I've never seen this behavior before. I thought it was a turtle at first glance. It stayed in this position until I had completely passed by, them emerged an flew toward the clutch observed nearby.
Left: pink over yellow
Right: purple over yellow
Left: pink over yellow
Right: teal over purple
Left: pink over yellow
Right: teal over orange
Left: purple over purple
Right: yellow over purple
Mourning Dove (primary), Cardinal, House Sparrow