Bats 2

Bats - masterful mammals of the night

As the African sun sets each evening, moths, beetles, mosquitoes and other nocturnal insects take to the wing. Unseen by humans, many are attracted to white-blossomed flowers which release their sweet or pungent scent into the still air. Of course, the plants are advertising nectar to lure their pollinators. This relationship is the basis for a web of life, which includes the bats which either prey on the nocturnal insects, or feast on the fruits which develop after pollination.

Africa is home to over 150 bat species, belonging to two distinct groups. The fruit-bats or so-called 'flying foxes' belong to the sub-order Megachiroptera, while the insectivorous bats belong to the sub-order Microchiroptera. Although the bats from these two groups share the obvious feature of wings formed by skin-webbing, there are significant differences in their anatomy which suggest that they may, in fact, have distinct evolutionary backgrounds. The fruit-bats have large eyes, muscular tongues and fox-like snouts which show affinities to primitive primates (such as the lemurs of Madagascar), while the insectivorous bats have small eyes, complex noses, and emit high-frequency sounds which enable them to navigate in the dark by echo-location.

Bats are relatively easy to see at dusk when they emerge from their daytime roosts to hunt or forage, but most are rather difficult to identify. Unless the call of a particular species is known (and can be detected with sonar equipment), or an individual can be captured in a fine net, it is practically impossible to identify most species. There are several exceptions, however, and some bats allow closer scrutiny.

The large fruit-bats typically roost in trees (where they cling to lateral branches) or under open roofs, so may be readily observed and photographed. Many of these bats have white tufts ('epaulettes') of fur at the base of their ears which serve as signals to others of their kind and also demarcate scent glands. The Epauletted Fruit-Bats have a clear bell-like call ('ping') which is used to maintain contact with group members, and may be seen flying around fruiting trees (figs are particularly popular) with the aid of a torch. These large bats are known pollinators of the massive Baobab, and the distinctive Sausage Tree.

Most of the smaller insectivorous bats roost by day in caves, tree cavities or closed roofs. Some are adapted to spend their days in the rolled up leaves of banana plants. The Mauritian Tomb-Bat and Yellow-winged Bat take up more conspicuous day roosts, and the latter species is often encountered in Tanzanian savanna. Bats may also be found by chance, such as when a disorientated individual flies into a house.

One frequently asked question regarding bats, is: "why do they hang upside down?" Every mammal, bird and other organism has a structure adapted to a particular lifestyle, and there are at least two primary reasons for bats to roost in this way. Unlike birds, bats are unable to launch themselves into the air from a position on the ground. Their tiny hind legs do not allow them to run in order to build up the necessary takeoff speed, and their wings don't produce enough lift to take off from a stationary position. By clinging with their claws to a high spot, they can simply fall into flight.

Hanging upside down is also a good way to hide from danger. During the hours when most predators are active, bats congregate in places where few animals go and most cannot reach. This allows them to disappear from the world until night fall. There's also little competition for these roosting spots, as other flying animals don't have the ability to hang upside down. Some specialised predators have developed ways to capture bats, with the Bat Hawk (of Africa and Asia) being particularly adept at capturing and swallowing bats on the wing. Goshawks and falcons can also capture bats at dusk, while some larger hornbills are known to prey on roosting bats.

The well-known Vampire Bat occurs in only in South and Central America and although it may drink the blood of goats and other livestock, its danger to mankind has been greatly exaggerated in fables. No African bats pose any direct danger to man, and should not be persecuted as they perform vital ecological functions.

- Duncan Butchart -

Posted: Mammals by CC Africa, Date: 21 November 2006