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Arctic bird turns down immune system to conserve energy in winter

The Svalbard rock ptarmigan sacrifices its immune system in the winter to conserve energy needed to keep warm and hunt for food. Photo by Andreas Nord
The Svalbard rock ptarmigan sacrifices its immune system in the winter to conserve energy needed to keep warm and hunt for food. Photo by Andreas Nord

April 28 (UPI) -- To survive the Arctic's frigid temperatures, animals must use their energy efficiently. According to a new study, one Arctic bird species, the Svalbard rock ptarmigan, utilizes a previously unknown energy-saving method.

No bird lives closer to the North Pole than the the Svalbard rock ptarmigan. To better understand how the bird species survives the extreme conditions, researchers analyzed changes in the bird's immune system during the winter and late spring.

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"We have discovered that the birds reduce how much they spend on keeping their own immune defense system up and running during the five months of the year when it is dark around the clock, probably to save energy," Andreas Nord, researcher at Lund University in Sweden, said in a news release. "Instead, they use those resources on keeping warm and looking for food. When daylight returns, their immune response is strengthened again."

When birds become ill in the middle of winter, scientists found, their energy levels drop compared to when they are healthy. The opposite occurs when the birds get sick during the spring.

"A weaker immune system is probably a part of all the adaptations that Arctic animals use to save energy in winter," Nord said. "The risk of being infected by various diseases so far north is less in winter than when it becomes warmer towards summer."

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The novel energy-saving strategy -- described this week in the journal of Experimental Biology -- is surprisingly risky. The bird doesn't have much an immune system to sacrifice. Scientists suspect the a strong immune system is less useful in the Arctic, where the Svalbard rock ptarmigan evolved.

"This may have negative consequences when the climate changes and migratory birds arrive earlier in the Arctic and leave later," Nord said. "More and more tourists also come ashore in places where people have not set foot before. Such a scenario paves the way for an increased risk of disease and may be a threat to animals that have evolved in the Arctic where a strong immune defense system might not have been needed."

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