I'm new at bee keeping, I've got 4 hives and all have made it through the winter so far. I am concerned about 1 of the hive. The bottom board had a lot of dead bees. The other hives have very few dead bees. The weather has been cold all through January very few days above 30 deg. I raked out a little more than a pint of bees last weekend. When temps got above 50 this week hive seemed as strong or stronger than other hives. Bees have plenty of supplies. What should I look for? Thanks for all the help!!!