What does it take to make a reindeer fly?

This blog is about 'Furahan Biology and Allied Matters', and today we will stretch the 'allied matters' a bit, to produce this special Christmas post. Somewhere in Speculative Biology there must be a place to think about re-engineering mythological life forms, which is what this post is about.

The starting condition is simple. Thanks to globalisation, a most unusual subspecies of reindeer (Rangifer tarandus) has spread widely from its original area, so it can now be observed in skies over many parts of the world. In the skies? Yes, because these reindeer fly.       

It is not clear whether these reindeer can fly in their natural state, as they are only observed to do so when tethered to sleighs. This is slightly worrying, but even so, the force that keeps them in the air must be magic, as the reindeer lack any observable physical means to provide lift. While magic is a potent force in the imagination, in the real world it is noticeably difficult to acquire, so we need a more pragmatic approach. 

What would it take to make a reindeer fly in the real world? And I mean 'fly', not hurtling it through the air by strapping a jetpack to its back or using a large catapult. No, it must fly though biological means. The first problem is that reindeer have no wings, so we will have to use advanced creative bioengineering and splice in some wings. Done! That was quick...

Reindeer weigh around 100 kg, if we average estimates of male and female weight. But even these brand-new wings won’t make a 100-kg reindeer fly. And don't you start objecting that some pterosaurs weighed more than 100 kg and could still fly. We could in fact probably re-engineer the flying reindeer to achieve pterosaur-like mass, but the result would definitely look a lot like a pterosaur, and it should look like a reindeer, right?
 
Where was I? Oh yes, the 100 kg mass is a problem. Why? Well, take a 0.6 kg pigeon with a 70 cm wingspan. If you double its length, width and height, you get a wingspan of 140 cm and it will weigh 8 times the original weight. That factor 8 represents doubling of all three of length, width and height, so it is doubling to the third power (2 to the power of 3). By the way, for more on basic scaling of animals, see these posts here and here.

The problem is that lift is proportional to wing area, and area is proportional to the square of length. Doubling the pigeon's size makes the wing area four times larger, but that four times larger wing must carry eight times the weight. That won’t fly. (Sorry for that one.) We can make the wings extra large to compensate for the larger weight, but that will also increase weight. As explained in another post, at some point of increasing body size the wings can no longer carry the body.  

The obvious solution is to shrink the reindeer until it weighs as much as something that can fly. Say a rather massive goose at about 5 kg. Some calculations reveal that the reindeer's length should then be 25-30% of the original length of 180 cm.

To allow room for massive wing muscles, everything else must be reduced in weight: to decrease gut size it needs a new diet, mostly sugar; we can then also abolish the teeth, because it doesn't need them and won't get caries. We'll give it slender legs, tiny light hooves and fluffy hair. You will probably insist on antlers, so antlers can stay, but they will be much reduced. We can splice some red bioluminescence into its nose, to put the cherry on the cake.    

Done! A realistic flying reindeer! 

Click to enlarge; copyright Gert van Dijk & Roelien Bastiaanse

 

Happy holidays!