Verdins (Auriparus flaviceps) are frequent visitors to hummingbird feeders here in the Sonoran Desert. These tiny birds have a real love for sweet sugar water, and I see them at my Tucson hummingbird feeders several times a day. From what I have observed, Verdins will visit just about every different style and type of hummingbird feeder.
Even though they can't hover like hummingbirds, Verdins will still happily visit perch-less hummingbird feeders that keep most other larger, nectar-loving birds like Orioles, House Finches and others away. The Verdins will briefly flutter in front of the perch-less hummingbird feeders and then grasp onto the small edges around the nectar holes.
Unfortunately, these perch-less, egg-shaped hummingbird feeders don't always keep the greedy, sugar water-spilling Gila Woodpeckers away, but unlike Verdins, woodpeckers don't like these perch-less feeders as well as other styles of hummingbird feeder. Fortunately, the tiny Verdins are light and dainty and don't make a mess with the sugar water like the larger, heavier woodpeckers.