…from Bats Have an Aerodynamic Edge Over Birds, Study Shows, National Geographic:
"A bat caught in mid-flight in a fog chamber reveals the unique flapping mechanisms that differentiates mammal and bird wings. The arrows represent air movement produced by air motion—and show that, unlike birds that generate lift only when flapping downward, bats flex their wings to create thrust both on their downstrokes and upstrokes."

A fun photo, posted here to remind readers to check the National Geographic headlines linked on the left side of this page. Enjoy!