While we humans eat a lot, something like 50% of our calories are going to our brains.

I don't think that's right.

This article says that about 20% of an adult human male's resting energy expenditure goes towards supporting the brain's metabolism. Obviously for more active people, the higher denominator of total energy expenditure will mean an even lower percentage of energy being used for the human brain.

Flying is energetically expensive to start doing, but pays off in efficiency once an animal moves a far enough distance. How many calories does a goose need to consume to fly 4000 km, and how does that compare to terrestrial species like deer or wolves?