Hummingbirds & bats in Science Advances
Evolution is miraculous,
both hummingbirds and nectar bats evolved to hover in front of flowers to drink
nectar and eat pollen. How do they hover and do they hover differently? Rivers
Ingersoll and visiting student Lucas Haizmann published their answer in Science
Advances. Comparing 100+ individuals across 17 hummingbird species, 2 nectar
bat species and 1 fruit bat species in the same Costa Rican ecosystem, they discovered
that the 17 hummingbird species converged on hovering the same. Hummingbirds
also hover aerodynamically more efficient, supporting their body weight both on
the downstroke and upstroke. Bats have a less effective upstroke, for which they
make up by making better use of their downstroke with their disproportionally
large wing. The larger wings of bats reduces the energy needed to generate
aerodynamic force, mitigating their reduced aerodynamic efficiency.
Surprisingly, the net outcome is that hummingbirds and nectar bats need the
same amount of power to hover per kg bodyweight. The study also shows nectar
bats are better at supporting their body weight during the upstroke than fruit
bats – by inverting their wing further like hummingbirds do. Finally, the study
showed that regardless of flower angle, both specialist and generalist hummingbirds
generate the same aerodynamic force to support their body weight. They accommodate
different flower angles with their supple necks and tails while flapping their
wings the same. The findings will help inspire more effective hummingbird and
bat inspired robots: To hover efficiently, engineers should copy hummingbirds.
If the robot is not as effective as hoped, they can learn from bats and simply increasing
the size of the wing to reduce the energetic cost of hovering flight.