My guess is the birds leave because they have broken up into nesting pairs. Their breeding territory is a few acres per pair so they are a little scarce. Next when the young have fledged the parents bring the young back into your yard. Regarding the drinking, given a choice they will go for fruit before nectar.

Hope this helps. John

NOW

Lets talk about this problem of birds disappearing from are area in the Spring for weeks on end.

I have run into this for the last thirty years, all the way back to when I was operating a wild bird store in Fairport NY. For some reason it seems like all of a sudden the feeding stations are empty and there are no birds around. I have spent hours and hours and even more hours trying to find out why this happens. So far no answer (I'm anxiously waiting!)

This much I can tell you "It ends as fast as it begins." Takes four to six weeks, but I have never know the birds not to come back just as though nothing ever happened.

John