If you have been feeding through the winter or early spring, keep doing it; changing weather can force the bees to stay in the hive limiting their ability to forage. If your hive is weak, you may need to give a pollen substitute to ensure brood growth. The warm weather is bringing out the early blooming plants and the bees are now desperately seeking pollen for the brood. Dandelions, willows, fruit trees, and some berries are now in bloom and are the major source of pollen for the first part of the season.
Now is the first real month of work for the year. You will need to check your hives on the first warm day for eggs, signs of diseases, and to reverse the brood supers. If the colony is strong and is already covering much of both boxes, there is no need to reverse the boxes. If you find a strong colony, consider splitting as the weather warms. Clean the bottom board either way.
Estimate how strong the colony is; if weak, consider combining with another colony. Check for brood at several stages of development; the chance of dwindling (where old bees die off faster than new bees emerge) can happen if temperatures, weather, and food sources are less than ideal.
When you are looking in the hive, check for mites or signs of disease. If you find signs of disease or parasites, take immediate steps to treat and prevent the problem from becoming epidemic. Towards the end of the month, begin looking for colony growth or swarm cells. Add supers if needed to prevent swarming.
For those of you starting new this year, make sure all of your equipment is assembled and painted. By now, you should have at least one deep brood box and 10 frames ready, along with a bottom board, inner cover, cover, and feeding mechanism for when packages arrive. You must have a place for those bees when they arrive.