Spix’s disk—winged bat (Thyroptera tricolor), is an insectivorous ^[1] species of bat in the Thyropteridae family ^[2]. Although this species is unevenly dispersed, it is widespread and is therefore considered as having a “least concern” status on the conservation list ^[3]. The most prominent anatomical feature of this bat, separating it from other bats, is the presence of disks on its thumbs and hind feet. These circular disks act as suction cups, allowing the bats to cling onto and move along smooth surfaces ^[2].

Distribution and Habitat

T. tricolor can be found in South America, in the Neotropical region and is native to the countries of Venezuela, Tobago, Trinidad, Suriname, Peru, Panama, Mexico, Guyana, Guatemala, Honduras, French Guiana, Costa Rica, Ecuador, Colombia, Brazil, Belize, and Bolivia ^[3].

Species abundance of the bat in its native Neotropical land may be limited by the availability of roosting sites. Whereas other species of bats are capable of aggregating in large numbers, hanging head—down by their toes from cave ceilings and hollow trees, T. tricolor is adapted to roosting in, and therefore limited by the abundance, or lack thereof, of furled leaves in its habitat ^[2]

Characteristics

General Anatomy, Behavior, and Diet

Spix’s disk-winged bat possesses a white, or pale yellow underbelly and a reddish brown to black dorsal surface ^[2]. The bats possessed an average forearm length of 36.8 mm and 35.57 mm for females and males, respectively. The average weight of this species of bat is approximately 4.02 grams, and their colonies maintain a sex ratio of 1:1^[1]. When studied, these bats did in fact display social organization, as well as roosting aggregation, with the mean colony size consisting of six members. Regardless of the bat’s specialized morphology, it is still able to maneuver in flight, with agility, as it circles the mouth of furled leaves which could potentially serve as a roosting location. T. tricolor has not been observed to fly at heights greater than 3 to 5 meters above the forest floor^[1]. As previously mentioned, the bat’s diet consists of insects, and estimates indicate that a given individual may consume up to 0.8 grams of insects a night ^[2].

Specialized Anatomy: Disks

Unlike most bats, T. tricolor clings head—up from its roost. This phenomenon is observed in six bat species which occur among two families, Thyroptera spp. and Myzopoda spp. The former are known as disk—winged, whereas the latter as sucker—footed. Although the two families represent an occurrence of parallel evolution, the manner in which their unique adhesive anatomy is utilized differs morphologically^[4].

These bats cling head—up to the smooth inner, ventral surfaces of the rolled up leaves with openings at the top, of Heliconia, sometimes Calathea, as well as other similar plants, using their adhesive disks.^[1]. This manner of roosting is said to facilitate rapid escape in the event of a potential disturbance^[5]. The bat’s disks take the shape of concave cups, and are supported by an internal cartilaginous plate. An extrinsic muscle, the flexor pollicis brevis, attaches to the plate, such that contraction of the muscle alters overall disc shape, ^[4], creating suction. In order to maintain the integrity of the disk, T. tricolor is observed to groom the disk, by frequently licking it. In addition to that, the disk contains sweat glands which discharge onto its peripheries, thereby maintaining it in a constantly moist condition ^[2].

Contrary to M. aurita, T. tricolor uses the insertion of the flexor pollicis brevis to alter disk shape and adhere to a smooth surface, rather than detach from it. In addition to that, the bat uses suction, rather than wet adhesion (via sweat—lubricated disks) as the major mechanism for clinging. When unable to create a seal for suction, wet adhesion is in fact used, but only produces a very weak adhesion. Furthermore, in contrast to the sucker—footed bat, Spix’s disk—winged bat only roosts head—up, but can cling to a smooth surface at any angle, whereas the former can only attach head—up. As such, it is of note that M. aurita can concurrently make contact with both its adhesive organ and thumb claw, whereas T. tricolor cannot. This may be due to the difference in morphological features between the bats^[4] due to the varied muscular insertions and the different functions they bring about.

References

1. ^ ^{a b c d} Findley, James S., and Don E. Wilson. "Observations on the Neotropical Disk-Winged Bat, Thyroptera Tricolor." Journal of Mammalogy 55.3 (1974): 562-71. Print
2. ^ ^{a b c d e f} Wilson, D.E., and Findley, J.S. 1977. Thyroptera tricolor. Mamm. Species No. 71. pp. 1–3.
3. ^ ^{a b} "Thyroptera Tricolor." IUCNRedList.org. The IUCN Red List of Threatened Species, 2011. Web. 17 Mar. 2012. http://www.iucnredlist.org/apps/redlist/details/21879/0
4. ^ ^{a b c} Riskin, Daniel K., and Paul A. Racey. "How Do Sucker-footed Bats Hold On, and Why Do They Roost Head-up?" Biological Journal of the Linnean Society 99.2 (2010): 233-40. Print
5. ^ Göpfert MC, Wasserthal LT. 1995. Notes on echolocation calls, food and roosting behaviour of the Old World sucker footed bat Myzopoda aurita (Chiroptera, Myzopodidae). Zeitschrift für Säugetierkunde 60: 1–8

References

• Chiroptera Specialist Group 1996. Thyroptera tricolor. 2008 IUCN Red List of Threatened Species. Downloaded on 26 October 2008.
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