Gentoo Penguins are breeding earlier - and dodging deadly heat
A long-running camera study in Argentina has found that Gentoo Penguin chicks are highly vulnerable to hot weather, but an earlier breeding season is currently helping them avoid some of the most dangerous summer heat.
Climate change is usually bad news for cold-adapted seabirds, but a new study of Gentoo Penguins at Martillo Island, in Tierra del Fuego, has found a rare and temporary upside: chicks are now fledging earlier and avoiding some of the hottest days of summer.
The study, published in PLOS One, used time-lapse camera images taken between 2013 and 2024 at one of the northernmost Gentoo Penguin colonies. Researchers found that the birds have advanced their breeding season by around two days per year, meaning chicks are leaving the colony sooner than they did a decade ago.
That shift matters because Gentoo Penguin chicks are poorly equipped to cope with heat. Their down helps protect them from cold, but it also makes it harder for them to lose excess body heat. At Martillo Island, chicks were seen panting when temperatures reached 18°C, while at 20°C and above many moved away from the nesting area, apparently seeking cooler conditions at the beach or under nearby bushes.
The danger was made starkly clear during a three-day heatwave in January 2015. Temperatures at the colony reached 24°C and five of 32 chicks died within 45 minutes. The deaths were witnessed in the field and later confirmed from the time-lapse camera images. The researchers could not prove heat was the direct cause because the carcasses were too decomposed for detailed examination, but they ruled out obvious causes such as starvation, predation or external injury.
Over the study period, the colony itself continued to grow, with nest numbers increasing by an average of 12.2% per year and chick numbers by 12.7% per year between 2013 and 2023. However, the main finding was not simply that the colony was growing, but that the timing of breeding was changing.
By 2023, the end of the post-guard period - the stage when chicks are no longer fully protected by their parents but are not yet ready to go to sea - had moved forward by 23 days compared with 2013. In recent seasons, this has allowed chicks to avoid more of the hot weather that arrives later in the summer.
The researchers describe this as a rare example of a climate-related shift in breeding timing having a short-term benefit. In many species, earlier breeding can create problems if chicks hatch at the wrong time in relation to food supply. At Martillo Island, however, the earlier schedule has not yet caused an obvious mismatch, and chick productivity has remained broadly stable.
But the study also warns against seeing this as simple good news. The authors make clear that this advantage may only last while the birds can continue to stay ahead of the hottest part of the season. If heatwaves become more frequent, more intense or last longer, breeding earlier may no longer be enough to protect chicks.
For now, the Martillo Island Gentoos appear to be showing the flexibility for which the species is well known. Their ability to adjust the timing of breeding is helping chicks avoid some dangerous hot days on land. But the 2015 chick deaths show how narrow the margin can be for young penguins at the warm edge of the species’ range.
The study concludes that Gentoo Penguin chicks are highly susceptible to high temperatures during the post-guard period. Temperatures of 18°C and above trigger heat-stress behaviour, while 20°C appears to be a critical threshold at which chicks begin moving away from the colony to cool down. Sustained temperatures of 24°C were consistent with lethal heat stress.
In the short term, earlier breeding is helping this colony dodge some of the worst summer heat. In the longer term, the researchers warn, that flexibility may not be enough if warming continues.
May 2026
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