From the Super Mario Wiki
Crowber is a crow-like enemy first seen in the game New Super Mario Bros.. These enemies tend to appear in the last levels of the game where they attack Mario or any other potential victim with rather fast moves. The name Crowber appears to be a pun from "crowbar", a tool used to remove nails.
New Super Mario Bros.
Crowbers are only seen in World 8-1, where they swoop down to attack Mario. As progress is made throughout the level, more will appear and chase after the player. Crowbers attack quickly, making it somewhat difficult for the player to defeat them.
New Super Mario Bros. Wii
Crowbers also reappear in the game New Super Mario Bros. Wii. This time, they have a purple plumage and a lighter beak and legs, and appeared in World 7-Ghost House and World 8-5. They attack in the same manner as they did in New Super Mario Bros..
New Super Mario Bros. 2
Crowbers reappear in the Nintendo 3DS game, New Super Mario Bros. 2. They appear in World Mushroom-, World 6-4 and in the first level of the Impossible Pack. They maintain their appearance from New Super Mario Bros. Wii.