My USA instruction manual for Donkey Kong Country 2 says this about Animal Barrels:

"Barrels marked with an animal friend's picture will transform Diddy or Dixie into the animal if they jump in. If you jump into a Barrel that shows a picture of the animal that you are already transformed into, you will gain an extra hit as that animal."

The last sentence is not true. I have confirmed that the Animal Barrel does not extra hits.

I declared (in some SMWcentral forum thread) that I wanted to disassemble Donkey Kong Country 2, but I have not started, because I am too busy with my disassembly of Mario Paint. So, I have not found any 65816 machine code for Animal Barrels.

Instead, I played a clean copy of Donkey Kong Country 2 and entered an Animal Barrel of Squawks after my player character already transformed into Squawks, the flying green parrot who spits eggs.

In DKC2, the Star Barrel is the midway point of a stage. The stage titled Screech's Sprint has a Star Barrel near an Animal Barrel of Squawks. So my player character jumped into the Animal Barrel, then broke the Star Barrel as Squawks, then died. My player character restarted the stage from the Star Barrel, while already transformed into Squawks. The Animal Barrel reappeared because I restarted the stage. So as Squawks, my player character flew into the Animal Barrel, but failed to gain an extra hit as Squawks. For an extra hit, I would need to instead break the nearby DK Barrel.

I have no screenshots, because I used a real SNES (not an emulator that makes screenshots).

So, if I want Squawks to take an extra hit without losing a life, then I must fly into a DK Barrel (not into another Animal Barrel of Squawks).