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Skuas: Aerial Terrors of Antarctica

by Caitlyn Bishop Blog

Antarctic Peninsula

Regions: Antarctica

Skuas: Aerial Terrors of Antarctica

At first glance, the skua looks like a larger, darker-looking sea gull. Looks can be deceiving, however. As once of Antarctica’s top avian predators, they’re tough, they’re mean, and they’re unforgiving. Together, the brown skua and south polar skuas patrol the shores of King George Island, always with an eye out for easy prey or unsuspecting field biologist.

Working With Skuas

The brown skua is the larger of the two species, with a large, brown body, a sharp, falcon-like bill, and tiny claws at the end of its webbed feet. It goes without saying that avian predators with sharp beaks and nails are difficult to work with.

The south polar skua, the smaller of the two, has distinctive tan highlights to its feathers, and tends to be a lot more shy than the brown skuas. King George Island has historically been prime real estate for both species of skua during the breeding season. The plentiful penguin populations, proximity to the ocean, and rocky, protected habitat make for an excellent breeding spot. From October to March, scientists monitor the skuas on a weekly basis, track their egg laying schedules, reading adult skua bands, and monitoring the chicks.

Establishing a Territory

Each skua pair has their own unique breeding territory that they occupy during the breeding season. Once a breeding pair has established their territory, the pair will scrape a small depression in the ground and lay her eggs. Together, they’ll take turns incubating the eggs. While one is in charge of sitting on the nest, the other will head out to sea to look for fish or cruise through a penguin colony looking for a meal. Skuas don’t need to worry about having their eggs potentially exposed in the open air if they happen to both be away from the nest at the same time. There are no predators in Antarctica to the skuas or their eggs. The only concern that may arise is a rogue skua that may threaten their territory. This may result in territory shifts during the breeding season.  

Where Do the Skuas Play?

During one particular field season on King George Island, on the South Shetland Islands, small, satellite-transmitting tags were attached to a group of skuas’ bands to look at how far they travel for food, and how long their foraging trips last. This information can help scientists better understand the ecology of the skuas, and help them to conserve their populations in the future. The GLS, or global location sensing tags can detect when the skua has landed in the water, when they are in flight, and when they’re on land. The information that is stored on the tags can be rendered into a detailed map to show their exact movements. But first, the tags must be placed on the skuas, which means the scientists actually have to trap them. Their sharp intelligence and general wariness of humans adds a level of difficulty to this process that can last for hours. A monofilament noose is the best tool for the job, coupled with a large net for backup. The monofilament noose is placed on the ground within their territory, and is surrounded by raw meats to attract the bird into the trap. When one of their legs looks like it’s inside the noose, the line is vigorously pulled, and the skua is trapped. The GLS tag is placed on the leg with the metal band with a small zip tie, and then released. Two weeks later, it’s time to download all of the information that has been accumulating, which means that the scientists now have to recapture the skua. If it wasn’t hard enough the first time, the second time around isn’t any easier. Sometimes, the skuas will get the better of the scientists, and fly off with the transmitter with no intentions of giving it back. Luckily, the transmitter is harmless to the bird, and will eventually fall off.

A Skua Never Forgets

After working with the brown skuas for several weeks, they start to get comfortable with the repetitive exposure to humans, and begin seeking revenge. Wearing the same clothing, backpack, or even sunglasses when making nests visits can teach the skuas who you are, making them more likely to start attacking before you can even get into their territory. Their defense mechanisms are nothing to look forward to. Before even getting to the nest, the parent sitting on the egg will begin to make “alarm calls”, or loud vocalizations that alert the other parent of an intruder. Together, they’ll gang up on the intruder, peck at their head and face, grab at clothing with their sharp bill, and dive-bomb. The dive-bombing can be the most painful, as they’ll aim for your head while simultaneously screaming at the top of their lungs.

When the Chicks Arrive

While the eggs are still incubating, scientists record their length, width, and weight. Egg size and weight can be an indication of parental health. Over time, the scientists keep track of how long the egg incubates, and based on when it was laid, they can predict the hatch date to within a two to three day accuracy. When the chicks arrive, the scientists place a metal band with a unique numerical code on their leg, which they will wear for the rest of their lives. With any luck, the skua chicks that are banded during one field season will return to their hatching grounds the following year and rear chicks of their own.

Seasonal Skua Problems

An Antarctic ecosystem is a well-oiled machine. If you remove or alter even the smallest cog, the whole system is interrupted. What keeps the machine oiled in King George Island ecosystem is Antarctic krill and sea ice. The Western Antarctic Peninsula is currently experiencing an increase in the melting of sea ice due to global climate change. Without plentiful sea ice, the krill have nowhere to aggregate and breed. Adelie, Gentoo and Chinstrap penguins all rely heavily on the krill, and time their breeding schedules with the emergence and breeding of krill. If the penguins start laying their eggs at a different time every year to better line up with the krill emergence, this can mean bad news for the skuas, who rely heavily on penguin eggs and chicks during the time leading up to their egg laying and during chick rearing. Now everyone is out of synch, which can result in a decrease in resources for the skuas. On King George Island, this ecological cascade effect has resulted in the increase amount of time spent traveling for food by adult skuas. This means more time spent away from the young chicks, who can fall prey to other hungry skuas that have found themselves in the same predicament.

Where Can I See Skuas?

An expedition to the Antarctic Peninsula will yield a spectacular insight to the southern hemisphere’s distinctive fauna. During your Antarctica cruise you’ll no doubt cross paths with brown and south polar skuas. Their distinctive behaviors, such as raising their wings up when feeling threatened, loud vocalizations, or general boldness and curiosity set them apart from the many other species in the area. They’re truly unique in their ways! 

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