The difference between Northern and Southern Giant Petrels is small. Both species can show a wide variety of colours, from nearly all dark brown to more blotted white. The only real difference is the tip of the bill. This is yellowish-green in Southern Giants and dark red in Northern Giants. Fortunately, they have a massive bill, meaning this is often clearly visible.
Sometimes it’s easy though. If a bird is white like this, with just a few dark feathers, it has to be a Southern. Southern Giant Petrels have a, much rarer, white morph that we don’t find in Northern Giants. We don’t see this morph often, so I didn’t have excellent pictures so far. Until this year, when there was one swimming right next to my zodiac. We had to wait for another zodiac a little anyhow so I could take a bit of time to make a few pictures.