> I doubt our flying machines are anywhere near as energy efficient as birds

This kind of nerd sniped me, so I looked into it and turns out no, planes are more efficient than birds!

You have to look at the energy spent for moving a fixed mass over a fixed distance and for the most efficient birds I looked into, that’s about 300g of fat burned for 300g of “dry weight” for a trip of ~11,000km. (bar-tailed godwits)

For a plane that’s roughly 80 tonnes of kerosene for 170 tonnes dry weight on a similar distance (787). Energy density of fat and kerosene are actually pretty close so you can just look at the kg of fuel burned per kg of payload for the trip. For a bird that’s 1kg of fuel per kg transported and for the plane that’s ~0.5kg per kg. So roughly twice as efficient.

So from a pure energy point of view it’d be more efficient to put all the migratory birds in a 787 than letting them fly on their own!