About Thyroptera tricolor Spix, 1823
Spix's disk-winged bat, Thyroptera tricolor, has a white or pale yellow underbelly and a dorsal surface ranging from reddish-brown to black. In one survey of the species, females had an average forearm length of 37 millimetres (1.5 in), and males had an average forearm length of 36 millimetres (1.4 in). Adults weigh around 4 grams (0.14 oz). Unlike most bats, T. tricolor clings head-up to its roost. This head-up roosting behavior is seen in six total bat species from two genera: Thyroptera (the disk-winged bats) and Myzopoda (the sucker-footed bats). These two groups independently evolved similar adhesive traits through parallel evolution, but their adhesive anatomy functions differently. Disk-winged bats roost inside rolled leaf buds with an opening at the top, clinging head-up to the smooth ventral inner surfaces of these leaves. Heliconia and Calathea are plant species with this leaf morphology. This roosting method is thought to let the bat escape quickly if it is disturbed. The adhesive disks of T. tricolor are shaped like concave cups, supported by an internal cartilaginous plate. The flexor pollicis brevis muscle attaches to this plate; when the muscle contracts, it changes the overall shape of the disk to create suction. To keep the disk functional, the bat frequently grooms it by licking. The disks also have many sweat glands that keep their surface moist. The Madagascar sucker-footed bat (Myzopoda aurita) has similar-looking sucker anatomy, but creates suction through a different method. It uses its flexor muscle to change the disk's shape only when detaching from a surface, and uses sweat lubrication for wet adhesion as its primary attachment mechanism instead of suction. Unlike T. tricolor, which can cling at any angle, M. aurita can only attach head-up. M. aurita can also make contact with both its adhesive organ and its thumb claw at the same time, which T. tricolor cannot. This difference may be caused by variation in the anatomy of muscle insertions and the resulting movements they allow. Spix's disk-winged bat is distributed across Belize, Bolivia, Brazil, Colombia, Costa Rica, Ecuador, French Guiana, Guatemala, Guyana, Honduras, Mexico, Panama, Peru, Suriname, Trinidad, Tobago, and Venezuela. It has a patchy distribution but an extremely wide overall range, and the International Union for Conservation of Nature (IUCN) lists it as a least-concern species. The abundance of this species may be limited by the availability of its preferred roosting sites. Unlike other bat species that can gather in large groups, hanging head-down by their toes from cave ceilings and hollow trees, T. tricolor is adapted to roost in furled leaves, so its population size is restricted by the abundance of plants that produce this leaf structure.
