View From The Shed by Volunteer Shaun - WHY DON'T DUCKS FREEZE?

WHY DON’T DUCKS FREEZE?

You might have noticed that we’ve had some interesting weather over the last few weeks. It’s been what I would call a ‘proper’ winter with snow that doesn’t just fall overnight then disappear by lunchtime the next day. It’s actually settled, frozen and stayed around for a week or more, causing disruption to travel journeys and nature reserve opening times alike. Sorry about that last one but safety first, always. Those paths have been downright treacherous, as my face found out when I landed on it while seeing how slippery Old Moor’s paths were. I was checking on customer safety while neglecting my own. Ouch.

And it wasn’t just me that fell. The temperature plummeted to well below freezing for a while here, not the seven or eight degrees that the forecasters tell me is “normal for a 21st century winter”. So I did the sensible thing and went home to my nice warm sofa with a good book and an even better glass of something warming and ‘medicinal’. I’m retired so I’m still technically on my Christmas holiday for as long as I want. Surely day drinking is allowed in these circumstances?

It was in one of these contemplative moments that I revisited a question that I’d first asked my dearly departed dad over 50 years ago, back in the days when we only had coal fires to heat us, three television channels and the best entertainment was watching Blue Tits pecking at the frozen cream in glass milk bottles (ask your gran).

“Why don’t ducks freeze when they’re floating on an icy lake?”

Dad immediately did that thing that all good parents do when faced with an annoyingly precocious child who won’t stop asking questions; he said the first thing that came into his mind in the hope that it would shut me up.

“Because they’re used to it.”

Well done, Dad. That answer was perfectly acceptable to Short-Trousered Shaun but Old Man Shaun is a lot more cynical. Dad must have known that there was a lot more to it than that and half a century later I’d come to suspect there was too. 

So how do ducks stay warm? Well there isn’t just one reason but several complementary ones and they all work together to keep Mrs Quacky and her quieter mate toasty whatever the elements throw at them.

Firstly they have an excellent system of waterproofing. If you’ve ever been for a wet walk in leaking boots then you’ll appreciate the value of waterproofing. Every part of your body feels colder and is more prone to environmental damage when it gets wet. It’s the same for ducks, which is why they spend a huge amount of time preening themselves. They produce a fatty, waxy substance called preen oil from their uropygial gland located near their tail. Using their beak, they spread this over their entire body. Whilst preening they also straighten their feathers and ‘zip’ them together, as the edge of each feather interlocks with its neighbour. In this way the duck produces a completely waterproof covering, almost like a waxed jacket.  

Beneath the strong, waterproof, outer feathers lies another feather layer. These inner down feathers are incredibly soft and fluffy, designed specifically to trap warm air between the outer contour feathers and the bird’s skin. This keeps the heat in and also aids buoyancy, which is very handy for ducks. If you see a very young chick that looks all warm and fluffy, that’s because the first feathers to grow are these down feathers. Your duvet might even be filled with them. That gives you an idea of how well they keep the heat in. They’re good on my bed so imagine how warm you’d be if your entire skin was covered in down. That helps to explain why a duck’s normal internal temperature is approximately 41 degrees celsius compared to a person’s average 37 degrees. I don't want to know how they measure it in ducks but in this case I’ll simply trust the scientists. 

And there’s even more cold protection happening beneath the skin. Ducks are, as anyone who’s ever cooked one will know, incredibly fatty creatures and that thick layer of fat under their skin goes even further towards insulating them against the icy weather. I may use that as an excuse myself. “I’m not fat, I’m well insulated”.

There’s one more trick going on within a duck's body to help regulate its temperature but for this I’m going to have to get a bit technical. I’m not a biologist but it's a relatively simple concept to grasp. Hold on tight, here comes the science bit.

Even I know that blood gets pumped through a creature’s body via thick arteries and returns to the heart through much thinner veins. The outward-bound blood is warm, having travelled from the body’s literal and figurative heart but by the time it comes back it’s much cooler, having been exposed to the extremities. And this is where it gets clever. The veins run right alongside the arteries with a very thin wall between them, so the colder returning blood is actually warmed up by the arterial blood flowing the other way and the core body isn’t chilled by it coming back. This is called countercurrent heat exchange and it is so efficient that just five percent of body heat is lost through a duck’s feet, even if it’s standing on thick ice. Of course it’s not perfect. No system is. British ducks aren’t made to withstand really harsh conditions for a long time so frostbite is a real possibility once the temperature drops below minus seven degrees for a prolonged period. The bird’s heart rate is so fast though that there isn’t really time for the blood in its feet to cool too much before it returns to the body. And if it gets really bad the birds are masters of balance. They can stand on one leg for hours on end, retracting the other into their downy belly feathers for warmth. Once one foot gets too cold for comfort they simply switch it for the other, alternating the heating process.

So that, in a nutshell, is why ducks don’t freeze in sub-zero conditions. I only wish I could have explained it to my dear old dad.