From calligrafiti: "...the birds are aggressively mugging my bird feeder..."

Yep. Sounds like birds to me. And, if my memories are correct, each other as well, flittering and squawking and pecking and displaying the worst violent inclinations of the species, like suburban moms in the mall on Christmas Eve.

Nature is not kind and gentle. Watch a cheetah. Look at a thunderstorm. When male birds sing in defense of their territories, understand it as an opera in a foreign language, with a translation running something like this: "Yo momma sucked my cock this morning, and if you come over here to give me any shit about it, I'm gonna kick your punk ass."

Chickens are vicious cannibals, by the way. The only thing I've come across that are more cruel than chickens are middle-school girls.