The Birdy stem mounting is an Ahead type of stem but inverted: the fork is like the stem of a regular Ahead, the stem is like the fork of a regular Ahead with a tube inserted in the fork, the fork being tightened around the stem tube. And has with any Ahead, there is a bold to adjust the bearing play which on the Birdy is between the fork legs that can be seen on the picture below (torx head bold):



The two bold on the picture below are for tightening the fork around the stem tube (they must be untightened before adjusting the bearing play with the bold above and then retightened).