Shrinking sea ice makes it harder for seabirds to find food

Antarctica’s rapidly shrinking sea ice could have a significant impact on the food supply of seabirds that breed far from the continent, according to new research. 

Most of the world’s albatrosses and their relatives, the petrels, breed on islands in the Southern Ocean surrounding Antarctica. These seabirds rely on the nutrient-rich waters affected by the seasonal sea ice for feeding.

Monitoring the movement of seabirds

A study led by Durham University in collaboration with the British Antarctic Survey (BAS) used satellite tracking technology to monitor the movements of these birds. 

The researchers discovered that albatrosses and petrels travel vast distances to reach areas affected by sea ice, known as the Antarctic seasonal sea ice zone. 

This is where they either feed in the nutrient-dense waters left behind after the ice melts each summer or, in the case of southern giant petrels, scavenge for seals found on the ice itself.

Historically, Antarctica had not experienced the dramatic loss of sea ice seen in the Arctic. However, in the past five years, Antarctic sea ice has begun to retreat more rapidly. 

Seabirds may struggle to find food

The study suggests that as sea ice continues to decline, seabirds may be forced to fly further from their breeding grounds in search of food, or they may encounter shifts in where their food sources are located. This, in turn, could disrupt the ecosystems to which these seabirds belong.

Published in the journal Progress in Oceanography, the study provides new insight into how these changes in sea ice could affect bird populations that breed far from the continent. 

Study lead author Ewan Wakefield is a scientist from Durham University’s Department of Geography.

“Every winter, the sea freezes around Antarctica, with sea ice covering tens of millions of square miles. We found that albatrosses and large petrels travel hundreds of miles, some far into the area covered by this sea ice, and we think that they do this to feed,” said Wakefield. 

“In that case, Antarctica’s receding sea ice, driven by climate change, could affect not just the penguins, familiar to many people, that breed on the continent, but also huge numbers of seabirds breeding hundreds or thousands of miles away.”

Many species rely on sea ice

The experts analyzed the movements of seven species of albatross and large petrel, including northern and southern giant petrels, white-chinned petrels, and several species of albatross. 

Using satellite data collected between 1992 and 2023, the researchers tracked 2,497 foraging trips by 1,289 seabirds from South Georgia, a sub-Antarctic island about 1,000 miles from Antarctica. The research revealed that all seven species used sea ice-affected waters, though in different ways. 

For example, albatrosses largely avoided ice-covered areas, likely because of the difficulty in flying or landing on the ice. Instead, they fed in regions where the ice had melted and released concentrated nutrients. 

Southern giant petrels, on the other hand, ventured hundreds of miles into the pack ice during spring, likely scavenging for seals.

Shrinking sea ice levels

The researchers also observed a seasonal pattern, with birds moving north and south in sync with plankton blooms in the oceans – a phenomenon known as green wave surfing.

During the period when the satellite data was recorded, Antarctic sea ice was relatively stable. However, recent summers have seen earlier retreats and record-low levels of seasonal sea ice. 

Escalating impacts on seabirds 

According to Richard Phillips, co-author and leader of the Higher Predators and Conservation Group at BAS, these declines in sea ice, exacerbated by climate change, could worsen the already unsustainable human impacts on seabird populations.

While the study sheds light on how seabirds interact with sea ice-affected habitats, researchers acknowledge some limitations. They do not yet know exactly what the birds are eating in these areas, which future tracking and dietary studies aim to reveal. 

Additionally, the resolution of the tracking data wasn’t fine enough to show exactly how birds interact with sea ice on a small scale. Finally, the study didn’t cover the entire breeding period for several species, so it remains unclear how they might use these habitats during other times of the year.

Despite these limitations, the study underscores the importance of understanding how Antarctic sea ice dynamics influence not only the continent’s wildlife but also the seabirds that breed far away in the Southern Ocean.

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