Interesting House Finch Behavior

Not all of the birds which use our nectar feeders are hummingbirds. Over the last year I have noticed other birds that pay these feeders visits. Some, like the chickadees, enjoy taking a drink of water from the ant moat. Wrens appear to probe for insects that are trapped inside. But the House Finches, they mystify me. No photo I took gives me a good idea what draws them there, but many photos show one. They aren't obvious insect eaters, they typically drink at bird baths, and there's no way they can draw nectar with their beakage. Can it be a stopping and resting behavior? or am I missing something? I must keep watching and hoping that one day I'll crack this little mystery.