The last photo helped me understand why they stand with their bills skyward. They have stereo vision looking downward, so with their bill in the air, they can look forward. Plus, it's good camouflage. It was actually a bit too close - I had to back up to fit it in the camera frame. There were 5-6 people there. The Bitterns were only about 10 yards off the main path.
It wasn't especially early either - like 9-10am or so. Never had an encounter like this previously. I think it's just a matter of luck.
I'm curious to learn how common it is for Bitterns to be in the open, and why they might be.
I took a friend to Fernridge yesterday afternoon and as we walked west on the Royal path we saw a bird on the side of the path just past the turn to the platform. It appeared to be a Bittern in typical vertical head pose.
Not convinced that light and angle might not be making a GBH into a Bittern, we crept forward as slowly as possible. It was clearly a Bittern and it did eventually fly, fully confirming for me. I was initially more skeptical than my companion, because I've never encountered a Bittern in the open like that.