# A bird-brained cipher

Today my partner, an avid ornithologist who I swear spends his whole day looking at codes and tables online, left me this cryptic clue when I asked where he had been all day. He complained about a change from 6th to 7th edition of some checklist and how he stuck with 6th edition because he liked it better, but I never understand what he's on about. He can be a bit of a birdbrain, so hopefully one of you can help me figure out what he's talking about!

Where has he been?

4540 (2) 0431 (2) 4610 (2) 8506 (2) 3980 (2) 5332 (1)

• If this goes into the direction I think it does, rot13(ner lbh fher gur fvkgu rqvgvba vf serryl ninvynoyr bayvar ba aba-fxrgpul jrofvgrf? V pna bayl frrz gb svaq gur arjrfg irefvbaf bs cbffvoyr pnaqvqngr yvfgf.) Commented Sep 12, 2020 at 12:00
• @LukasRotter The sixth edition numerical table was available freely on a government website, so I figured it would be okay to use as a reference for the puzzle. Commented Sep 12, 2020 at 21:37

(not surprisingly) AT THE AVIARY

Reasoning:

There are several references to birding and birding checklists, and a quick Google search reveals two main birding checklists: the AOU (American Ornithological Union) and ABA (American Birding Association) versions. The AOU (now AOS, American Ornithological Society) version went through a somewhat controversial migration from version 6 to version 7, which included dropping numerical codes for bird species from version 6. With some digging, there is an online reference which gives a list of these numbers. Looking up the numbers in the given cipher yields

4540 = Ash-Throated Flycatcher
0431 = Thayer's Gull
4610 = Eastern Wood-Pewee
8506 = Victoria Penguin
3980 = Arizona Woodpecker
5332 = Yellow-fronted canary

To extract the message however, you do not need the common names of the birds, but rather the four-letter alpha codes associated with each:

4540 = ATFL
0431 = THGU
4610 = EAWP
8506 = VIPE
3980 = ARWO
5332 = YFCA

Finally, the numbers in parentheses behind each code indicate the number of letters to extract from each code, yielding the answer AT THE AVIARY.

• +1 for 'migration' ;-) (and the solve of course!)
– Stiv
Commented Sep 12, 2020 at 12:10
• This is it, excellent job! :) Commented Sep 12, 2020 at 21:36