by Dr. Wayne Lynch
April 19, 2019
In Alberta this past winter we had the coldest February in 83 years. For many weeks, temperatures ranged between -20° and -35° C. At the same time we had an influx of wintering snowy owls and while I froze my butt taking photos of these magnificent birds of prey I wondered how they managed to cope with such temperature extremes. It turns out that evolution is a remarkable problem solver.
A basic principle in biology predicts that large owls lose less heat from their body surface than small owls do. This is one of the reasons why the heaviest owl, the snowy owl, lives in the one of the coldest climates, and the smallest owl, the desert elf owl, lives in one of the hottest ones. What this principle means to an owl is that the small species must rev up their metabolism to stay warm when the air temperature is still relatively high. This burns calories which must be balanced by fat reserves or an increased intake of food. Large owls, on the other hand, can withstand much lower temperatures before they need to increase their metabolism.
The temperature at which a bird’s metabolism begins to increase to offset losses in body heat is called its lower critical temperature. The lower critical temperature for the snowy owl is just above freezing at 2.5°C (36.5°F). This is the lowest critical temperature of any owl species tested, yet two other arctic birds are even better adapted. The common raven’s lower critical temperature is 0°C (32°F) and that of the willow ptarmigan is an amazing -6.3°C (20.6°F).
The cold tolerance of the snowy owl results from its large body mass and thick winter plumage. Zoologist Dr. James Gessaman measured the heat conductance through the thick feathers of the snowy owl. He discovered it was lower than any other bird except the Adélie penguin (Pygoscelis adeliae), and equivalent to the exceptionally warm pelt of the Arctic fox. Gessaman believed that the snowy owl could survive ambient temperatures lower than any recorded in the Northern Hemisphere.
To prove his point, Dr. James Gessaman subjected a captive snowy owl to increasingly colder temperatures. He first dropped the temperature to -55 °C (-67°F) and held it there for 3 hours. He followed this with 2 hours at -77°C (-106.6°F); and finally 5 hours at -93°C (-135°F). To put these temperatures in perspective, the coldest temperature ever recorded on the planet is -128.9°F (-89.4°C), at Vostok, the Russian research station in the center of the Antarctic Ice Cap. Amazingly, the snowy owl survived these lethal temperatures with no signs of frostbite.
Bio: Dr. Lynch is a popular guest lecturer and an award-winning science writer. His books cover a wide range of subjects, including: the biology and behaviour of owls, penguins and northern bears; arctic, boreal and grassland ecology; and the lives of prairie birds and mountain wildlife. He is a fellow of the internationally recognized Explorers Club - a select group of scientists, eminent explorers and distinguished persons, noteworthy for their contributions to world knowledge and exploration. He is also an elected Fellow of the prestigious Arctic Institute of North America.
Dr. Wayne Lynch
3779 Springbank Drive S. W.
Calgary, AB, T3H J5
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