This October 2012 video is called Svalbard rock ptarmigan (winter plumage).
From Lund University:
Arctic wildlife uses extreme method to save energy
April 28, 2020
The extreme cold, harsh environment and constant hunt for food means that Arctic animals have become specialists in saving energy. Now, researchers at Lund University in Sweden have discovered a previously unknown energy-saving method used by birds during the polar night.
Researchers from Lund University and the University of Tromsø have examined the immune system strength of the Svalbard rock ptarmigan in the Arctic. This bird lives the farthest up in the Arctic of any land bird, and the researchers have investigated how the immune response varies between winter and late spring.
When I was in Svalbard in June, I saw rock ptarmigans. Including a male which had spent the night on a telephone pole (safe from local Arctic foxes). He landed and mated with a female.
“We have discovered that the birds reduce how much they spend on keeping their own immune defence system up and running during the five months of the year when it is dark around the clock, probably to save energy. Instead, they use those resources on keeping warm and looking for food. When daylight returns, their immune response is strengthened again,” says Andreas Nord, researcher at Lund University.
The researchers found that when the birds become ill in mid-winter, their energy consumption drops compared to when they are healthy. However, when the birds become ill in late spring, their energy consumption increases instead.
“A weaker immune system is probably a part of all the adaptations that Arctic animals use to save energy in winter. The risk of being infected by various diseases so far north is less in winter than when it becomes warmer towards summer,” says Andreas Nord.
When Svalbard rock ptarmigan save energy in this manner, they do so by weakening an already weak immune system. According to the researchers, this is probably due to the fact that the species evolved in the Arctic where there has been less of a need for a very strong immune defence system.
“This may have negative consequences when the climate changes and migratory birds arrive earlier in the Arctic and leave later. 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 defence system might not have been needed,” Andreas Nord concludes.