Twenty-four percent of all placental mammal species are bats. There are two Suborders; Megachiroptera (which has only one family; Pteropodidae) and Microchiroptera (comprising 17 families). They are the only mammals that posses the power of true flight, unlike the gliding flying lemur.
The skin on the back and legs of a bat spread out and join to form the patagium, or wing membrane. Wingspans vary enormously from the largest bat; Rodriquez flying fox (Pteropus rodricensis) with a wingspan of 1.5 m, down to the smallest species; hog nosed bat (XXX) who's wingspan is a minute 15 cm. The wings are stretched out from the body to the four elongated fingers. Only the thumb stands proud of the patagium and is used to grasp objects or perches. The wings themselves are made from two layers of skin with blood vessels and nerves running between them. To enable flight, the wings are supported by fused vertebrae, flattened ribs and a strong collarbone. To allow the downbeat of the wings to provide enough lift, large muscles are attached to a ridge that runs down the centre of the sternum. Unlike all other mammals, bats legs have been rotated around so the knee and ankle bend 'backwards'. This allows bats to hang upside down and manoeuvre themselves around with little use of their arms. Bats can walk around on the ground on all fours, but find it very difficult to get airborne. They actually take off from effectively falling out of a tree, spreading their wings and then flapping to gain height. When bats sleep, they fold their wings around their body to keep warm. They also roost in large numbers in old houses, trees, or caves. It is uncertain why they do this, but warmth is thought to be a factor.
Although a bats' eyesight is well developed, hearing and sense of smell are more important in the capturing of prey. Megachiropterans have large eyes see prey, whereas Microchiropterans have specialised ears and nose to allow echolocation. A microchiropteran will make clicking sounds in the larynx which are directed by the enlarged nasal structure called the nose leaf. If the sound hits a flying insect for example, it is then bounced back to the bat. Their especially large ears are ultra sensitive and pick up the noise, enabling the bat to locate the source of reflection. The time delay between the bat releasing the sound and hearing it come back again reveals the size and location of the object or prey. The closer the prey is, the shorter the time delay.
Egyptian fruit bat
Length: 14-16 cm
Weight: 80-100 g
Social unit: Group
Region: West Asia, North Africa (Egypt), West, East and South Africa
Brown long-eared bat
Length: 4-5 cm
Weight: 7-14 g
Social unit: Group
Region: Europe and Central Asia
Status: Lower risk
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Author: Emma-Louise Nicholls
Last updated: 20th November 2005
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