Watched the big wing birds fly overhead without flapping wings? Looked like a mystery to me. At least they would have flapped a few times after a while to maintain altitude, which they seemingly never did as long as I watched.
New study says that that's the norm. The largest hovering bird in the world weights 15 kg and has a wing span of 3 meter when added both sides together.
It only flaps wings when taking off. And was watched to hover in the air for 5 hours straight covering 150 km and not once flapping its wings.
Talk about design and aerodynamics.
https://www.theguardian.com/environment/2020/jul/13/andean-condor-fly-without-flapping-wings-flight-bird