It was warm, and hubby went in, because there was absolutely no activity in what we had hoped would be the hive that would make it, our 'big hive'. He found hundreds and hundreds of dead bees, no life at all. He checked all the way to the top of the bottom super (we are running all mediums, so three equals two deeps).
In the smaller hive, the one we fought to save back last June (see
this thread), a few bees rose up when he went in, so he didn't go any further.
We have mouse guards on both hives. I'm conjecturing that they got caught by the cold snap and couldn't get to their food. One of our beek friends said they probably had brood to cover and wouldn't leave it when it got cold. It was truly warm up until mid-January here, amazingly so, I don't doubt his theory. We've already bought replacement bees.