Why Do Birds’ Feet Not Freeze During Winter?

If you’ve ever ventured out on a cold day with your feet completely exposed, you know all too well how terribly it hurts. It’s almost impossible to stand or even walk for too long on a cold surface without it turning into a nasty experience or somehow hurting one’s feet. Yet, there are many bird species that seemingly do exactly that without any problem! In fact, there are many species, like penguins, ducks, gulls, etc. who spend a considerable amount of time on ice or icy water itself.

So, how do birds manage to keep their unprotected feet from getting a nasty sting (or frostbite) while ‘chilling’ out (pun intended), just like this bird here:

Short answer: A lot of birds simply pull their legs and feet closer to their body, some fluff up their feathers to trap warm air, while some species keep warm courtesy of their countercurrent exchange system.

Some basic methods of shielding from the cold

There are almost 10,000 species of birds all over the world; some of them live in tropical areas, where they enjoy sunlight and warm weather for a good part of the year, while others live in polar regions, like Antarctica and the Arctic circle, where they have to deal with extremely cold temperatures for a significant chunk of months. Consequently, there are various ways these birds can protect themselves from cold.

robin bird

Birds’ feet have a small surface area (Image Credit: lawrieephipps0 / Pixabay)

There are certain basic techniques that many birds use to keep themselves warm. For starters, birds generally don’t have large feet (in proportion to their body). Thus, the loss of heat through their feet is not that high in the first place. Furthermore, birds are warm-blooded, which means they can maintain their core body temperature and hence adapt to their ambient temperature.

Some species of birds (shorebirds like the common buttonquail, water thick-knee, quail-plover etc.) simply pull their feet towards the core of their body, just like how we tend to tuck our limbs together to keep ourselves warm.

water-thick-knee-bird

A water thick-knee bird (Image Credit: Greg Miles / Wikimedia Commons)

Since birds are warm-blooded, they can maintain their core body temperature, regardless of the coldness of the ambient temperature by increasing their metabolic rate. It works like this: when the ambient temperature drops, birds raise their metabolic rate (just like humans) to prevent their core temperature from falling.

Conversely, when the ambient temperature is high, birds mobilize water and lose heat through evaporative cooling (akin to sweating in humans). Some birds, like black vultures, excrete onto their unfeathered legs to aid cooling through evaporation.

Behavioral techniques

Many birds ‘fluff up’ their feathers to trap warm air between them, effectively adding a natural layer of insulation between their body and cold surroundings, just like a sleeping bag, only a natural one.

Owl fluffing up

An owl fluffs up (Photo Credit : Mark Glenshaw / Youtube)

To make things warmer still, birds often tend to stick their bills under their wing feathers so that they can breathe warmer air. Birds also tend to huddle together in groups to share each other’s body heat and stay warm as a collective. A few species (like the snow grouse) hide in snow burrows to seek warmth.

Putting on weight

Furthermore, certain birds also use a rather unappealing, yet highly effective technique to stay warm during long winters – they just eat a lot! Birds generally need to eat a lot to keep going, so stuffing themselves with food is not that big of a problem. Besides, it’s not just a big plus for their energy reserves; it also helps to create an additional, natural layer of insulation fat to shield them from the cold.

Fat bird meme

Countercurrent exchange system – A biological advantage

Most birds use the methods mentioned above to keep themselves warm, but there are some birds, like ducks, that do not have small feet and lack scales on their feet (which helps to minimise heat loss). On the contrary, their feet are particularly large and flat (which is the worst if you’re looking to minimize heat loss). To add to these woes, ducks and gulls spend a significant amount of time standing in or above icy waters. So… how do they manage to protect their feet?

Swan duck bird in cold river

A bird stands in icy waters without a worry in the world (Photo Credit : Pixabay)

The saying ‘Nature protects all its subjects’ couldn’t be more apt in this case. To protect their feet from cold, such birds have a fascinating blood flow system called the countercurrent exchange system. In this kind of circulatory system, blood leaves the bird’s core (trunk) at a warm temperature, while arterial blood returning from the feet comes in at a lower temperature.

Dird leg diagram

As the cold blood from the feet travels towards the core of the body, it picks up most of the heat from arterial blood due to conductance. The fact that blood vessels are packed closely in the birds’ feet helps too.

This way, the blood that reaches the bird’s feet is already quite cold, which means it doesn’t have much heat to lose to the surroundings. This is why ducks and gulls can stand in icy waters (with their feet just above freezing temperature) and still maintain a core temperature of 104 degrees Fahrenheit.

All this talk about ducks and their feet really makes me think: what would it be like if humans had the same kind of circulation system to deal with extreme cold? Maybe we could take more trips to Antarctica and have fun like these guys:

References:

  1. How Do Birds Stay Warm? – Beyond Penguins & Polar Bears – Ohio State University
  2. Countercurrent Heat Exchange – Minerva Program – Union College
  3. Avian Respiration – People Search: Eastern Kentucky University
  4. Temperature Regulation & Behavior – Stanford University
  5. Birds Reduce Their Heating Bills In Cold Climates – The University of Melbourne
  6. Today I Found Out
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About the Author:

Ashish is a Science graduate (Bachelor of Science) from Punjabi University (India). He spends a lot of time watching movies, and an awful lot more time discussing them. He likes Harry Potter and the Avengers, and obsesses over how thoroughly Science dictates every aspect of life… in this universe, at least.

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