Every December, the Fiordland crested penguins, Eudyptes pachyrhynchus, which live on the South Island of New Zealand, disappear. Researchers assumed they swam off the coast of the island on extended feeding trips. But no one had ever followed them. The New Zealand Herald reports that researchers did recently track the birds, finding something incredible; they make an epic 4,000-mile round trip south, in less than two and a half months.
To study the incredible journey, zoologists from Otago University tagged 20 of the penguins with satellite trackers. Then they sat dumbfounded as the seabirds swam farther and farther south. “My first reaction was there's something wrong with the data,” project director Thomas Mattern says in a press release. “Then I was just puzzled, I was completely flabbergasted—where are they going, when will they stop?”
The birds, also known as Tawaki, stopped about halfway to Antarctica in a feeding area where warm and cold waters collide. The research appears in the journal PLoS One.
The big question is why the birds feel the need to go so far out to sea. The Herald reports that the reason for the feeding frenzy is well understood. After raising their chicks, the birds undergo their annual molt, when they grow a new set of feathers. It’s a three week process where they have to sit around and they aren’t able to hunt for food. So in preparation, they need to pack on the fat and head off to gorge. Raising chicks and growing a new cloak of feathers are both energy intensive, so it would make sense that the animals try to conserve as much energy as possible. But they don’t.
Even stranger, at the same time they set out on their epic adventure, the fishing around their island home gets really good and there’s a veritable seafood buffet they could use to beef up. “The conditions closer to the New Zealand mainland are pretty good,” Mattern tells George Dvorsky at Gizmodo. “There are no obvious reasons why Tawaki would have to travel as far as they did—there is no logical explanation for it.”
The culprit may be instinct. The Tawaki are just one of several crested penguin species in the Southern Ocean, though the other members live farther south. It’s possible that the instinct to swim to the far-off feeding ground is a leftover urge from an ancestral crested penguin species that has never been corrected.
The ocean voyage also casts some light on the range of the sleek swimmers. Zoologists once believed the species may have been more widespread in New Zealand and were eventually pushed into the southern edge of the South Island by human hunting. But if they make this epic journey annually, it would make sense that they primarily live in their current range, “[C]onsidering that breeding further north would add another few thousand kilometers to the penguins’ journey, it appears that tawaki breed exactly where their migratory behavior allows them to,” Mattern tells the Herald.
It’s also possible that this swim-off, which was recorded in 2016, was just a one time blip. Dvorsky reports that the data was also incomplete. Though researchers tagged 17 penguins, only nine of the data loggers lasted to the halfway point, and only five survived the journey there and back. And of course the data is only from a single year. That’s why the crew currently has 48 penguins tagged hoping to collect data from the birds over the course of a year.
Who knows, maybe they take more than one marathon swim.