Why Birds Don’t Get Cold Feet | Hacker News Reader

Why Birds Don’t Get Cold Feet

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207 pointspmontra108 comments

This is anecdata. I am also not a bird.

Inspired by Wim Hof, I've started doing short barefoot snow walks. Within days, even between multiple walks on the same day, my feet became more cold-tolerant.

They now recover from the cold faster, stay warm in the snow longer, and when I'm indoors, my feet are no longer cold without socks.

My feet used to be cold to the touch and feel cold subjectively without socks.

I used to never be cold. Could sit in open below 0C air after a shower without cooling down. I never really wore thick sweaters, where some would insist in them.

Then I moved to a Mediterranean climate. When I go back now, I find I've become a wuss. Can't handle cold at all anymore.

Don’t know if basing your identity on reaction to weather is a good strategy, but your body adapts. And that’s the reason you don’t die during a Mediterranean summer.

I always love that in the spring and fall with the warm days I enjoy a nice 60F/16C evening and leave the windows open but then comes winter and those numbers just feel cold.

the human body adjusts but we don't notice is as much when we let the weather change around us instead of moving to where the weather has already changed

I don't often choose what I wear, though I'd choose scratchy wool over most materials. I find that layering is a great strategy, and usually wear 3-5 layers in most weather conditions.

Who chooses what you wear?

Depending on your worldview, it is "circumstance" or "the Universe" or "entities beyond choice".

I've chosen to abstain from buying clothes, so I get most of them by finding them in donation piles or from hand-me-downs.

Out of this selection, I pick the lightest, most comfortable, and least dangerous, layering from smallest to largest, and softest to most elements-durable.

Wool my friends. It is the only way.

but wool is so itchy and scratchy, isn't it?

"Wool" is a very broad category that pretty much means "material made out of some kind of animal hair". And since there's quite a few animals with hair, there's quite a few types of wool. I suggest trying high quality cashmere (note: cheap cashmere is typically mixed with other types of wool).

It depends on the wool. Finer wool like Merino wool tends to be nicer to wear directly on your skin. But you don't have to do that. You can and should wear cotton underwear. The extra layer keeps you even warmer and means you won't have to wash your outer wear all the time (wool should not be washed more than is absolutely necessary and ideally not at all). You'll also find heavier garments encase the wool in an outer material like cotton. You can get cotton duvets like this and they are wonderful. You can use them all year round. I will never go back to polyester again.

Have you tried pashmina? If there existed a real invisibility cloak, it would be made of pashmina! Soft, thin and magically warm

Wool socks are amazing. Warm and more importantly dry.

In a similar way down comforters are wonderful (get the right weight).

Don't you find wool not stretching is a real problem? I struggle to get well-fitting wool socks that I can also get around my ankle, as they have no stretch.

Did you know people used to use sock suspenders to keep their saggy wool socks up before we started to use synthetic fibres for socks?

I think my wool socks have a little synthetic fiber to help with that.

I tried less expensive wool socks, like from costco, and they were too warm and moist.

Then I tried darn tough wool socks and they are always warm and dry - even in summer.

It's not a problem if you find appropriate quality and thickness. One example is Icebreaker Ultralight socks. I use them in summer and they are rather thin.

> One example is Icebreaker Ultralight socks.

The website says they're actually 38% polyamide and 2% elastane. I think they're 'wool mix' socks rather than wool socks.

Indeed. I think that is to allow them to stretch. If you take something like a shirt, for example, it'll be all merino wool.

EDIT: Also I see that the proportions differ based on the type of socks.

Try bombas wool. Great everyday wool sock

I've never tried bombas wool, but I have a pair of bombas socks which were gifted to me, and other than being quite tight, they are serviceable. Make sure you get a large enough size.

Bombas are one of the few brands I would recommend to anyone because they donate one pair of socks for each that you buy.

Even more importantly: wool still insulates really well when wet.

I thought so too. At some point, I realized I'm allergic to wool and that was why it made me itch.

FWIW.

Wool with short fibers thick tends to be. Wool with longer thinner fibers like merino is much better.

This used to bother me, but it doesn't anymore. Somehow, I got over being bothered by wool's scratchiness, and even began to see it as a good quality.

I think this is an unintended consequence of my meditation efforts to dissipate my annoyance reaction.

Always use cotton as a first layer, because you can just put it in the laundry. Cleaning my woollen coat is more difficult than changing a cotton shirt underneath it.

Also: most “wool” is polyester because it’s like 10 times cheaper.

Cotton remains damp after you sweat and eventually also stinks of sweat. It's not a good base layer in cold weather. A lot of merino wool products are easy to clean and maintain. I have never seen polyester called wool.

No don't, you're going to be in for a bad time if you wear cotton as a base layer in -10C weather.

If you wear cotton socks and they get wet you might lose tour toes.

Most wool is definitely not polyester. At least not in Scandinavia.

This is good - potentially even life saving - advice if we're talking about doing serious activities outdoors. And in that case, even wool is probably best replaced with synthetics that are lighter and dry quicker when wet.

For around town, though, a cotton base layer and wool works pretty well.

I must side with the other replies to your comment.

I have been wearing cotton as my top base layer for a while, and it is not great at staying dry or drying out while damp.

I'd certainly choose it over any synthetic fabric, but once you go over that low mark, just about anything is better, e.g. wool, linen, help, silk, etc.

maybe they mean "grow wool", not "wear wool"

Acclimatisation is real. I've noticed a trend in the UK over the past 20 years or so. Previously many people, like my parents, used the central heating minimally. It would come on in the morning just to take the edge off in the winter. But that was pretty much it. Nowadays people are trying to keep their house the exact same temperature year round. That means it's warm in the winter and (if you have ac) cold in the summer. But people never acclimatise to the outside temperature as a result. So outside always feels way colder than it really should, or way hotter.

This winter I've reduced my study temperature (where I work every day) from 21 degrees to 19 degrees. It didn't take that long to acclimatise and now I'm not only saving money, I'm more closely acclimatised to the outside temperature.

I think ideally we wouldn't use thermostats, but instead use a system that adjusts inside temperature some percentage towards the ideal. So in winter when it's 0 degrees outside it's 17 degrees inside, and in summer when it's 30 degrees outside it's 25 degrees inside. Just think of the savings and how much nicer it will be to go outside when you're acclimatised.

The problem with that is that modern houses are very well insulated and unfortunately the insulation also traps moisture. If it gets too cold water condensates in the walls and mould can form. 17° in my experience is too cold and poses a risk.

> 17° in my experience is too cold and poses a risk.

Interesting, I have my thermostat set to 17° and the house is only 15 years old. What temperature should it be set to?

If you have no issues with mold than it's totally fine. It really depends on lot of variables, like outside temperature, humidity in your region, the quality of the insulation and building materials. But given the right (wrong) circumstances too little heating can become a real problem.

Interesting. From my experience, coldness of feet is correlated with blood circulation. There are periods when my feet are cold (going together with the restless legs syndrome at night), and I think it goes away when circulation improves. My theory is that exposing feet to elements is another trick to improve blood flow to them, I’ve been meaning to try that.

If you don't have any snow to walk through, just give 'em an ice water dip. You can do your whole body, too, with similar benefits. It's uncomfortable, but what isn't...

In my experience, and I've not found any studies to support this, restless legs correlates with oxygen levels vs carbon monoxide and/or carbon dioxide levels. Check your air.

It’s also highly correlated to issues with dopamine, which is why it’s an extremely strong symptom in opioid withdrawal

Yes, are bodies are wonderful and still mysterious miracles of spaghetti code.

Maybe oxygen then? Worse circulation or carbon monoxide could be involved, then.

I don’t think there’s anywhere for CO to come from, however air quality varies (CO2 levels easily reach 1000 ppbv at times).

Yes, that's what I meant. I've edited my comment.

>restless legs correlates with oxygen levels

yep, my RLS has pretty much gone since i started iron&B12 supplementation after i discovered anemia on my blood test (i have a condition affecting B12)

+1 for ice baths. I used to do them regularly when I ran cross country. Invigorating.

I have this with cycling. In the winter I never wear gloves (hate to carry these around), and when going about in the first cold days your fingers quickly go numb. By wriggling them and with body heat generated after a while they become warm, and you can even place them comfortable on the iron parts of the steering wheel. After some days in cold weather like this they don't go cold at all anymore.

Unfortunately doesn’t work for me. I have (self diagnosed) what is called raynaud syndrome where my body sends a signal to immediately draw the blood out of the hands when it’s very cold. They literally turn white. I need to cycle really hard and stop for a couple of minutes so that there is less cold airflow to get them back and usually they get cold again over longer rides. This is only a problem at below say 5-6 degrees but it’s very annoying.

You should specify which Winter you're experiencing. I'm assuming you aren't in sub zero temperature

I wear gloves for the first 3 minutes of cycling. After that heating has booted up, circulation has made a first full cycle and unless its very windy and snowy, I take my gloves of and my hands stay warm for the rest of the ride. Nice feeling actually.

Hot and cold treatments were used to kill infection before we invented antibiotics.

Not sure how pertinent that is to your experience, but it's the first thing that comes to mind.

Yep, immunity strengthening is a nice bonus.

Well, what I was actually thinking was that cold treatments could be killing off unrecognized, low-grade chronic infections and that may be leading to improved circulation and improved homeostasis.

Feet are notorious for being impacted first and worst by any circulation (blood) problems, which is why diabetics sometimes lose one or both feet to it (have them amputated, cuz reasons). And oxygen is a known means to kill certain kinds of infections (a la HBOT for Gangrene).

I think it's more likely a circulation workout.

But, sure, anything is possible.

I don't have a proper opinion on Wim Hof and his methods. On one side, he seems a nice, genuine person. On the other, I've read things that didn't necessarily add credibility to his methods.

Plus, his appearance on Gwyneth Paltrow's show (considered by many non scientific) was a bit of a downer for me.

I have friends who followed a workshop with him and had good results.

He also claims to have studies that support his method. I don't know if that's true, but I would look there more than the shows he's been on. If he wants to reach larger audiences, he will surely accept any invite.

If you see him speak in person, like in a documentary, he always seem high on adrenaline. Don’t know whether thats a good or bad thing.

What if it is neither good nor bad?

Indeed! I just don’t know anyone who is this hyped all the time.

I think it is just a matter of functioning at one's peak efficiency and health. I have experienced that state when I abstain from all the things which tend to drag down my state, including but not limited to processed foods including anything with added salt and sugar, coffee withdrawal, dehydration, inadequate sleep, lack of exercise, unchecked negative thinking.

One can spend all of eternity forming a "proper opinion", based on third-party information ten times removed, and end up having not moved an inch... -or- actually take a leap of faith and try it, and have a real first-hand experience and information knowledge.

Warm bloodedness (endothermy) would not be possible without countercurrent exchange in nasal passages. We have intricate bones there that capture heat and humidity in exhaled gas, then transfer it back to incoming air on the next breath. Without this the energy cost would be prohibitive. Structures like these in fossils are used as markers of the evolution of endothermy in ancestors of mammals and birds.

I'm not a biologist, but shouldn't this only matter in cold climate?

If the climate is warm enough the animals actually would need to have ways to actively cool down, like through sweating. Would capturing heat from their expiration still be needed?

Wouldn't the mechanism work wether it's warm or cold relative to body temperature? The relative warmness of the breath could be captured on the way out and heat up incoming air, or it could capture the relative coolness of the breath on the way out and cool down incoming air.

This doesn’t explain why the interstitial fluids and cells themselves in a birds feet avoid freezing. Presumably, either their feet can simply be maintained at slightly above freezing or they use some form of antifreeze.

Does anyone know?

The article says this:

It’s pretty much all tendons and bones. So, unlike your human foot, which contains plenty of moist muscle tissue, a bird’s foot contains only very little fluid in its cells.

It seems like they do keep their feet above freezing. Which is counter to the article’s: “Given a bird’s frantic little heart, blood simply rushes by way too fast to freeze.” As the blood never actually reaches freezing temperatures.

“Warm blood moving toward the feet is cooled, which helps penguins keep their feet at temperatures just above freezing.” http://blogs.britannica.com/2011/01/penguin-feet-avoiding-fr...

The only things I can readily find just reiterate what is in this article about heat exchange in the blood vessels:

https://www.birdnote.org/listen/shows/why-birds-feet-dont-fr...

https://en.wikipedia.org/wiki/Bird_feet_and_legs#Thermal_reg...

One article I briefly looked at indicates there isn't as much study of avian ...something ....as mammalian. Maybe fattiness because I was wondering if they have any adipose tissue in their feet. Oil is harder to freeze than water.

I also googled for info about saltiness and bird feet, which helped me find some article about "antifreeze" in various species but it barely mentions birds in passing:

https://www.nytimes.com/2010/01/19/science/19creatures.html

Salt gets used to de-ice roads in winter because it changes the freezing point of water. But I am not readily finding anything that indicates we have found a chemical antifreeze mechanism in bird feet.

It may exist but not have been studied or looked for at all.

Edit: Though upon closer examination, the article about animal "antifreeze" talks about proteins that serve that function, which is a new one on me. So someone else would need to google up info on protein structures of bird feet and speculate if those could have antifreeze properties. I don't know that much about protein and its impact on physiological characteristics (other than, you know, it's pertinent to insulin resistance or something, which most diabetics seem unfamiliar with while we blame everything on fat and overlook the role of lack of muscle).

I think you’re misunderstanding how essential and varied proteins are. In simple terms they are the nano machines which actively do stuff in cells. https://basicbiology.net/biology-101/molecules-of-life

Essentially, DNA encodes Proteins which manipulate everything else. Human cells for example have on the order of 1 to 3 billion proteins, remove water and over half of what’s left is proteins. https://en.wikipedia.org/wiki/Protein

Yeah, I'm well aware that DNA encodes proteins which, when deployed properly, become nano machines.

I have a genetic disorder that is essentially a salt-wasting condition. It also results in my body significantly misprocessing fats and oils.

So I know something about salt and about fats and about how those interrelate with biology and how those can weirdly impact things.

Beyond being aware of how those nano machines get broken when protein misfolds happen at the cellular level, I haven't taken much interest in the chemical properties of protein. It wasn't essential to my survival.

So someone else can look up the proteins of bird feet and go crazy with that if they care to. It's not my niche.

yes but the parent commenter seems to think this is not adequate to explain it.

I don’t know, but I’m always amazed at how animals don’t just all freeze to death and die. I know that many do but still.

Evolution? We are rather different from those species that have adapted to colder climates. But there really is quite many ways to combat it. Move underground or even under snow, eat enough. In general have sufficient metabolism and insulation.

They're always out there, so their bodies adapt.

We're capable of it too, many of us just don't try because it is uncomfortable at first.

I think it's worth doing, because the process of adapting also conditions our bodies to be stronger and more resilient in many ways.

Cold conditioning has been proven to boost the immune system and many other health factors.

https://www.wimhofmethod.com/cold-therapy

Their feet are kept slightly above freezing by the very mechanism explained by the article. It's a heat exchanger, basically. Warm blood from the heart is used to keep cold blood in the extremities from freezing, and this "double loop" system is much more efficient than pushing warm blood directly into the feet where thermal losses would be much greater.

Exactly. I want to know what cellular metabolic tricks they use to keep their foot cells working at just over freezing temperatures.

What about a simple anti-freezing agent used in something like a car radiator? This doesn't seem like it should be such a mystery in the age of Google and Wikipedia. There are bacteria and other multicellular organisms that function just fine in extreme cold environments.

See extremophiles, psychrophiles, etc.

Freezing is not the only threat. The functioning of cells depends on proteins that only work effectively within certain temperature ranges. Ectotherms tend to have multiple different pathways for a given process that cover several different temperature ranges while endotherms don't. So, do birds have that? Do their feet still grow, heal, fight infections when they're cold or do they depend on time spent with their feet warm?

I'm not sure if I can trust a random article on the internet but I do (mostly) trust my eyes. I have lots of small bird-feet-tracks outside my window where they have melted the snow. So clearly either they are not freezing because they are warm or they are covered in anti-freeze.

Or the pressure on the feet puts marks into the snow.

Countercurrent exchange is a remarkable thing that every engineer should know about.

Can you list some examples of where this is used in engineering (software or otherwise)?

Milk pasteurization is one of the best examples.

You start with milk at 4C, heat it to ~70C via heat exchanger (+66C), then 75c via heating (+5C), wait 15 seconds for pasteurization, cool down to ~9C via heat exchanger (-66C), then just chill to 4C via refrigeration (-5C).

This requires ~1/14th the energy to heat the milk and also rapidly cools it down below ambient temperature afterwards saving even more energy.

You see similar approaches for a lot of large scale chemical processes.

I had never heard of this, the use of already existing heat is amazing! Do they run 24/7? If not, they must use a lot of energy to cold start the process.

One classic example I always hear about efficient use of heat exchanger is the building of.swimming pool in the same building as ice rink. The heat produce cooling one is used to warm the other.

Open hearth steel mills. Regenerators in some gas turbines. Dialysis machines. Liquid-liquid extraction. Isotope separation cascades. Fractional distillation columns. Most heat exchangers are countercurrent, as it minimizes entropy generation.

A fresh air exchanger in an HVAC system. The fresh external air coming in is [warmed|cooled] by the interior air being exhausted.

Also know as a heat recovery ventilator. If you are building a new house, read up on these, as you probably want one.

HVAC systems. The outgoing air goes through a heat exchanger to transfer heat to the colder incoming air.

As far as I know, most HRVs are cross-current. I don’t know why.

Avoiding condensation?

Rotating disk heat recovery devices can also recover humidity.

I think most HRVs have condensation drains, so I doubt that avoiding condensation is the major consideration.

I would guess it’s more of a geometric consideration. A square cross-current heat exchanger can have each port on a different side, so the whole perimeter is used. A counter-current exchanger would have two ports on each of two sides and no ports in the other sides, leading to a rather more complicated and larger arrangement.

Check Wikipedia, the article has examples:

https://en.wikipedia.org/wiki/Countercurrent_exchange

The page also talks about a variant, countercurrent multiplication. There's a really nice example of this in hydrogen isotope separation. The technique, called CECE (Combined Electrolysis Catalytic Exchange), was developed in Canada for production of heavy water and removal of tritium from heavy water.

The centerpiece of the system is a catalytic exchange column. In the column, liquid water flows down, while hydrogen gas (of various isotopes) flows up. At each point, a wet-proofed catalyst promotes the exchange of hydrogen atoms between the water and the gas. In equilibrium, protium partitions more into the gas phase than into the liquid, so as the gas goes up the tower the heavier isotopes are stripped into the liquid phase and carried back down. At the bottom, the water is fed into electrolysis cells to produce gas to feed back into the tower. Over time, the water in the cells becomes enriched in heavier isotopes and can be tapped off.

With this system, any H2 electrolysis plant could modified to also produce heavy water. This has troubling implications for nuclear proliferation in the coming "hydrogen economy", as heavy water reactors can be small and easy to hide, and have been used in the past for nations to enter the "Nuclear Club".

Intercooler, dialysis

I feel like I’ve read articles about birds feet not getting cold from four different sources (Reddit, YT, Twitter and now HN) in the past week. Why is everyone suddenly so interested in birds?

Must be a submarine PR campaign by Big Bird.

Because of… how the social media, and your social bubble, fundamentally works? An article that becomes popular on one site naturally spreads to other sites by people sharing it. Also, the Baader–Meinhof effect, which primes you to notice things you've learned about recently.

IDK but I picked up one of my hen this morning and thought "Wow, her feet are COLD."

Bird feet may not normally get frostbite or whatever, but they certainly do get cold.

That's a feature, not a bug. It prevents losing energy.

I was sleeping on a balcony in Hawaii on a trip, when I woke up there was a one legged pigeon that was hanging out right next to me. Ever since then I noticed quite a few birds with a missing foot. Makes me wonder how much sensitivity birds have in their feet.

Looks can sometimes be deceiving with regards to one-legged birds.

My pet goose (yeah, weird pet, but she was from an egg I saved and incubated) does a trick where when she sleeps she puts her head under under a wing and lifts a leg up -- she sleeps on a single leg with her head tucked like a big ball of balanced feathers with tremendous balance and grace. She tucks her leg up so high into her down fluff that you can't see it at all. She only wobbles a bit when she's deeply asleep -- never falling.

Here is a picture of a different species of goose (I have a Toulouse) doing the same behavior[0]. It's not terribly uncommon among birds.

Of course REAL one-legged birds exist, just wanted to mention that they like to confuse people once in awhile :)

[0]: https://p0.pikist.com/photos/373/410/nature-wildlife-bird-go...

> My pet goose (yeah, weird pet, but she was from an egg I saved and incubated)

Did you find the egg in the wild? I was under the impression commercial eggs were generally not fertilized.

On a different note, how does your goose behave toward people? My dad still tells stories of the cute easter chick he raised, which grew into a non-cute rooster that took over the back yard and terrorized everyone except my grandmother.

Outside of the US it is not uncommon. I believe US eggs are washed with a detergent which kills salmonella and sterilizes any fertilized eggs. As a side effect, US eggs are more prone to spoiling at room temperature.

Anyway, in Europe or Asia one can buy 30 eggs, incubate them for a few days, and hold them up to a lightbox one by one. Probably at least one of them will be fertilized.

I know the behaviour you are describing, but the pigeon had its foot severed at the ankle. I saw the actual leg, so its not that it was hiding it. Looked more like pirate stub.

Ah , that's too bad.

This article mentions a correlation between pollution and loss-of-limbs in urban pigeons. They even mention it may due to human hair entanglement from hair salons as a primary culprit -- that seems far fetched to me, but who knows.[0]

I tend to think that it's mostly just environmental entanglement, pigeons are pretty curious animals.

[0]: https://www.birdspot.co.uk/bird-brain/why-do-so-many-urban-p...

I always wonder whether it is the spikes that are used to deter birds from sitting on ledges. At least that's what comes to my mind whenever I see birds with mutilated feet. :/

Based on my trips to Hawaii, my guess is that a cat mostly caught that pigeon, and the pigeon lost a leg in the process.

Many birds are victim to string-foot.

While building nests, birds will find and pick up man-made string, which becomes tangled in their feet, eventually cutting off circulation and killing the foot.

https://www.google.com/search?q=pigeon+string+foot

https://www.pigeonrescue.org/2018/09/11/destringing-pigeons-...

http://nycprc.org/StringRemoval.html

https://www.stringfootpigeon.com/

They could have any level of sensitivity in their feet and still lose one, not sure if there is any connection between the two.

Attacks from cats and rats, most likely.

> If you’ve ever chewed on a chicken foot,

What?

Chicken feet are cooked and eaten in many countries https://en.wikipedia.org/wiki/Chicken_feet

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