Four out of five emperor penguin colonies in the Bellingshausen Sea, Antarctica, saw no chicks survive to fledge successfully in the spring of 2022, reports a study published in Communications Earth & Environment. The study suggests that this complete breeding failure is a direct consequence of the unprecedented loss of sea ice recorded in the region in recent years due to climate change.
Emperor penguin (Aptenodytes forsteri) colonies generally need stable ice attached to the land between April and January to ensure successful breeding and molting. Any change in the extent of the Antarctic sea ice can affect their reproduction as chicks do not develop waterproof feathers until fledging.
Peter Fretwell and colleagues used satellite images covering the period between 2018 and 2022 to monitor the presence of emperor penguins during the breeding season at five colonies in the Bellingshausen Sea in Antarctica. The colonies are known as Rothschild Island, Verdi Inlet, Smyley Island, Bryan Coast, and Pfrogner Point and range in size from around 630 pairs on Rothschild Island to around 3,500 pairs on Smyley Island.
The authors found that four colonies—Verdi Inlet, Smyley Island, Bryant Coast, and Pfrogner Point—experienced total reproductive failure and were abandoned in the period after the sea ice broke up before the start of the fledging period in December 2022. The authors indicate that it is unlikely that any chicks survived to successfully fledge at these colonies. However, satellite images suggest that chicks did fledge successfully at Rothschild Island colony. The authors note that of the five territories only the Bryant Coast colony had been identified as having experienced total breeding failure prior to 2022.
This is the first regional breeding failure of emperor penguins observed in the past 13 years in the region and among the first evidence of the direct impact of Antarctic warming on the viability of emperor penguin populations.
Penguins in western Antarctica
Penguins are heavily dependent on sea ice as part of their life cycle. In particular, they need land-fast sea ice, which is connected to a nearby coastline, to rest, molt, and hunt from. Many penguin prey species also depend on the ice for their own life cycles.
Penguins breed on the ice and raise their chicks there too. As well as providing a place to incubate their eggs, the ice also provides a platform for the chicks to stay until they have developed their waterproof feathers in a process known as fledging.
As the largest living species of its kind, emperor penguins need the ice to remain stable for an extended period of time so that their chicks can fully develop. After arriving at their breeding sites in April each year, the ice must stay intact until the chicks have fledged by January.
In recent years, however, the sea ice has become increasingly unstable. The West Antarctic Peninsula is warming at around twice the rate of the rest of the continent, putting penguin colonies in this area at particular risk of breeding failure.
Even some of the largest are not immune to these losses. Between 2016 and 2019, no chicks from the Halley Bay colony, at one point the second largest in the world, are thought to have survived after the ice broke up early. The pattern now appears to be repeating itself in the Bellingshausen Sea, located on the other side of the peninsula. Researchers looked at satellite imagery to investigate the health of the penguin colonies, with the extent of sea ice and feces marks being used to work out how the colonies were faring.
The imagery revealed that while the colonies appeared to be occupied until the end of October, the early break up of sea ice in November 2022 led to three of the colonies being abandoned during the next month. A fourth colony, Pfrogner Point, was also abandoned, though the reasons are unclear.
Only the Rothschild Island colony, where the ice is protected by the shape of the bay, is known to have bred successfully, with 820 chicks counted from helicopter surveys of the site. While it’s possible that a few chicks may have fledged from the other colonies, this hasn’t been confirmed.
As emperor penguin colonies breed all around the Antarctic coastline, the breeding failure in one region isn’t an immediate threat to the species. However, researchers have described the collapse of four previously stable colonies as ‘very concerning.’
‘The consensus view is that sea ice will not recover to its previous levels and that what we are now seeing is evidence of a continuing decline,’ Peter says. ‘This will mean that these breeding failures are an indication of what is to come for the emperor penguin.’
The uncertain future of emperor penguins
While seabirds are renowned for their ability to bounce back from population declines, the penguins’ breeding failures put pressure on a species that is already under a great deal of stress. This pressure does not appear to be letting up in 2023. The extent of sea ice around Antarctica is approximately 2.2 million square kilometers less than it should be at this time of year, which is an area about the size of Greenland.
This is already much less than at the same point in 2022, suggesting this year will also be a bad one for penguin breeding.
‘While it’s possible for penguins to recover from breeding failure in one year, 2022 came on top of an already bad year in 2021,’ Peter says. ‘Looking at the shallow winter sea ice we currently have around Antarctica, 2023 is almost certain to be worse than 2022.’
‘Though breeding failure is not happening everywhere, it’s starting to look like some areas such as the Bellingshausen Sea may become untenable in the long run for successful breeding sites.’
Because of the complexities of modeling the atmosphere, it’s not entirely sure that climate change is responsible for the recent temperature extremes in Antarctica. However, as temperatures rise, levels of sea ice are expected to decline towards the end of the century.
Dr Caroline Holmes, a polar climate scientist at the British Antarctic Survey, says, ‘Year-to-year changes in sea ice extent are linked to natural atmospheric patterns such as El Niño-Southern Oscillation, the strength of the southern hemisphere jet stream, and regional low-pressure systems.’
‘We’ll need years of targeted observations and modelling to know precisely how much the current conditions are being influenced by these phenomena and by natural ocean variability. However, the recent years of tumbling sea ice records and warming of the subsurface Southern Ocean point strongly to human-induced global warming exacerbating these extremes.’
By the end of the century, melting ice may mean that 90% of emperor penguin colonies may be on the verge of extinction. While penguins can move to more stable regions to set up new colonies, they will be left with fewer and fewer options. Ultimately, the main way to protect these animals is by taking urgent action to reduce greenhouse gas emissions. There are also calls to upgrade their conservation status at a regional and global level, which will allow plans to be put in place to protect these iconic birds.
