"Even Antarctic Skuas Seek Local Favorites"... 'Localized Diets' Vary by Breeding Site [Reading Science]

Korea Polar Research Institute Quantifies Regional Dietary Patterns for the First Time Through Blood Analysis
A New Indicator for Detecting Early Signs of Ecosystem Disruption

It has been confirmed that the Antarctic skua, a representative apex predator in Antarctica, adopts a so-called "localized diet," changing its food sources depending on the breeding ground environment. Even within the same species, their menu varies significantly depending on whether there are many penguins or seal carcasses in the surrounding area, providing important clues for understanding the regional structure of the Antarctic ecosystem's food web.

A scene of a chick of Antarctic skua being fed, captured by the monitoring camera installed at Cape Moebius. Fish (a, b), penguin (c), seal entrails (d). Courtesy of the Korea Polar Research Institute

The Korea Polar Research Institute announced on the 31st that, after analyzing the blood of Antarctic skuas inhabiting four breeding sites in the northern Victoria Land region of the Ross Sea, Antarctica, they found that the composition of their diet differed distinctly by habitat.

The Antarctic skua is known as a typical opportunistic predator that is not picky about its food, adapting to the surrounding environment. However, there have been few detailed comparative studies on just how flexibly they change their diet, or how significant the regional differences are. In particular, comparative research in the northern Victoria Land area has been virtually absent for over 40 years.

The Antarctic skua utilizing various prey. Feeding on emperor penguin chick (a) and Adélie penguin chick (b). Fish (Emerald rockcod) regurgitated by the Antarctic skua (c) and placenta found in the Weddell seal breeding ground (d). Provided by Korea Polar Research Institute

Dr. Kim Junghoon’s research team collected blood samples from 41 adult Antarctic skuas at four sites near Jang Bogo Station between November and December 2021, then conducted stable isotope analysis. This method allows for a scientific reconstruction of the diet consumed over the past several days, enabling a more precise understanding of dietary patterns than analyses based on excrement or regurgitated materials.

The analysis revealed clear differences in diets by breeding site. At Cape Hallett and Inexpressible Island, where large Adélie penguin colonies are present, penguin eggs and chicks made up a high proportion of the skuas’ diet. Individuals near Emperor penguin breeding grounds at Cape Washington showed a relatively high proportion of Emperor penguin egg consumption. In contrast, skuas at Cape Mbius exhibited a more mixed diet, feeding on Weddell seal carcasses and placentas, Adélie penguins, and fish.

Antarctic Skua breeding grounds along the coast of North Victoria Land, Ross Sea, Antarctica. Cape Hallett, Cape Washington, Cape Mbius, Inexpressible Island. Courtesy of the Korea Polar Research Institute

The significance of this study goes beyond simply revealing gull feeding habits. Changes in the diet of apex predators rapidly reflect shifts in the distribution and population numbers of organisms at lower trophic levels, such as penguins, fish, and seals. The researchers explained that, as climate change destabilizes food resources, these dietary changes could serve as an "early warning indicator" for the first signs of ecological disruption in the ecosystem.

Dr. Kim Junghoon stated, "By monitoring changes in the diet of the apex predator Antarctic skua, we can quickly detect fluctuations in the distribution and diversity of lower trophic level organisms such as penguins and fish."

The results of this study were published in the international journal PLOS ONE. Shin Hyungchul, Director of the Korea Polar Research Institute, said, "This achievement demonstrates that the Antarctic ecosystem possesses distinct food web structures in different regions," adding, "Understanding such spatial differences will be a crucial starting point for research into the Antarctic ecosystem."

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