They don’t seem too bothered by the cold. The ones who don’t hibernate still turn up on really cold nights i.e. -5 or sometimes more. The hogs here aren’t showing any signs of missing visits on cold nights, once they are back. Nor have they in previous years. Which is a pretty good indication that temperature alone, is not necessarily a trigger for hibernation or return from it. But when they first return it sometimes takes some of them a little while to get their metabolism ‘speeded up’ again, so they might miss a night or two.
Some of the males who are around at the moment are likely to have started hibernation before it got really cold. They always seem to hibernate earlier and return earlier than the females and there is some sense in that behaviour. It enables them to regain sufficient body weight after hibernation before the females return and they begin to use a lot of energy during courtship. But females often have hoglet rearing duties continuing well after the males have ‘disappeared’, so it’s not surprising that they tend to return from hibernation later than the males as well. (Sometimes as much as 2 months). It seems nature is very clever at arranging things.
There are, of course some exceptions, i.e. there may be some females who choose not to hibernate, or who came out of hibernation earlier for some reason and the previous year’s hoglets might also return earlier – male or female.