Certain species of plants have pollen, some nectar. When plants w/ abundant nectar become available, your area has a flow. The bees come back to hive w/o pollen in their baskets, flying lower to ground b/c they're weighed down w/ nectar(or water). They will begin to store nectar. It looks like a liquid in an open cell. Overtime they will cap it w/ wax.You'll see it glisten before its capped. Pollen looks like colored dots w/o a cap in a cell. Some early season plants/trees that usually indicate a flow are dandelion, black locust, white clover. I'm sure others will add to list. If your lucky, you may have multiple mini-flows, w/ larger seasonal flows.