Cycle of Learning - Migratory Patterns - Card One

We're starting with a new set of cards today, diving into Enigma Emporium's Migratory Patterns. This envelope's theme is that it's our first real Institute job. We have to dig up a series of artifacts for a client, many of which we 'never dreamed to be real.' Another Institute agent has already done the work of locating them, we just have to unscramble their codes and process the items. Hmmm...

The front of the first card is a dove with letters on the top and bottom. I'm guessing Caesar because that's my default. Could be Vigenère. On the back, we have a long form message on the left, with certain letters highlighted in yellow, purple, and green, talking about ornithology and claiming to be from Audubon himself. On the right, we have a series of stamps, cancelled in Germany, above what are essentially cryptic crossword clues. Staring at it, we get most of it pretty quickly. Blair witch throws us off, then we get  "I found the holy grail". Cool. Clearly the cup of a carpenter... 

Going back to the stamps. Cancelled in Germany on March 5th. Hmmm... Apparently March 5th is Absinthe Day, Cheese Doodle Day, and St. Piran's Day. St. Piran sounds possible, given the religious theme of the stamps, but he's the patron saint of tin miners, and primarily celebrated in Cornwall... My puzzling partner looks at the stamps themselves, and finds the oldest boys' choir is in Regensburg, Germany. Strangely, I travelled there ages ago. Willing to bet that the grail is there, rather than Cornwall. So far so good, now to tackle the text. 

The text under the word 'Dove' is not, in fact, its genus or species, but should give us a clue on how to unscramble the surrounding text. As I type this, N figures it out. The letters are inverted in pairs - oculbmdiea becomes Columbidae - the genus for doves and pigeons. Our text then reads: Have arranged for local man to give you access meet him in town. His name is Alexander Edmunds.' Ok, talk to Alex in Regensburg to get the Grail? Sweet. Now, the text on the back...

Looking at the letters in color order:

• Yellow: QNPOIXLAGMK
• Purple: SPVWOZPEISIM
• Green: A J.J. Audubon  

I try brute force Caesars first, thanks to dCode for making that simple. Unsurprisingly, nada. I proceed down a rabbit hole on John James Audubon (not to be confused with the German Autobahn). While I go down that path, N thinks that maybe it's not purple, but blue, and yellow+blue = green, giving us one letter per line. It's not quite that straightforward, but Excel comes in handy. (MID, and COLUMN(INDIRECT) for those interested). 

Rather than yellow + blue (purple!) it's the middle - (yellow + blue)/2 --? Rosslyn Chapel. Which is NOT in Germany. I've been there, too. And there's a vault that they don't let anyone in to. Could it be there? And does Rosslyn Chapel mean it's not in Regensburg? Now I'm confused... Is the grail in Scotland or Germany? Also, there haven't been any Institute links that we found on the card? 

In confusion, we check the hints on Enigma Emporium's website. Apparently the stamps are wrong, or aren't ready yet - they're for the website which me must get later? The hint says we aren't to go farther at this point, so we will expect that The holy grail was found in Rosslyn Chapel, where our contact is Alexander Edmunds.

Thanks to Enigma Emporium for another fun evening :)