It's well known for his weird attitudes when caught, or near the nest, but this one was just leaning to the left, for a minute or so. It could be mimicry, trying to look like a piece of wood, as we can hear alarm calls ... ?
https://www.youtube.com/watch?v=NE2dJcDs3m0
https://www.youtube.com/watch?v=NE2dJcDs3m0