Recently, I found a video from Nick Tumminello that puts a new twist on the birddog.
This is a great glute activation exercise. Like we talked about before the whole concept of the birddog is to stabilize the spine while the joints around it are mobilized. By placing flexing the opposite hip you put the pelvis into posterior tilt eliminating lumbar spine compensation and forcing the glutes to do the work.
An erercise like this fits well into the warmup to get the glutes firing before other lower body activities.