A grounded iceberg cut off one of Antarctica’s largest emperor penguin colonies from its feeding grounds in 2025, and a new study says the disruption likely triggered one of the worst breeding failures ever recorded for the species.
The Numbers
Researchers from the Korea Polar Research Institute (KOPRI) counted just 6,658 live chicks at the Coulman Island colony in the Ross Sea during aerial surveys in November and December 2025 — a drop of roughly 69% compared to both the 2024 count and the 2017–2024 average. The colony’s population had stood at around 21,000 the previous year.
How the Iceberg Trapped the Colony
The iceberg, measuring about 13.9 kilometers (8.6 miles) long and 4 kilometers (2.5 miles) wide, broke off from the Nansen Ice Shelf in March 2025. It drifted north and grounded just 3–5 kilometers from the Coulman Island colony by late July — right as the penguins’ hatching season began — and stayed lodged there until January 2026.
Using field observations and aerial imagery, the research team, led by Dr. Jeong-Hoon Kim, found that the iceberg’s southern wall rose more than 20 meters high, forming a wall the penguins had to travel around. This pushed the average foraging trip from about 9.3 kilometers in 2024 to roughly 14.9 kilometers in 2025 — an extra 5.6 kilometers each way for adults already making repeated trips to feed their chicks.
Why the Extra Distance Mattered
Emperor penguins depend on frequent trips between the colony and open water to keep their chicks fed between June and January. The longer, harder journey around the iceberg likely meant fewer feeding trips per adult, leaving many chicks without enough food to survive, researchers say.
“The surviving 30% of chicks were likely fed by mothers who managed to find an alternative route,” said lead researcher Dr. Jeong-Hoon Kim.
Why It Matters
Emperor penguin breeding failures have mostly been linked to large-scale sea-ice loss in the past. Studies on colonies in the Bellingshausen and Weddell Sea regions, for instance, have documented population declines tied to shrinking ice over multiple years. Coulman Island’s case is different: it points to a single, localized event — a grounded iceberg — as the trigger, rather than a broader climate trend.
That distinction matters for how scientists monitor emperor penguin populations going forward. It suggests colonies considered relatively stable, like those in the Ross Sea, can still face sudden, sharp disruptions from physical obstacles alone, not just from warming oceans or thinning ice. Researchers say this makes iceberg activity an important factor to track alongside sea-ice conditions when assessing risks to the species, whose global population is already projected to decline in the coming decades.
What Happens Next
Kim’s team says the colony’s recovery now depends on whether the ice clears in time for the next breeding season. If the iceberg breaks free before the season starts, the colony could rebound; if it stays lodged in place for years, the penguins may eventually be forced to relocate to a new breeding site.
The researchers caution that their findings cover a single breeding season, and more monitoring is needed to understand how often grounded icebergs disrupt penguin colonies elsewhere in Antarctica.
