Specialized landing maneuvers in Spix's disk-winged bats (Thyroptera tricolor) reveal linkage between roosting ecology and landing biomechanics

Abstract

Disk-winged bats (Thyroptera spp.) are the only mammals that use suction to cling to smooth surfaces, having evolved suction cups at the bases of the thumbs and feet that facilitate attachment to specialized roosts: the protective funnels of ephemeral furled leaves. We predicted that this combination of specialized morphology and roosting ecology is coupled with concomitantly specialized landing maneuvers. We tested this prediction by investigating landings in Thyroptera tricolor using high-speed videography and a force-measuring landing pad disguised within a furled leaf analogue. We found that their landing maneuvers are distinct among all bats observed to date. Landings comprised three phases: 1) approach, 2) ballistic descent, and 3) adhesion. During approach, bats adjusted trajectory until centered in front of and above the landing site, typically the leaf's protruding apex. Bats initiated ballistic descent by arresting the wingbeat cycle and tucking their wings to descend toward the leaf, simultaneously extending the thumb-disks cranially. Adhesion commenced when the thumb-disks contacted the landing site. Significant body reorientation occurred only during adhesion, and only after contact, when the thumb-disks acted as fulcra about which the bats pitched 75.02±26.17° (mean±s.d.) to swing the foot-disks into contact. Landings imposed 6.98±1.89 bodyweights of peak impact force. These landing mechanics are likely influenced by the orientation, spatial constraints, and compliance of furled leaf roosts. Roosting ecology influences critical aspects of bat biology, and taken as a case-study, this work suggests that roosting habits and landing mechanics could be functionally linked across bats.