Tempature and food availability, in my youth when winter was winter and men were men???ok enough of that shit, but when there was proper snow on the ground and digging was still legal, I would go and check setts for activity when there was snow on the ground and the badgers would often remain indoors for two weeks without breaking cover, at this time of year now they are building up fat after winter, so next big signs will be when the leather jackets hatch that’s when they will plough a field overnight like pigs everything in nature follows a sequence there is no point wasting energy looking f