I wonder if, even if the bird doesn't take the boat for a long distance (i.e. cutting off time spent flapping), just having the ability to rest and recover in the middle of the ocean provides it the boost to keep on going. Or some safety factor. Just like Midway Atoll for us...hah.
This is the amazing evolutionary advantage of albatrosses; they fly using a technique called dynamic soaring, which allows them to extract kinetic energy from the wind. It's the same concept really as moving sidewalks in the airport, so their gliding heartrate is about the same as when they're resting on the beach or water. This is what allows them to fly such massive distances across the ocean!
> Where's the gradient? Do they fly at the boundary between different wind speeds?
At the surface of the water, windspeed is lower than at higher altitudes, so that's where the gradient is. If you watch an albatross soaring over water, you'll watch it dive so low its wingtip touches the water surface, and then it'll climb in altitude, before turning to dive again. Here's a good diagram of the whole process: https://www.researchgate.net/profile/Sameh-Eisa/publication/...
