Names are always confusing. In German, "Schwarzkopfmöwe" (lit. black-headed gull) is "Mediterranean gull" in English. Your "Black-Headed Gull" is "Lachmöwe" in German (lit. laughing gull) and your "Laughing Gull" is an "Aztekenmöwe" in German. Not sure why it has to be so confusing!
For common birds, you can see why people didn't want to give up their long established local name for birds even as scientists tried to regularise them. Thus, Latin names :)
For the real madness compare UK & American bird names and the actual species named in taxonomies.