We've fed and watched birds for many years. The most interesting visitor I've ever seen near a feeder was at my father's house a few years ago. He lived on the edge of town and would often get interesting birds due to his proximity to fields & woods; turkeys, quail, etc. One winter, a Kestrel showed up for a few days.
(Not my pic; copied from Wikipedia)
As you can probably guess, it wasn't for the seed. But it was for the food. {S}He had learned that there were lots of fat & happy little finches and sparrows cheerfully feeding. I'll spare the fellow bird-lovers the details, but let me just say that it was pretty amazing to watch that Kestrel hunt right in my father's back yard.