Did some quick maths, it’s roughly 10% for the bird (2W, approx. 4g/day of fat, over 10 days) so not negligible but doesn’t change the full story.

And you could argue the plane also has a baseline metabolism ;)

Haha thanks for the check, I am, tbh, pretty surprised. But it's within the same order of magnitude given the assumptions, which is interesting too.

	▲	nsarrazin 24 minutes ago \| parent [-]
		To be completely fair to the birds, I think a lot of this comes from the fact that what matters for flying efficiency gets better as you size up thanks to the square-cube law: the drag is reduced and the engine efficiency increases. You could not scale down a plane to the size of a bird and match their efficiency. On the other hand you also couldn’t scale a bird to the size of a plane so I guess we can call it even!