King penguins on Possession Island are breeding earlier due to rising temperatures, leading to higher chick survival rates. While this has boosted chick numbers from 44 percent in 2000 to 62 percent in 2023, researchers warn that shifting food sources could threaten the population in the future. The changes highlight rapid environmental shifts in the Southern Ocean.
King penguins (Aptenodytes patagonicus) on Possession Island, a French territory between Antarctica and Madagascar, have adapted to warmer conditions by starting their breeding season about 19 days earlier in 2023 compared to 2000. This adjustment, linked to higher sea surface temperatures and lower plankton levels indicating abundant lanternfish, allows chicks more time to feed and build fat reserves before winter, reducing starvation risks.
Research led by Gaël Bardon at the Monaco Scientific Center shows chick survival has risen to 62 percent on average, up from 44 percent two decades ago. Pairs tend a single egg during the austral summer, with chicks hatching after roughly two months. Parents forage hundreds of kilometers south at the polar front, where nutrient mixing supports plankton and small fish like lanternfish, which they deliver to the young.
Bardon notes, “With king penguins, we can see that there are super-fast changes in the Southern Ocean that are good for them for the moment, but for the long term, we don’t really know.” Although the local population remains at carrying capacity, surplus birds may be expanding colonies elsewhere.
Team member Céline Le Bohec describes the breeding shift—faster than in most polar species—as an “alarm call” for environmental changes. In warmer periods, the polar front has moved southward, forcing longer foraging trips and past population drops on the island. Without southern islands to relocate to, extended ranges could lead to declines if the front keeps retreating, as a prior study suggested.
Le Bohec warns, “This fast change, which increases the window for the breeding cycle, is positive, but once the food availability at the polar front will be… too far away from the colony, it will collapse. You will reach a tipping point.”
Other experts offer nuance. Lewis Halsey from the University of Roehampton highlights the penguins' flexibility, including eating squid nearer the island, predicting shrinkage but no collapse. Tom Hart of Oxford Brookes University calls it “a good news story” and a “rare win” amid declines in other penguin species.
The findings appear in Science Advances (DOI: 10.1126/sciadv.aea6342).