When was DJ wearing an eagle mask?

Ooof, it's been a while, but doesn't he spy on the gathering and see?

Well, he goes to the conclave at the swamp, but I don't remember DJ wearing an eagle mask or even any kind of mask there.

Gabriel calls DJ "Brother Eagle" there, and that's the hint for the puzzle later in the game where you have to know that DJ is "Brother Eagle." But how did Gabriel know that DJ was Brother Eagle when they were at the swamp? I don't remember ever seeing DJ wear any mask.

Dr. John was probably wearing a eagle's beak over his nose, or something, and we don't see it.

Dr. John did address Gabriel as "Brother Crocodile," so that's probably how Gabriel knew to address a celebrant as "Brother/Sister (insert name of animal mask here)".

DJ had an eagle tattoo on his back - this, and the feathers that adorned his wrists, ankles and neck clued Gabriel in to deducing that DJ's "animal" motif was an eagle.

The novelization of GK1 provides this explanation. With the game, it's expected the player should be able to come to the same conclusion themselves, as it is, stated in an earlier post, a hint to another puzzle late in the game. I don't blame people for not noticing this at first because he lacks the feathers in the game - he's only got the tattoo, if I can remember. In the book, he's decked-out a bit more with his costume (of sorts.)