A reader question today! Dolores asks: Would the body heat of a modest mixed gathering of water birds (gulls, ducks etc) melt ice at the edges of a pond?
The answer to this depends on context. We can start by establishing some extreme end-points: one duck at the edge of a huge lake in way-below-freezing weather would not be able to melt any ice.
Twenty ducks splashing around spiritedly in a kiddie pool with the barest skin of ice in weather just at the freezing point would probably, if you waited long enough, cause the ice to melt.
Between our two endpoints are more “normal” circumstances: a group of waterbirds hanging out at a pond. Could they melt any ice?
There are several reasons why your gut feeling should be telling you that the answer is “no.” First is the fact that we often see waterbirds standing on ice.
Of course, just because they’re standing on the ice doesn’t mean they aren’t melting it. Maybe they melt little footprints in the ice and then move to another patch of ice.
If you stood on ice in bare feet, you would melt the ice. If you tried to do that for a long time, you would get frostbite and tissue damage and then you would not have working feet anymore. To melt ice, you have to put enough energy into it to raise its temperature above freezing, plus some bonus energy to get it over the phase change from solid ice to liquid water. Because water has a very high specific heat—i.e., it takes a lot of energy to raise its temperature—melting ice requires a lot of energy. For an animal to melt ice with its feet, all of that energy would have to come from the animal; and unless it was a very small amount of ice and a very big animal, that animal would get very cold.
Ducks don’t melt the ice they stand on. Duck feet are designed to leak as little heat into their surroundings as possible—they use counter-current exchange to accomplish this—and this is essential, because if they spent winters regularly losing enough energy to melt ice, they would die.
So that’s feet; but there’s more to waterbirds than just feet. They put their whole lower bodies in the water.
Sometimes they put even more in the water.
Could the body heat from their bellies/heads/etc., plus their feet, warm up water and melt ice? Well, technically, yes: ducks do lose body heat while in the water (about 20% more heat is lost from swimming ducklings than ducklings standing on land [Van Sant & Bakken 2006]), so they are warming up the water a tiny bit; and given a small enough amount of water and ice, and enough ducks, you could probably melt some ice.
But in any natural environment, the amount of heat the birds lose will be too little to affect ice to a visible degree. Birds can’t afford to lose much heat in the winter, and they have evolved very effective insulators in their feathers. Ducklings lose almost the same amount of heat through their feathers to the water as they do to the air—which is pretty amazing, considering how cold water can suck heat away!
The body heat from a normal-sized group of waterbirds would not be able to melt ice in any realistic natural setting.
It is possible that the presence of waterbirds might either prevent ice formation or speed its disappearance in a different way. Birds don’t just sit in water, after all.
They paddle, and dive, and splash around. Ice can’t form in water that is constantly moving, so a flock of active birds could potentially delay part of a pond from freezing over. Too, turbulence caused by ducks could stir up the warmer bottom layer of water, bringing it into more contact with the surface ice and perhaps very slightly speeding up the melting of the ice. So maybe a flock of waterbirds could cause a small decrease the amount of ice on a pond.
Of course, none of this works if the ducks decide to hang out on land…
Van Sant MJ, Bakken GS. 2006. Thermoregulation on the air-water interface – II: Foot conductance, activity metabolism and a two-dimensional heat transfer model. Journal of Thermal Biology 31:491-500.
The first time I saw Goldeneyes swimming around the ice In the river during early winter, I thot they had lost their minds! They seemed quite oblivious.
It’s always amazing to see ducks hanging out in extremely cold water, even when you’ve come to expect it of them. But then I suppose penguins would think the ducks are wimps, so it’s all relative.
The Northern Pintail is stunning, especially the blue foot. What’s the black spiky feather at the back: just a feather in shadow? These photos look great enlarged!
The feather is just in shadow, yes. And the bright foot is actually a bright band on the foot – the foot itself is sort of pale blue-grey. (The banded ducks are all at Lincoln Park Zoo.) But I do think she’s very pretty!
Totally fascinating – a thoroughly entertaining analysis! Thanks so much. Fabulous photos.
Thanks Dolores! I appreciate the interesting question, it was fun to look into. And I’m always looking for an excuse to use my duck photos :-)
Great explanation. I think the greatest contribution they make to melting is what you mentioned last. They keep the water in motion which generates kinetic energy bringing up the temperature of the water.
Thanks! I agree that that is probably where any waterbird ice-melting effect comes from. It’s not so much kinetic energy making the water *warmer* – just try warming up your iced tea by stirring it and see how far you get – as making it harder for the water at the same temperature to freeze. If you put a thermometer in the water, the temp wouldn’t have changed; but the kinetic energy prevents the water from forming all the bonds it needs to become an ice crystal.
I like that there is a journal of thermal biology. Any idea how many calories a duck consumes in a day? That would set an upper limit on the amount of heat that could go towards melting ice. A human consumes about 2000 kcal = 8.4 million Joules of energy a day. The latent heat of fusion of water is 334 J/g. So, if a human put all its energy in a day into melting ice and the ice was just below 0 degrees C so that it is just about to melt, a human could melt 25 kg of ice a day, which comes out to 25 L (6.6 gallons) of water. Incidentally, the average power required to run a human is about 100 W – about the same as a the power of a high-powered light bulb, or a tenth the power of a toaster. Humans are amazingly efficient!
Thanks for doing the calculations! A human melting 6.6 gallons of ice is kind of impressive – but I don’t think the human would come out of it in very good shape…
I’m having trouble finding values for energy consumption, but energy expenditure in Tufted Ducks varied between ~400 and ~1400 kJ per day. (Higher energy expenditure was related to low temperatures, down to about 3-5 degrees C; no data on 0 degrees C). Tufted Ducks dive to feed on mussels, so they lose a lot of heat to the water relative to other ducks since they’re constantly submerging their entire bodies in water. Following your example, the 1400 kJ would let the duck melt a maximum of ~4.2 kg of ice per day, or 1.1 gallons. (Except the duck would be dead if it did that because it would have no energy to keep itself alive…)
Reference: Tufted Duck data is from de Leeuw et al. 1999. Wintering Tufted Ducks Aythya fuligula Diving for Zebra Mussels Dreissena polymorpha Balance Feeding Costs within Narrow Margins of Their Energy Budget. Journal of Avian Biology 30(2):182-192.