Bats siphoning my hummingbird feeder?

For the last 2 weeks I fill the Hummingbird Feeder in the morning and it's still full in evening when I go to bed. The next morning it's empty!!! Nothing is spilled or splashed on the deck or window.

If it was a raccoon or other night wanderer, we would hear the ruckus and see that the feeder had been tampered with.

My only guess is that the bats are siphoning it out during the night. I've been told that only SouthWest bats are nectar lovers and drain the feeders in Arizona near the Mexican border, but what else could do this to my feeder?

Thanks for any suggestions. As of tonight, I brought in the feeder at night and will put it back out tomorrow morning.

That is correct - bats in your area are all flying insect eaters, and there aren't as many bats in your area as there used to be (White Nose Syndrome).
Nothing spilled? I know that larger birds perch on mine and tip it. How about rats or mice? They might be small enough to drink out of it, especially if their weight tipped it towards them.