What's She Doing?
Is she "smacking her lips" in anticipation" of the nectar she'll be lapping with that long tongue? Is she somehow picking up extremely tiny insects or testing the air around the feeder for microscopic droplets—sort of "smelling the air" around her? We can't know for sure. More photos/video of hummers as they approach feeders, rather than while they're feeding at them, could help us learn how common this interesting behavior is!
"This female Anna's has a habit of sticking out her tongue when she approaches a feeder, but she always pulls it back before she begins to drink."
John Doerper in Bellingham, Washington (October 10, 2013)