ORIGINS
Bat fossils date back to around 50 million years ago and are, interestingly, almost identical to those found today.
Before humans began to affect their numbers, bats were once much more common and must have dominated the night skies in some places.
They are classified as mammals as they have hair, give birth to live young which feed on milk produced in mammary glands.
Bats are the only true flying mammals and are so unique that they have been placed in an order of their own: Chiroptera (meaning ‘hand-wing).
Diversity and Distribution
The approximately 1200 species of bats make up a quarter of all mammal species, and are found throughout the world except for the most extreme desert and polar regions.
However the majority of species occupy tropical forests.
About 80 species occur in southern Africa, of which approximately 65 occur in South Africa and roughly a dozen have been recorded in Gauteng.
Bats come in an amazing variety of sizes and appearances, weighing from a mere 2 grams up to 1.1 kilograms. There are many different fur colours and one species is even furless.
Others have enormous ears, nose-leaves and intricate facial features that may seem bizarre but allow them to perform very sophisticated navigation by sound.
NAVIGATION, HIBERNATION AND MIGRATION
All insectivorous bats (and one group of cave dwelling fruit-bats) navigate using high-frequency sounds, enabling them, in total darkness, to detect obstacles as small as a human hair.
Sounds are emitted in the ultrasonic range from 20 to 210 kilohertz (frequencies of up to about 20 kilohertz are audible to humans) from either the mouth or the nose.
In addition, bats are not blind and many have excellent vision.
In temperate regions, cold winters force bats to migrate or hibernate. Most travel less than 500 km to find a suitable cave or abandoned mine, where they remain for months, surviving solely on stored fat reserves. However, several species are long-distance migrators, travelling from as far north as Canada to the Gulf States or Mexico for the winter.
The giant-sized Straw-coloured Fruit Bat makes long migrations between East and West Africa flying at altitudes of up to 200 m and at speeds of up to 30 km/h.
Hibernation enables bats to ‘switch-off’ their body’s energy-expensive heating mechanism, thus allowing them to survive cold winters when insects are not available. Body temperatures may even approach freezing point during this time. Prior to hibernation, bats build up their fat reserves, which may have to last up to six months.
Disturbing hibernating bats can have tragic consequence because they have limited fat reserves and undue arousal costs large amounts of energy and may result in the bat waking up before winter is finished and consequently, starving.
Typically, bats are very loyal to their birthplaces and hibernating sites. Exactly how bats navigate large distances is still a mystery. They may use mountain ranges and other visual landmarks, as well as information passed from one generation to the next.
Reproduction and Longevity
Female bats of many species have the ability to store unfertilized sperm from the male in their uterus throughout the entire hibernation period (i.e. mating occurs before hibernation).
Other species are able to delay implantation of the fertilized egg throughout winter or to retard the development of the attached embryo over winter.
Pregnant females often form maternity colonies, segregated from males and non-reproductive females. Births typically occur several weeks later.
The young suckle from their mothers and grow rapidly, often learning to fly within a few weeks.
Some tropical bats engage in elaborate courtship rituals. Male epauletted bats sing and flash large fluffs of white shoulder fur to attract mates.
For their size, bats reproduce very slowly. On average, mother bats rear only one pup a year, and some do not give birth until they are two or more years old.
Bats are exceptionally long-lived, often attaining 15 to 20 years; certain species survive for more than 30 years.
FEEDING AND ROOSTING BEHAVIOUR
About 70% of bats eat mainly insects and catch most of their food in flight. Wing shape varies according to the bat’s lifestyle.
Those that forage in open areas tend to fly fast and have long, narrow, tapered wings like swallows. Bats that feed in heavily vegetated areas are designed more like butterflies. They have short, broad wings that allow them to fly at slow speeds and make tight turns. While some bats catch insects with their mouths, others first scoop up the insect in their tail or wing membrane.
Many tropical species feed on fruit or nectar, sometimes exclusively. Nectar-feeding bats have long tongues and noses which fit glove-like into the flowers on whose nectar they feed, and which they also pollinate.
A few bats are carnivorous, hunting small animals such as fish, frogs, mice, birds and sometimes even other bats. Species of blood-feeding vampire bats are found only in Latin America (not throughout the world as many people assume).
Water is drunk on the wing by skimming over the surface of bodies such as ponds and streams, and gulping a mouthful or using their tongue as a ‘straw’.
This is similar to the way many birds drink water.
Bats can be found in most kinds of shelter, although they are best known for living in caves, often in huge colonies numbering millions.
In South Africa probably the biggest colony is at The De Hoop Cave near Bredasdorp and contains about 300,000 bats.
Building roofs with their stable climates and abundance of secure crevices within, are often readily exploited by bats which in the wild would roost in holes in trees, or under loose bark or in gaps between rocks. In the Gauteng region, a number of different bat species are regularly found roosting in roofs such as the Egyptian Free-tailed Bat, the Cape Roof Bat and the African yellow bat. Several species such as the Egyptian slit-faced bat will often roost in abandoned buildings in rural areas.
Tropical bats occupy a wider range of roost sites than temperate bats. For example, so-called Banana Bats prefer the curled young leaves of bananas and wild Strelitzia plants. ‘Tent-making’ bats from South America make tent-like roosts by biting through the midribs of large leaves. Others live in animal burrows, termite and bird nests and flowers.