During these first warm and sunny days of spring, the bees literally climb over each other to get in and out of their tiny entrance. You’ve got the urge to remove the entire entrance reducer so they have plenty of room to move about. But be careful.
Pollen is usually in good supply before nectar and, until the nectar starts flowing, your bees are collecting mostly pollen—and craving a source of carbohydrates. If the entrance reducers are removed too soon, stronger colonies may take the opportunity to rob the weaker colonies of any honey they have left. If you see a great crowd of airborne bees in front of a weak hive, this may be what is happening.
So until nectar is plentiful, keep the entrance reducers on the weaker hives, and fully open only those you know to be strong and populous. After nectar becomes more available, the weaker colonies will expand and soon be able to defend their hives. At that point, you can enlarge their entrances or remove the reducers altogether.