World's largest penguin colony hit by 'alarming' decline in numbers

Almost two‑thirds of the chinstrap penguin nests on Zavodovski Island have disappeared since 2011, aerial surveys by the British Antarctic Survey (BAS) indicate. The island, part of the South Sandwich Islands archipelago and a UK overseas territory, once hosted the world’s largest penguin colony—an estimated 600 000 chinstrap and 90 000 macaroni penguins in 2011. Between 2011 and 2025 the number of occupied chinstrap nests fell by 63 %, according to BAS research that combined drone imagery, aerial photography and tracking devices fitted to 20 birds. Professor Norman Ratcliffe, who led the study, linked the decline to climate‑driven changes in food availability. “With waters warming, the krill [that the chinstrap penguins eat] have moved southwards,” he said. “Sea‑ice cover to the south and a lack of suitable islands for nesting prevents chinstraps from pursuing the food.” The researchers described the loss as “alarming,” noting that rising sea temperatures and shifting krill distribution are the primary pressures on the chinstrap population, which relies on a specialist diet and cooler waters. In contrast, macaroni penguins on the same island have increased dramatically. Scientists attribute this to their broader, more flexible diet. Tracking data showed macaronis foraging in warmer waters to the northeast of Zavodovski, where they supplement their intake with fish and other crustaceans. Dr Ratcliffe remarked, “This shift was biggest alteration in community composition ever observed at a single location in Antarctica.” He added, “Our data shows that the cold‑adapted Antarctic chinstrap species are no longer thriving beside their sub‑Antarctic neighbours.” He concluded, “It is further evidence of how rapid warming in the Antarctic is impacting isolated and delicate ecosystems.” The team also examined other potential threats. Penguins nest in the shadow of the active volcano Mount Curry—also known as Mount Asphyxsia—where downwind sites bear names such as Stench Point, Noxious Bluff and Asphyxia Plain due to volcanic fumes. Ratcliffe told BBC News, “When you add all the penguin guano on top of that, and you truly do have one of the smelliest places in the world.” He continued, “It’s like a penguin Mordor.” Although Mount Curry’s last major eruption occurred in 2016, the penguin decline has been steady since 2011, indicating other factors are at play. Competition for krill—possibly from migrating humpback whales—was considered, but researchers concluded that a fundamental, climate‑driven shift in marine nutrient supplies is the main driver. With the chinstrap colony diminished, the title of world’s largest penguin colony now belongs to a site more than 5 000 km away at Cape Adare in the Ross Sea. The findings are published in the journal Current Biology (https://www.cell.com/current-biology/fulltext/S0960-9822(26)01186-3).