How is a reindeer's nose like a condensing boiler?

I am sure it has not escaped your notice that the weather recently has been unusually cold for the time of year. How have you been keeping warm? In our house we have turned down the heating a bit, because with the energy shortage due to the war in Ukraine it is very important to reduce our energy consumption as much as possible, to keep the prices down. (Even with the price guarantee, we will pay for it eventually, probably through our taxes.) As always it is worth taking a look at the natural world for tips. Since it is Christmas, reindeer are a good start. How do reindeer keep warm?

Most obviously, reindeer have tremendously thick fur coats. I don't know if you have ever picked up a fur coat; if you have you will know they are normally quite heavy. However the reindeer fur is hollow, like a hollow fibre quilt. This makes it lighter to carry and more insulating. Feathers are also very good insulators as they also trap air - helping to keep penguins warm. My quilted down coat is very light and warm too. 

Cross section of a hair on a reindeer. Image from [1]

Penguins famously huddle together to protect each other from the wind and share their body heat. Other animals such as voles huddle together in a nest. On a cold evening I like to huddle with my beloved on the sofa. If you don't have a beloved, a hot water bottle or a heated jacket are a good substitute, at least in this respect. Unfortunately they will not make tea. However, both provide heat very close to the body, like a warm cuddle.

Emperor penguins in a huddle. Image from BirdWatching 

Animals that need to keep warm are often rounded in shape. The bits that stick out, such as legs have a large surface for heat loss. To keep the legs functioning without losing heat unnecessarily, animals like the reindeer use blood vessels as countercurrent heat exchangers. The blood flowing down to the legs gives up heat to the blood coming back up. The feet can be as much as 30°C colder than the main body of the reindeer. Many birds, especially water birds, use the same technique on their legs while whales and seals have a similar mechanism to reduce heat loss from the tail.

Countercurrent blood flow keeps the reindeer's feet and nose warm. Image from Back Yard Biology 

Reindeer have the same sort of system in their noses. This is especially important as when we breathe out through our nose we lose heat from our lungs. The reindeer's nose has a lot of blood vessels that absorb heat from the warm air. The reindeer can control the blood flow to retain more or less heat.

We do not have this capability and we have not invented clothes to do it either. However, our houses can use heat exchangers to reduce heat loss. There are several possibilities but the most common one is the gas boiler. In a modern gas boiler the hot flue gases are used to warm up cool water that has been returned from the radiators. Also, both the boiler flue gas and the reindeer's breath are heavy with moisture for exactly the same reason - the water has been generated by oxidising fuel (fat/methane gas) and the hydrogen in the fuel becomes water. When this moist air is cooled the steam condenses and this returns a lot of extra heat. You will not see steam condensing in the breath of a reindeer as we do from our own because it is already condensed in the nose. So the reindeer's nose is like the condensing heat exchanger in your gas boiler.

I hope you have a wonderful break - we look forward to seeing you again in the new year.

[1] Superb winter fur insulation in the small Siberian musk deer (Moschus moschiferus)

Arnoldus Blix, Marina Vladimirovna Kholodova, Edward Messelt and Nicholas Tyler (2015) in Rangifier