Another metric the bees use well is the gain or loss per trip. IE If it take 40 calories to go on a mission to collect 35 calories of nectar they will not do it. If they use 35 calories to go on a trip to collect 50 calories then it is worth the trip. They normally will go 2-3 miles, 5 miles in a dearth. However the farther they go the better the nectar needs to be. They do not make trips with no gains. with parks and such there is also trees some have nectar or pollen.