Additional thing to consider: how far do they have to travel to reach a prime source of nectar. As Van (I think) said in response to another question, no to be a wise guy, but it's like asking how long is a piece of string. Too many variables to consider to come up with an answer. Good question to ponder when finding an answer really is not that important, but I guess "one heck of a lot." is about the best I can come up with.