What is the origin of the Aztec spirit bird?

Thanks for writing to us and for your encouraging words - always much appreciated.
We think this all stems from the pioneering work, nearly eighty years ago, by the Mexican illustrator and designer Jorge Enciso, who back in 1947 published a now classic work Sellos del antiguo México (‘Stamps from Ancient Mexico’), which was reproduced in a popular Dover Publications edition in 1953. He carefully researched and illustrated many hundreds of pre-Hispanic stamp designs in museums and private collections. His illustrations are constantly reproduced today and have been copied and imitated multiple times. We reproduce here the page from his original book, which he captions ‘Representations of fantastic [ie unidentified] birds used as decorative motifs on flat stamps’. The only information he includes on the first one (our main image above) is that it comes ‘from Mexico City’.
Enciso writes ‘Stamps could be applied in two different ways: to print in colour or to stamp in relief. Printing could be done on skin, as a sign of distinction or an identification on clothing, paper, etc. or as an adornment symbolic in rites and customs... Stamps were also used for decorating food and pliable objects.’

Page 99 of Jorge Enciso’s book ‘Sellos del antiguo México’; the first illustration, top left, appears to have gone viral as an ‘Aztec spirit bird’