Behavior

Belligerent Birds: Do penguins perform unprompted acts of aggression?

Paper: Penguins Strike Back: A Report on the Unusual Case of Adélie Penguin (Pygoscelis adeliae) Attacks on South Polar Skua Nests Distant from the Breeding Colony DOI: https://doi.org/10.3390/d13050181

 

An Adélie penguin. These penguins have the widest range of any penguin species, even though they only live in Antarctica. They are relatively small, with the largest individuals reaching 28 inches tall, and typically eat krill and small fish. Image by Liam Quinn via Wikimedia Commons.

Life in the Colonies

In Antarctica, penguins are a frequent sight. Of the penguin species that live on this snowy continent, the Adélie penguin is the most widespread. These penguins, like most other penguin species, form colonies, or large groups where individuals all live together. These colonies help penguins find mates and avoid being eaten by predators. This is because it is a lot easier to spot and eat one penguin all by itself in the white snow than it is to hunt one penguin in a crowd of thousands. These colonies also serve to protect penguins’ eggs and young from predators. Adélie penguins are fiercely protective, and will behave very aggressively if a predator make its way into a colony to try to eat their eggs or young.

In particular, south polar skuas, large white and brown birds, will frequently try to nibble on penguins. Adélie penguins will not only drive out the skuas that enter their colonies, but will also destroy skua nests that are anywhere near colonies, sometimes harming skua eggs. To scientists, this pattern made sense: if a penguin perceives the presence of a skua as a threat to itself, its home, or its family, it will try to get rid of the threat. With this reasoning, it would seem likely that skua nests that are far away from penguin colonies would be safe from penguin attacks. However, this is not always the case. Recently, scientists from the Korea Polar Research Institute observed some highly unusual Adélie penguin vs. skua activity that challenges what we have previously thought about the relationship between these two birds.

An Adélie penguin colony on Franklin Island in Antarctica. Penguins will socialize, mate, and raise their young in these colonies. By having a large group of individuals together in one location, each bird is much safer from predation than they would be on their own. Image by Lin Padgham via Wikimedia Commons.

 

A south polar skua in Terra Nova Bay, Antarctica. These birds make long winter migrations, ending up in the Pacific, Atlantic, and Indian Oceans. They are known for stealing food, particularly fish, from other birds. Image by Paride Legovini via Wikimedia Commons.

Capturing Combat

The scientists already had motion-capture cameras set up near eight skua nests to monitor their behavior. In December of 2020 and January of 2021, these cameras captured Adélie penguins aggressively forcing adult skuas out of three of the nests, even though the nests were nowhere near Adélie penguin colonies. It is unknown if the same penguins were to blame for all three attacks, or what exactly prompted the attacks in the first place. In all three cases, the adult skuas were forced to leave their nests, usually containing eggs or young offspring, and fly off. These attacks occurred during the penguins’ breeding season, which begs the question: why were the penguins not near their colonies guarding their own young?

Scientists hypothesize that perhaps these Adélie penguins were not successful during mating season, had no eggs, and were simply wandering around Antarctica looking for food and shelter. Since mating season tends to come with an increase in aggressive or unusual behavior in many animals, especially males, these attacks may have been the result of increased hormones. The skuas also gave warning calls as the penguins approached the area surrounding the nests, which could have prompted the penguins to investigate the sound.

An example of Adélie penguins chasing an adult skua out of its nest, leaving the young behind. These images are labeled #3 as this was the 3rd skua nest the researchers observed being attacked. On the left, the penguins approach the adult skua and use aggressive tactics to force it away. On the right, the penguins roam about the skua territory, with the young skua still visible. The young skua is circled in red in both images. Images are taken from Petherick et al., 2021.

The Importance of Interactions

By learning more about how these two birds, or any two species, interact, scientists can gain important understandings of how food webs work in different ecosystems. The Antarctic is under several threats, from climate change to plastic and oil pollution. By learning what behaviors are normal and abnormal in different Antarctic animals, scientists may be able to detect if something is wrong in an area before an issue escalates. This is because animals typically act strangely when their environment is negatively altered. In the case of Adélie penguins and skuas, it is clear that these birds do not get along, and do not need a concrete reason to behave aggressively towards one another. This information is incredibly helpful to zoos that may house both these species, and to researchers and conservationists who work in regions of the Antarctic where both of these animals are common.

If you would like to learn more about Adélie penguins, you can visit the Australian Antarctic Program website.

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