Brood activity begins long before there is much to do outside of the hive.
First things first. Are the bees alive and healthy? Hopefully they are because then they can proceed to produce the first frames of brood to start boosting the bee population. Getting new bees is important as the overwintered bees get older by the week. This also lets us know the queen is not only present, but doing what she does best, laying eggs.
New brood is a good sign for the survival of overwintered beehives.
It is nice to start seeing good patches of brood here in March. The weather has so much to do with how the bees come out of the winter months. And Iowa weather can be crazy in March. Well, actually about any month. Look at Jorge's post on about the 14th.
Overwintered Bees 2010.
In the course of about a week our snow has vanished and this week we have had days in the mid-50s for temps. There have been years when the first week of April was still in the low 30s.
And with the brood of course comes the emerging young bees ready to carry out the seasons honey and pollination activities.
New bees will also help the hives survive should we get any more un-bee-friendly weather. There will be some tree pollen that comes about shortly, but it will be some time yet before the dandelions and nectar become readily available.