I always feel sorry for bees to be cooped up this long in the hive and
can't go for bathroom. Here it's even worse, from October till end of March.
2 died out of my 4 hives,...you're right it's been the worst winter here also as I remember, warm weather is still not around the corner.
It's hard to say what killed them...do you have them wrapped with insulation? At this time of year with low number of bees it's hard for them keeping warm...even with insulation.
Konrad

We did have them wrapped until a few weeks ago when it got warm for a few days. We took it off so the sun would warm the hive. Then I just put the tarp over the hive. Maybe I should have wrapped it more tightly.

It's hard to say for sure, I don't know how full your hive is, I use black
garbage bags outside, this warms up nicely when sun is out, better then
bare white hive.

I kept them wrapped tightly till it got to 80. After it cooled down I just had a tarp over them. They were alive and then they died. We took apart the hive, and they had plenty of food. I think they died from prolonged cold. Our coldest winter in a long time with no breaks. >>We ordered new bees and they will arrive in May. First hive we lost in many years. We ordered from Kelly. I'm guessing it's a good company??