Lesser sheath-tailed bat (Emballonura monticola)
|Synonyms:||Emballonura peninsularis, Emballonura pusilla|
|Size||Head-and-body length: 40 – 47 mm (2)|
Tail length: 11 – 14 mm (2)
Forearm length: 43 – 47 mm (2)
|Weight||5 – 7 g (2)|
Classified as Least Concern (LC) on the IUCN Red List (1).
The angular features of this small and timid bat make it easy to recognise. It has a pointy, simple nose with no noseleaf, large black eyes, and triangular ears. The fur is extremely smooth and shiny, varying in colour from reddish brown to dark brown, and fading to buff brown on the underside. In common with other members of the Emballonuridae, or sheath-tailed bats, the lesser sheath-tailed bat has a short tail that protrudes from the interfemoral membrane between the legs, unless the legs are stretched, when the tail retracts into its sheath (3). The wings are black, and so long that when at rest, they have one more fold than those in other bat families (4). Their shape means that the bat can fly fast and straight in forest gaps, such as over streams (3).
The lesser sheath-tailed bat is found in southern Burma, Thailand, Peninsular Malaysia, Sumatra, Java, Borneo, southern Sulawesi, and many offshore islands (5).
With a body and wings adapted to foraging in forest gaps, the lesser sheath-tailed bat is found above streams and around tree falls where it can take advantage of its high speed, but poor in-flight agility. It is found in primary rainforest up to 1800 m, where it roosts in groups in large tree holes, rock crevices and at cave entrances. Each bat positions itself flat against the wall of its roost, using a forearm to prop itself up (2) (3), and will remain alert when roosting (4).
The echolocation calls of this delicate bat are extremely distinctive, starting with a short sweep up the frequency range, followed by a steady constant frequency component between 48 and 51 kHz, and finishing with a final sweep down through the frequency range. Each call lasts just 6 – 8 milliseconds (6). The lesser sheath-tailed bat uses these calls to orientate itself in the forest, and to detect small insects to feed upon, by waiting for the returning echo of the call and building up a detailed picture of its environment.
It is thought that the lesser sheath-tailed bat has two breeding seasons each year; one in February and March, and the second in October and November. However, individuals have also been found to be pregnant at other times of year (2). Each female gives birth to a single pup, which she prevents from falling to the floor of the roost by scooping it to her body with her wing. At birth, the pup weighs a quarter of its mother’s weight (this is normal in bats, but extraordinary in much of the rest of the mammalian class). The mother will forage with her pup clinging to her belly until it becomes too heavy to carry. Soon afterwards the pup is weaned, and within a year it will become a mature adult (7).
The rapid increase in land devoted to growing oil palm has resulted in extensive loss of primary forest. Together, Malaysia and Indonesia export 88% of the world’s palm oil, for use in products such as margarine, lipstick and detergent. Deforestation continues at a steady rate for conversion to agricultural land and building communities, and despite the contribution of many bats in the control of insect crop pests, persecution of bats is also a threat (8).
Deforestation of primary forest for oil palm plantations, including within protected areas, is an issue of major concern and one that relies on both governmental action and consumer concern. Some large retailers have agreed, in collaboration with the WWF, to source products containing palm oil from plantations that are not on deforested land (8). Many scientific and charitable groups contribute to bat monitoring and local education programmes that can help to reduce persecution and raise awareness of the natural assets of the land (7).
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- Echolocation: Detecting objects by reflected sound. Used for orientation and detecting and locating prey by bats and cetacea (whales and dolphins).
- Primary forest: Forest that has remained undisturbed for a long time and has reached a mature condition.
IUCN Red List (December, 2009)