Birds fly at tens of thousands of metres high. Ice forms on the wings of planes at this altitude, so why don’t the birds freeze?

Birds can sometimes reach astonishingly high altitudes. The record is a massive 11,278 metres by a Rüppell’s vulture that collided with an aircraft. The resulting “snarge” – that is to say, the bird’s remains – left on the plane provided robust evidence.

Birds almost certainly don’t experience icing while flying at altitude for three reasons.

First, birds normally maintain their body temperature at about 40 to 41°C, higher than that of mammals. Flying is such hard work that it probably uses about twice as much oxygen per unit of time as running does, so birds are plenty warm as they fly about, even at very high altitudes.

Second, birds’ feathers are a fascinating evolutionary adaptation to not only flight, but also life outdoors. As well as being beautiful and providing lift and trim in flight, feathers keep birds warm and waterproof. They do this via complex microstructures that trap air and repel water. Birds also spend a lot of time preening their feathers to coat them in a layer of “preen oil”.

The content of preen oil varies between bird species, but mainly contains monoester waxes and triglycerides, which are oily and repel water. Next time you spot a bird in the rain, marvel at how raindrops sit on top of its feathers as beads, rather than making the bird wet. That is preen oil at work. Indeed, one of the solutions used to prevent accidents in aircraft flying through icing conditions is to use hydrophobic surfaces.  ( Lucy Hawkes, University of Exeter, Devon, UK)

My comment: just thought you might be interested.  In fact, there are all sorts of obscure questions you have probably never thought of asking.  I will try to make it my business to find occasional obscure and useless facts from time to time and bring them to your notice.  It’s a way of momentarily focusing on anything except  the dismal news.

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