From the Super Mario Wiki
Flightless Goonies are Goonies that lost their wings. They appear in Super Mario World 2: Yoshi's Island, Yoshi's Island: Super Mario Advance 3 and Yoshi's Island DS. If Yoshi swallows a Goonie and then spits it out, it will become a wingless Flightless Goonie. Different from other enemies, stomping on them will not send Yoshi into the air. Later, in both games, Flightless Skeleton Goonies appear. A Flightless Goonie's primary method of attack is running into Yoshi. They usually appear in packs.