Quick note for LabRat: The "white stuff" in a hummer's nest is SPIDER WEBS
It's a really soft and strong building material, they almost sculpt with it. The little critters eat the spiders too (small ones, obviously) as a large part of their protein. Sometimes they weave the down from milkweed pods and similar soft plant fibers, but mostly they build up a cup with lichens and the webs. What's really cute is when they hang the nest from a twig like a big swing. Hummers are fascinating to watch, we have 9 feeders at our house and it's like sitting on the runway at a busy airport if you are outside around dusk!