title: Flapping tail membrane in bats produces potentially important thrust during horizontal takeoffs and very slow flight.
abstract: Historically, studies concerning bat flight have focused primarily on the wings. By analyzing high-speed video taken on 48 individuals of five species of vespertilionid bats, we show that the capacity to flap the tail-membrane (uropatagium) in order to generate thrust and lift during takeoffs and minimal-speed flight (<1 m (s-1)) was largely underestimated. Indeed, bats flapped the tail-membrane by extensive dorso-ventral fanning motions covering as much as 135 degrees of arc consistent with thrust generation by air displacement. The degree of dorsal extension of the tail-membrane, and thus the potential amount of thrust generated during platform launches, was significantly correlated with body mass (P = 0.02). Adduction of the hind limbs during upstrokes collapsed the tail-membrane thereby reducing its surface area and minimizing negative lift forces. Abduction of the hind limbs during the downstroke fully expanded the tail-membrane as it was swept ventrally. The flapping kinematics of the tail-membrane is thus consistent with expectations for an airfoil. Timing offsets between the wings and tail-membrane during downstrokes was as much as 50%, suggesting that the tail-membrane was providing thrust and perhaps lift when the wings were retracting through the upstoke phase of the wing-beat cycle. The extent to which the tail-membrane was used during takeoffs differed significantly among four vespertilionid species (P = 0.01) and aligned with predictions derived from bat ecomorphology. The extensive fanning motion of the tail membrane by vespertilionid bats has not been reported for other flying vertebrates.
authors.affiliation: School of Biological Sciences, University of Northern Colorado, Greeley, Colorado, United States of America. rick.adams@unco.edu
authors.forename: Rick A
authors.initials: RA
authors.lastname: Adams
authors.forename: Emily R
authors.initials: ER
authors.lastname: Snode
authors.forename: Jason B
authors.initials: JB
authors.lastname: Shaw
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002685:Chiroptera / Q000033:anatomy & histology / Q000502:physiology*; D005426:Flight, Animal; D008954:Models, Biological; D009038:Motion; D009991:Oscillometry; D013045:Species Specificity; D013997:Time Factors; D014741:Video Recording; D014921:Wings, Animal / Q000033:anatomy & histology