There is a belief that bees start preparing for the swarming event well before the old queen departs, like monthes before--substaincial quanities of workers remain in the hive loafing inside, filled with honey--being inactive the consumption rate would be quite low, coupled with the steadyily increasing worker population, over crowding would stimulate the actual queen cell rearing. as the first queen cells capped over the old queen departs--with all the loafers in the colony with represents about 40% - 60% of the adult population. The concept makes sense. But also means that the bees were making descions well in advance of the " swarming impulse "
Perhaps not so much a impulse as thought?