Many birds use a flight mode called undulating or flap-gliding flight, where they alternate
between flapping and gliding phases, while only a few bats make use of such a flight mode.
Among birds, flap-gliding is commonly used by medium to large species, where it is
regarded to have a lower energetic cost than continuously flapping flight. Here, we introduce
a novel model for estimating the energetic flight economy of flap-gliding animals, by
determining the lift-to-drag ratio for flap-gliding based on empirical lift-to-drag ratio estimates …