Seven swans are swimming

Seven swans went swimming, according to the song. And some people also enjoy a cold dip at Christmas. Caroline Steel went for a swim in the name of science, and Chris Smith heard from Eleanor Drinkwater how birds avoid getting cold feet...

Chris - So far we’ve covered 6 of the 12 days of Christmas… Now it’s time for the 7th...

Everyone sings: on the seventh day of Christmas my true love gave to me, seven swans a swimming, six geese a laying, five gold rings, four calling birds, three French hens, two turtle doves, and a partridge in a pear tree.

Chris - Even at this time of year when it’s freezing here in Cambridge, it’s common to see swans swimming down the River Cam. But there are also people who enjoy swimming outdoors at this time of year. So we sent producer Caroline Steel to the pool in Tooting, London, to break the ice - almost literally - and take a dip with cold water enthusiast Alex Harper...

Alex - You can imagine being in a spar and you go in a plunge pool and you get a rush from it.  Well this is exactly the same kind of rush. It’s definitely getting cold, and getting warm in the sauna and getting cold again. It’s a huge endorphin release, or certainly a high buzz.

Caroline - Given that I don't think I’ve actually swum in about six months, what do you think will happen to me - how am I going to feel?

Alex - Well, we’ll walk in. but it’s up to you, you can walk or jump. I suggest walking down the steps and you will feel cold. It’s cold water and there’s no getting away from your skin will cool down, and mildly painful, but, honestly, it is mental. Physically you'll be fine, it’s the mental anguish of feeling cold, feeling uncomfortable.

Caroline - Okay. So before you hear my reaction, I just want to emphasise that the water was less than four degrees celsius. Actually, it has frozen over just three days earlier. Okay, so excuses over it’s time to jump in…

Okay, so I’m as ready as I can possibly, physically be.

Alex - Excellent.

Caroline - Is your plan to go in first and…

Alex - Do you want to go in first? Do you want to go in? And we go… no hanging around. Okay, so just get in.

Caroline::. So obviously, it was pretty cold. My skin cooled down straight away and, as my blood vessels constricted, I went really pale. But by the second length my skin went numb and it became marginally bearable.

Alex - Excellent. How was it?

Caroline - I feel like I’m not completely with it. But I enjoyed…

Alex - You did it. You finished. Well done!

Caroline - I enjoyed the second leg.

Alex - You could have done two more, couldn’t you?

Caroline - Phew, phew. Oh my Gosh!!

I’m on a beach, it’s boiling, it’s so hot that I actually want to go in the sea. I need to put on more sunscreen, I’m burning. It’s boiling… it’s boiling.  Okay, so as much as I wanted to believe that, it didn't really help me warm up. So here’s cold water enthusiast and doctor, Martin Thimbar...

Martin - Well, the dodgy thing is you get a warm glow. You often get a feeling of a warm glow after you’ve been in there, which is deceptive because, actually, it’s going to mean you lose quite a lot the heat. And so the thing to do with anyone who's a bit cold and that is put layers on. People sometimes make the mistake when they’re really quite cold of going into a hot shower and standing up. That doesn’t warm your core quickly enough but what it does do is it encourages your blood vessels on the side to dilate, and you blood pressure can drop down. So when people faint, they can faint from being cold and then having a hot shower. The best thing to do is just sit quietly and put layers on.     

Chris - Good advice. Eleanor - How do swans manage to swim in 3 degrees C water?

Eleanor - They have an amazing system called the countercurrent exchange system in that their veins and arteries are very, very close together - those going down to the foot and those going away from the foot. So you have this amazing system where the warm blood from the body gets cooled by the blood going in the opposite direction, so when the blood gets to the foot it’s already cold so the bird doesn’t lose that much heat.

Chris - Neat. So by basically pumping hot blood out of the body and passing it very close to cold blood coming back, the cold blood grabs all the heat from the hot blood so by the time it gets to the foot it’s so cold it’s not got much heat to lose. So it stays as cold as the foot was without the bird actually losing any energy?

Eleanor - Yeah, that’s exactly right.