By Wendy Langham
Last week, we took a road trip to visit family, driving north along the eastern side of the Sierra’s. I debated whether or not to pack my warm (and ratty-looking) cardigan sweater.
Later that night I was glad I did: our hotel room in Lone Pine was cold and my feet were freezing.
I remembered my Grandma’s advice – wear a cap when you go to bed and your feet will stay warm. So I wrapped that cardigan around my head and neck and, sure enough, Grandma was right. My feet warmed up.
The next day, we saw a flock of Canada geese near a snow-bank and it got me to thinking: how do those birds keep their feet warm? Their lower legs and feet aren’t covered by insulating feathers. And I don’t see them wearing any stocking caps (with or without a maple-leaf patch). So how do they do it?
Canada Geese feet are uninsulated.
It turns out they don’t – keep their feet warm, that is. But they do maintain their core body temperature and avoid hypothermia, by minimizing the heat lost through their feet. They do this in part through a sophisticated adaptation in their circulatory system.
Bird legs contain both arteries and veins. The arteries (carrying oxygen, nutrients and WARM blood), flow from their body to their feet. Meanwhile, the veins (carrying carbon dioxide and COOL blood), flow from their feet to their body.
These blood vessels form a structure known as a “retia mirabilia“, (wonderful net), a complex intertwining of arteries and veins, where heat is transferred from the outgoing arterial blood to incoming venous blood. Biologists refer to this as a “counter-current heat exchange” system. Heat is exchanged (and conserved) before their blood reaches their uninsulated feet, thereby minimizing heat loss.
View of Mt. Whitney from Lone Pine.
Counter current heat exchange systems are found in all sorts of applications within the HVAC industry (heating, ventilation and air conditioning).
They’re used in everything from hot water heaters to industrial refrigeration systems. But they cost money to operate, something that must have been in short supply at that hotel in Lone Pine.
So I’m glad I had my cardigan as back-up plan, even if it is a bit ratty-looking.
Upcoming Outdoor Events:
Saturday, January 16, 8 – 10 AM. Bird Walk at Towsley Canyon. It takes some unique birds to stick around in our winters. Meet at the front entrance to the park. Beginners are welcome. Heavy rains cancel. For map, click here.
Saturday, January 23, 1-3 PM. Hibernate, Migrate or Tolerate. On this easy afternoon walk at Towsley Canyon, we’ll take a look at how animals and plants cope with winter. Heavy rains cancel. For map, click here.
You can listen to stories like this every Friday morning at 7:10 a.m. on “The Hike Report”, brought to you by your hometown radio station KHTS (AM1220) and by the Mountains Recreation and Conservation Authority.