King penguins dive significantly deeper in the winter Free

Even amongst penguins, there's a pecking order. Emperor penguins are at the pinnacle, capable of dives exceeding 550 m, with smaller king penguins coming in a reasonable second at 343 m. However, Maëlle Oberlin, from the Université de Strasbourg, France, and colleagues explain that many of the recordings that measured king penguin dives were made during the summer, when the aquatic birds embark on relatively brief foraging trips (1–2 weeks) from Possession Island in the Southern Indian Ocean (46°S) while rearing their chicks. But as the sun leaves the sky and the king penguins’ favourite morsels – lantern fish – probably descend deeper in the ocean, the birds leave their chicks in creches and venture as far as the Antarctic pack ice, 1600 km further south, on months-long odysseys in search of food. ‘King penguins adjust their foraging behaviour during winter’, says Oberlin, explaining that scientists had recorded king penguins in the 1990s diving more deeply in winter than during the summer. However, no one had looked in more detail at this apparent seasonal difference, so she, Charles-André Bost (Centre d'Etudes Biologiques de Chizé, France), Yves Handrich and Manfred Enstipp (Université de Strasbourg) decided to learn more.

Robin Dardel (Université de Strasbourg) headed south to Possession Island, securing motion- and depth-sensing GPS trackers to the backs of nine king penguins (male and female) as they embarked in late April 2023 (during the southern autumn), hoping that as many as possible would return to their home beach toward the end of the southern winter. Fortunately, eight of the original nine penguins did within 4 months, although one of the trackers failed, leaving Handrich and Oberlin with seven to investigate.

Separating out the shallow (less than 50 m) dives, Oberlin was left with 18,821 deep dives to analyse. Remarkably, 326 dives went beyond the previous 343 m dive record, and when Oberlin calculated how long the penguins remained submerged, 37 dives were longer than the previous 9.2 min record. Looking closer, Oberlin realised that almost all of the penguins were going deeper, but one – humorously named Jacques Mayol after the legendary French free diver – was a true Olympian, descending more than 400 m on 12 occasions and once reaching 424.5 m, which is respectable – even for champion emperor penguins – and 81.5 m (24%) further than king penguins had ever been seen to go before. And when Oberlin investigated how long the king penguins remained submerged, four of the birds exceeded the previous record (9.2 min), with Jacques Mayol setting a new record of 10 min diving in the ∼3000 m water off the Crozet Plateau. However, when Oberlin compared the amount of time the penguins spent at the bottom of the dive relative to the entire dive cycle duration (including the period spent at the surface after a dive) – known as the dive efficiency – the super-deep dives were much less efficient (14%) than the extremely long dives (23%).

But how can king penguins reach greater depths in the winter than in the summer? The team suspects that it could have something to do with the birds’ ability to hold their breath. In the winter, the lantern fish, upon which the penguins dine, might move deeper and farther south, forcing the birds to voyage further. This in turn may alter the amount of fat they carry and lower their body temperature, enabling them to remain submerged for longer and dive more deeply during winter, compared with the shallower dives they perform in the summer.