The man spoke them in the same breath as Elfenbein, so they must be associated with Ivery's gang.
You've got to get the whole Secret Service of the Allies busy to fit a meaning to these two words.

Surely to goodness you'll find something! Remember those names don't belong to the Ivery part, but to the big game behind all the different disguises ...

Then there's the talk about the Wild Birds and the Cage Birds.

I haven't a guess at what it means.
But it refers to some infernal gang, and among your piles of records there must be some clue.

You set the intelligence of two hemispheres busy on the job.