Kitti's hog-nosed bats

(Craseonycteridae)

Class Mammalia

Order Chiroptera

Suborder Microchiroptera

Family Craseonycteridae

Thumbnail description
World's smallest bat, thickened snout with two crescent shaped nostrils, eyes are minute, ears large with well developed tragus, no external tail, pelage is light buffy brown above, paler below

Size
Head and body 1.3 in, 34 mm; no tail; forearm 0.9 in, 24–25 mm; weight 2.0–2.6 grams

Number of genera, species
1 genus; 1 species

Habitat
Caves in limestone outcrops usually located near rivers, bamboo, deciduous and evergreen forest, paddy and cassava fields, orchards

Conservation status
Endangered

Distribution
Thailand and Myanmar (Burma)

Evolution and systematics

The evolutionary history of Kitti's hog-nosed bat is still unclear and there is no fossil record. It shares morphological characters with two Old World bat families belonging to the superfamily Emballonuroidea (which includes the Rhinopomatidae and Emballonuridae). It has the same dental formula, general skeletal design and skull morphology as the mouse-tailed bats (Rhinopomatidae) but specific traits of the skeleton and arrangement of the premaxillae are closer to the sheath-tailed bats (Emballonuridae). Unlike both families, it lacks a tail and has a more inflated braincase and relatively larger incisors. However, recent molecular evidence suggests that the hog-nosed bat should be included in the superfamily Rhinolophoidea (including the Nycteridae, Megadermatidae, Rhinolophidae, and Hipposideridae), suggesting that it is more closely related to elements of the leaf-nosed bats (Hipposideridae) and particularly the trident roundleaf bat Aselliscus stoliczkanus.

The taxonomy for this species is Craseonycteris thonglongyai Hill, 1974, Kanchanaburi, Thailand.

Physical characteristics

Kitti's hog-nosed bat is so small that it is considered to be the smallest mammal in the world, and for this reason, it is also known as the bumblebee bat. It weighs between 0.7 oz and 0.9 oz (2.0 and 2.6 g). The tail is absent, although there are two caudal vertebrae. There is a large interfemoral membrane but no calcar. The snout is thickened and there are two clearly defined, crescent-shaped, hog-like nostrils. The eyes are minute and largely concealed by hair. The ears are large, with well-defined but rounded tips; they are not connected to one another and each has a well-developed tragus. In males, there is a large glandular swelling on the lower part of the throat; in females it is less developed or absent. The wings are relatively long and broad, their structure similar to those of bats in the superfamily Rhinolophoidea (slit-faced bats, false vampires, horseshoe, and leaf-nosed bats). The hairs on the back are light buffy brown. They are slightly paler on the belly. In the skull, the braincase is inflated, with a prominent sagittal crest and enlarged tympanic bullae. The premaxillae are a unique character of the family. They are not fused with the maxillae but form a separate ring-like structure. There are 28 teeth. There is one

pair of upper and two pairs of lower incisors, one pair of upper and lower canines; one pair of upper and two pairs of lower premolars and three pairs of upper and lower premolars. When hunting, Kitti's hog-nosed bat uses 3.5 ms long multiharmonic constant frequency (CF) search signals with a prominent second harmonic at 73 kHz repeated at around 22 Hz. This can be used to acoustically indentify the bats.

Distribution

The global distribution of Kitti's hog-nosed bat is currently thought to be restricted to two small areas of South-East Asia. In Thailand, it has been recorded in 21 caves, most of which are located in Sai Yok National Park, Kanchanaburi Province with the remainder in adjacent areas on the Kwae Noi (River Kwai). In March 2001, a second population was found in a cave in Mon State, Myanmar (Burma). This represents a range extension of about 155 mi (250 km).

Habitat

Kitti's hog-nosed bat roosts in limestone caves, preferably those with many chambers and domed roofs and located near rivers. In Thailand, the land adjacent to the caves was formerly dry deciduous hardwood forest, with some dry evergreen forest and giant bamboo, but much of the forest is now cleared and given over to agriculture, particularly cassava and kapok plantations and to a lesser extent bananas, corn, and orchards of mango, jackfruit, and lemon. In Myanmar, the hog-nosed bat was found in a cave in a large limestone outcrop in an agricultural area of rice paddy and toddy palms.

Behavior

The bats hide in small holes or in crevices formed by stalactites in caves. Each bat maintains a certain distance from other individuals. In Thailand, the number of individuals in one roosting site varies between 1 and 500, with an average colony size of 100. There is some seasonal movement between caves. They have two brief activity periods, one in the morning and one in the evening. They circle at the cave entrance about one minute before leaving. About 10 minutes after sunset, they leave the cave and circle over the entrance. About one minute later they separate into small groups, each group using a flyway to a feeding area. The flyways are often no more than 16.4 ft (5 m) wide and the foraging area is usually within 820 ft (250 m) of the cave. They feed for about 30 minutes in the evening. Then they return to the cave where they remain until about 40 minutes before sunrise, when they again feed for about 18 minutes. There are some minor variations in activity patterns dependent on season, particularly related to cool temperatures and heavy rain, which discourage activity.

Feeding ecology and diet

Some have suggested that the hog-nosed bat is a foliage gleaner, taking insects directly from leaves and twigs, or even that it hunts near the ground. However, according to other observations, it is thought to catch insects on the wing as it flies around trees and bamboo. This view is supported by an analysis of its feeding buzzes, which are 3.5 ms-long and rather intense and not suited to a gleaning mode of feeding strategy. The stomach contents of one adult male included small beetles and other small insects.

Reproductive biology

In Thailand, a female with a single young was collected in May and an apparently pregnant female was caught in April. The time of birth would therefore appear to coincide with the onset of the summer rainy season. This species is thought to be polygamous.

Conservation status

Endangered, since it is considered to have a small distribution, a continuing decline in habitat quality and a continuing decline of a small, single population. The population in Thailand has been estimated at about 2,000 individuals. Its status has not been reassessed since the discovery of a second population in Myanmar.

Significance to humans

In Thailand, many visitors come to the Sai Yok National Park, which was declared a protected area in 1980 specifically to help conserve Kitti's hog-nosed bat. In the past this has led to some disturbance of the bat's roosting sites.

Resources

Books

Hutson, A. M., S. P. Mickleburgh, and P. A. Racey. Microchiropteran Bats: Global Status Survey and Conservation Action Plan. IUCN/SSC Chiroptera Specialist Group. Gland, Switzerland and Cambridge, UK: IUCN, 2001.

Periodicals

Bates, P. J. J., T. Nwe, K. M. Swe, and S. S. Hla Bu. "Further New Records of Bats from Myanmar (Burma), including Craseonycteris thonglongyai Hill 1974 (Chiroptera: Craseonycteridae)." Acta Chiropterologica 3, 1 (2001): 33–41.

Duangkhae, S. "Ecology and Behavior of Kitti's Hog-nosed Bat (Craseonycteris thonglongyai) in Western Thailand." Natural History Bulletin of the Siam Society 38 (1990): 135–161.

Hill, J. E. "A New Family, Genus and Species of Bat (Mammalia: Chiroptera) from Thailand." Bulletin of the British Museum (Natural History) Zoology 27 (1974): 303–336.

Hulva, P. and I. Horacek. "Craseonycteris thonglongyai (Chiroptera: Craseonycteridae) is a Rhinolophoid: Molecular Evidence from Cytochrome b." Acta Chiropterologica 4, 2 (2002): 107–120.

Surlykke, A., L. A. Miller, B. Mohl, B. B. Andersen, J. Christensen-Dalsgaard, and M. B. Jorgensen. "Echolocation in Two Very Small Bats from Thailand: Craseonycteris thonglongyai and Myotis siligorensis." Behavioral Ecology 33 (1993): 1–12.

Paul J. J. Bates, PhD