Spring has come to the 42N latitude. That means the Mississippi River is open to boat traffic, which also means waterway birds are back in numbers. Yesterday a single seagull glided over the empty lock enclosure at Lock & Dam 11, Dubuque, Iowa. Those of you in the know already guessed that the first four words of this blog posting title are from Paul McCartney's underrated classic song, Single Pigeon. Watch this animated video.