Behavior

Disk-winged bats use their suction cups to cling to near-vertical smooth surfaces of the rolled-up leaves inside which they roost. While moving around a roost, neither the feet nor claws touch the smooth leaf surfaces, with the cups alone being responsible for grip. Situated on short stalks, the cups generate sufficient suction to allow captive Thyroptera to move easily and without slippage across a clean pane of glass. The suction is not generated passively; modified sweat glands in the disks produce a sticky secretion and there is also a tendon leading from a cartilaginous plate in the disk to muscles outside it; this helps keep the shape appropriate. A bat will also lick its disks to aid adhesion. Using this combination of suction and wet adhesion, a single disk can support the bat's entire weight. Suction requires constant muscular expenditure to keep the cup in the right shape. This could be energetically demanding over a night's roosting. So, the wet adhesion may be an energy-saving device. Experiments have shown that, in specializing to roosting on smooth surfaces, Thyroptera has lost the ability to roost on rough surfaces (rock, bark) as most bats can and do. The roosting sites protect the tiny bats from the rain and from predators. In captivity, disk-winged bats with no suitable substrate will hang head-up by their thumb-claws, rather than try to suspend themselves from their tiny weak feet. Within the order Chiroptera, the suction cups of Thy-

roptera are the most specialized organs of their kind. Some African bats (Myotis bocagei and Glishropus nanus) also roost in rolled-up banana leaves. The latter has thickened pads at the wrist. These are reported to allow adhesion to the leaf surface. M. bocagei uses its fine sharp claws for attachment to the leaf.

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