Hair standing on end?

I was out back this afternoon for a little bit, and this little green heron apparently felt totally safe from me in this thicket of a tree since this was as close as I could get without getting in the water (with the alligator). I know the bird was okay because a few minutes after I moved away he flew somewhere else. But is the way the top of its head looks because of being alert because of me, or is it a juvenile and that's the way juveniles look, or for some other reason?

That's how the juvies look because there adult feathers have not come in and they still have some of the down feathers

Here's what a fledgling looks like still in the nest. As Luke indicates it takes a while for the initial pin feathers to get replaced.

Thanks, Luke and Richard. Richard, I love that image.