Antarctic Birds: Snow Petrel

One of my favourite tubenoses is the Snow Petrel. With their completely white plumage and black bill, eyes and beak, they look a bit like angels. They are pagophilic, which means they are ice-loving and indeed, we see them mostly close to sea ice or large bergs. They have a circumpolar distribution and can also be seen on some subantarctic islands, like South Georgia (Drygalski fjord is a famous spot down there).

Snow Petrel in Drygalski Fjord on South Georgia.
Snow Petrel – they look like angels

They are one of the southernmost breeding birds on Earth. They breed on cliffs along the Antarctic coast, but also on nunataks, mountain tops sticking out of the Antarctic ice cap, sometimes as much as 250km inland. Here they take turns incubating their single egg for around 40 days and raise the chick together in another 50 days.

Two Snow Petrels calling at each other
Snow Petrel on the nest

They use the same colonies over and over again, as was shown by a Swedish study from the 1990s. Just like other tubenoses, they make a kind of stomach oil which they spit out to anything that comes close to their nest. This oil stinks and is difficult to get rid of, so this is an excellent way to repel predators. So after a year, there is a thin layer of this stomach oil around the nest, which gets thicker over the years. When those scientists carbon-dated the oldest fossilised stomach oil of two colonies, the results were quite stunning. From a colony which was at a fairly low altitude, the oldest fossilised stomach oil was well over 3000 years old. The colony, which was higher up on the mountain even had stomach oil of over 37.000 years old. This means that the colony was already in use during the last glacial maximum!

Snow Petrel near the sea ice
Snow Petrel in the stormy Southern Ocean

Snow Petrels feed on a variety of plankton and fish, which they mainly catch from the surface, but they can make shallow dives as well. One time I got lucky while my zodiac was stuck in the pack ice in the Weddell Sea and a Snow Petrel landed right in front of it and grabbed a fish. As the fish was a bit too big to swallow at once, he had to bite it in two before he could eat it. As all of this happened only a few meters away from my zodiac, we had front row seats for this spectacle.

Snow Petrel eating an ice-fish

There are two subspecies of the Snow Petrel, the Greater and the Lesser Snow Petrel. The Lesser Snow Petrel is by far the more common one of the two and by far the more likely candidate to see on most trips to Antarctica. It’s not easy to separate the two, especially when you don’t see them together. There is a reasonable size difference, but this is difficult to see when seen alone and the Greater Snow Petrel is a bit bulkier as the Lesser, which, with experience, can be used to separate the two. What complicates the matter is that the two subspecies frequently hybridise, making it even more difficult to tell them apart. On the Balleny Islands, just north of the Ross Sea, there are some pure Greater Snow Petrel colonies and the only time I’m sure I saw Greater Snow Petrels was while passing those islands on my way to the Ross Sea.

Lesser Snow Petrel
Greater Snow Petrel – a bit bulkier, thick-necked as the Lesser.

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