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Why don't duck's feet freeze when they stand on ice? What do duck feet, Arctic foxes, and flamingos have in common? You'll find out when you learn all about countercurrent heat exchange with Jessi from Animal Wonders!

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Hi, I'm Jessi, and this is Animal Wonders.  I was recently asked by one of our young viewers how ducks keep their feet from freezing in a cold lake, and I'm excited to be able to talk about it.  


I'm constantly surprised by some of the incredible adaptations certain animals have to survive in extreme environments, like emperor penguins in the frigid cold of Antarctica, Egyptian sand fish, escaping into the sand of the desert, and anglerfish, thriving in the deep, dark of the ocean, so when I look at an animal like a duck, it's sometimes easy to overlook the fact that they can swim in seriously cold water or stand on ice and not have their feet freeze solid, and this is all because of an amazing thing called countercurrent heat exchange.

What's happening is the warm blood from a duck's body flows down their leg and comes into close contact with cold blood traveling from their foot back up their leg.  The close contact between the hot and cold blood brings the temperature of warm blood down and increases the temperature of the cold blood.  This does two things: the temperature of the cold blood going back into their body heats up so it doesn't bring their core temperature down and the warm blood gets colder before it reaches their foot, so the temperature of their foot and the temperature of the ice are closer together.

Let's look at this a little closer.  Heat exchange happens when there's a difference in temperature between two objects.  The bigger the difference in temperature, the quicker heat will move from the hot object to the cooler object.  If there's less of a difference in temperature, the heat exchange will be slower, so when the warm blood from a duck's body travels down their leg and gets cooled by the blood traveling up from the foot, the difference between the temperature of the ice and their foot gets smaller, which means that by the time the blood gets all the way down to their foot, it's quite cold and the heat exchange decreases.

Surprisingly, ducks that are standing on ice lose only about 5% of their heat from their feet and they lose 95% from their body, even though they're covered in warm feathers.  The countercurrent heat exchange system helps them survive in the cold temperatures, and the same system works for other animals, too, like Arctic foxes, who walk on and dig in snow for long periods of time.

This is Cas and he's showing off his amazing winter coat.  His fur will definitely help, but it's not the only thing that will help him survive in the cold.  Arctic foxes also have countercurrent heat exchange systems in their paws to keep them from freezing and to reduce the loss of body heat during the extremely cold winters.  You have super paws, buddy!

Now, countercurrent heat exchange systems not only work for cold weather animals, they also help animals who live in hot environments, too.  Flamingos are famous for their pink feathers and long legs, but not many people know that the waters they stand in can get incredibly hot.  The shallow waters they hunt for food in can get up to 115 degrees Fahrenheit, and they could quickly become overheated if they didn't have something to protect them.  Flamingos also have the same countercurrent heat exchange system in their legs like ducks do, but instead of keeping them warm, it helps cool them off.

Remember that the smaller the difference in temperature between two objects, the less heat exchange will take place, so for flamingos, their body temperature is cooler than the hot water they're standing in.  The cooler blood travels from their body into their leg and as it goes down, it intertwines with hot blood coming up from their lower leg and foot.  That heats up the cooler blood so when it reaches the water, it's closer in temperature so the heat exchange from the water is less dramatic than it would be if the temperature difference was bigger.  The hot blood then comes back up their leg toward their body and is cooled down by the blood coming down, which makes sure they don't pump hot blood back into their body, and you've seen flamingos standing on one foot, right?  They do this because it's more efficient.  Because they only have one foot in the hot water, it reduces the exchange of heat from the water to their body even more.

So this seemingly simple thing that ducks and flamingos can do is more complicated than it looks.  Thanks for being curious and learning with me.  If you'd like to continue going on adventures, be sure to subscribe, and if you have any questions you would like me to answer, leave them in the comments below.

Now, I love learning about animals and how their bodies work, which is why I recently watched this video called "What Animals See" on CuriosityStream.  I enjoyed revisiting some information I thought I knew pretty well, but realized I hadn't explored fully and now I'm eager to continue delving down the rabbit hole once again.  You can find the video on CuriosityStream, who was the sponsor of today's video.  They're a subscription streaming service that offers over 2,000 documentaries and nonfiction titles from some of the world's best filmmakers, including exclusive originals.  Get unlimited access starting at just $2.99 a month and for our audience, the first 30 days are completely free if you sing up at and use the promo code 'animalwonders' during the sign-up process.

Thanks, and we'll see you next week.