Why do badgers give birth in winter?

Badgers mate in spring, then delay producing cubs for months. But why?

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Female badgers give birth to their cubs in winter © Dirk Freder / iStock

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Much of what we know about badger ecology comes from long-term studies at Wytham Woods near Oxford and Woodchester Park in Gloucestershire, where scientist Steve Carter of the Animal and Plant Health Agency is based.

“In winter badgers don’t hibernate, but spend far more time in their setts so we see them less,” he says. “They do emerge to forage in mild weather, generally being more active further south and if they are regularly fed by people.”

Despite female badgers eating less and living off fat reserves, winter is nevertheless when they give birth to their cubs, which are helpless, blind and barely 12cm long, with a 3–4cm tail. Yet this makes sense in the long run, explains Steve.

“The aim is for the cubs to start venturing above ground in April or early May, when invertebrate food is plentiful and they have as much time as possible to put on fat to prepare them for their own first winter. To get this timing right, female badgers must give birth between January and March, with February usually the peak month in Britain.”

Pregnancy lasts six to seven weeks in badgers, so it follows that sows need to fall pregnant in December. But mating normally takes place in spring or summer. The solution is delayed implantation. “Each blastocyst, the tiny ball of cells that becomes an embryo, does not implant for several months,” says Steve.

“Interestingly, a female badger may mate with more than one male and bear a litter of mixed parentage. She can also ovulate a second time and mate again while already carrying blastocysts from an earlier mating, and still start the pregnancy at the same time to produce a single litter of cubs. This remarkable ability is called superfetation.”

Did you know?

In northern Russia badgers seldom leave their sett in winter. In southern Spain, however, they remain fully active since their main food – rabbits – is still easy to find.

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