Research Highlight: Birds of a Feather

Emperor penguins live comfortably in frigid Antarctic conditions thanks to a highly specialized feather coat. Researchers at Scripps Institution of Oceanography at UC San Diego plucked away the feathers of these dapper birds to uncover the source of their natural outerwear.

Scripps researchers Cassondra Williams and Jerry Kooyman collected emperor penguin carcasses from two different colonies in Antarctica to study the type and thickness of their feathers. They found a highly complex plumage structure that helps these birds maintain a cozy body temperature of 38 degrees Celsius (100.4 degrees Fahrenheit) during the harsh Antarctic winters.

The results, published in the journal Proceedings of the Royal Society B, show that a specialized type of down-like feather, called the plumule, is four times as dense as the bird’s other feathers and acts as its body’s major insulator. The team also discovered that emperor penguins do not have the highest feather density of any bird, as was previously thought. The white-throated dipper’s contour feather density is over six times higher than the emperor penguin.

During the chilly Antarctic winters where temperatures average -40 degrees Celsius (-40 degrees Fahrenheit), the already-lean penguins are shedding up to 50 percent of their body mass during an annual fast. The researchers found that as the penguins lose fat during the winter fast their feather density increases. 

“Unlike most marine mammals, which rely on a thick blubber layer to keep them warm, the emperor penguin has a relatively thin layer of fat that gets thinner during the winter fast,” said Williams, a postdoctoral researcher at Scripps and lead author of the study. “The increased feather density helps compensate for the loss of fat beneath the skin.”

One of the biggest challenges for the research team was to identify the best way to count the feathers and visualize the pattern under a microscope. The penguin’s densely packed outer contour feathers bend at an almost 90 degree angle, which made it difficult to see where they insert into the skin. 

“To increase the difficulty, any time we tried to move or pluck the contour feathers, a cloud of downy feathers arose from the penguin, said Williams. “However, this told us that there should be a lot of downy feathers beneath the contour feathers.”

Having a thick, insulating plumage allows the penguins to survive the Antarctic winter as well as dive to great depths in sub-zero waters.  The research findings have important implications for the conservation and health of this iconic species, and could lend new information to the design of better insulation and winter outerwear in the future.  

– Annie Reisewitz

Related Image Gallery: Birds of a Feather