turns out, regularly travel beyond their territorial boundaries. They are not anti-social but readily tolerate visitors from outside. Interactions between differing social groups are much more extensive than was previously thought; 20 to 100% of tracked badgers ‘engaged in inter-social mixing’ each week. Up to half of cubs are fathered by males not belonging to their mother’s sett.

According to David Macdonald, “We are nudging closer to an understanding that is not only intriguing but also, for example in the context of bovine TB, useful’.

  • Stephen Ellwood et al. An active radio frequency identification system capable of identifying co-locations and social-structure: validation with a wild free-ranging animal. Methods in Ecology and Evolution. 2017.



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