Flightless Skeleton Goonie
From the Super Mario Wiki
Flightless Skeleton Goonies are Skeleton Goonies that do not have wings. This type of bird is similar to a Flightless Goonie. They start as a Skeleton Goonie, but they then lose their wings when stomped upon. They are, hence the name, skeletal, with two short, black legs and one hair on their head, whereas the living version has three hairs.
Tending to travel in "Flightless Flocks" of about six, they are extremely fast, and appear to be under the same zombielike properties as Dry Bones or Bony Beetle, except that when defeated, they cannot reform back into a living state. They do sometimes reappear if the player moves too far from the spot where they were defeated. They appear in Super Mario World 2: Yoshi's Island, Yoshi's Island: Super Mario Advance 3 and Yoshi's Island DS.