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Credit: Chris 73

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.