Hi Zipperlip, I'm not an complete expert by any stretch of the imagination. I based my ID on local experience and the birding book Field Guide to Australian Birds by Pizzey and Knight. I'll attach a photo below of the illustrations on the Nankeen Night Heron that shows their progression from juvenile plumage to mature. Another bird that looks a bit like them is the Striated Heron, it also can roost and hunt around marinas, I'll post a piccy I took a few years back on the tidal flats near our home near sunset of a Striated Heron ( also called a Mangrove Heron ). The difference between juvenile and adult plumage can make ID challenging with many birds.
