Descending bird in a turn; birds facing the wind on the waves
How a bird descends turning; why birds keep their front to wind and water
Continuing his notes on the flight of birds, Leonardo remarks that, moving slowly and with the body bent, a bird descends while turning to one side. A second note, beside a drawing of three birds settled on the waves, explains that birds driven by water or wind keep their front toward the oncoming current, so that the water or wind cannot force its way from the feather tips back to their roots; the feathers press together and the bird stays drier and warmer.
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A bird descends turning slowly to one side
Leonardo observes that, moving slowly and with the body bent, the bird descends while turning toward that side, a short note on how attitude governs a banking descent.
Why birds keep their front against wind and water
Birds pushed by water or wind hold their front against the oncoming current so that it cannot penetrate from the tips toward the base of the feathers; instead each feather is pressed against the next, keeping the bird drier and warmer.