Keep It Clean Achievement in Halo: The Master Chief Collection

This achievement is very straightforward and can be earned on any difficulty.

Throughout the Winter Contingency mission, there are several bird-like creatures (Moa) roaming around the area (ie, two in the beginning before making your way into a small structure, nearly five shortly after getting into the mission's first vehicle, etc.). Moa are rather weak and can be killed easily, but they are also very fast and will flee if you get too close. With this in mind, simply kill seven any way you see fit over the course of this mission and the achievement will unlock.