Bats fly out of a cave in Mulu National Park.
RECENTLY, one summer’s evening, whilst I was working late on my laptop, my dog shot upright from her bed and something fluttered across my vision. Thinking that my eyesight was failing or that I was ‘going batty’, I was 70 per cent sure that I saw a bat. I then searched for it in the house, there and then, and again the following morning, but to avail.
The next evening the same thing happened. I quickly turned off the light and heard a thump. With the aid of a torch, I saw a bat wriggling across my floor and, grabbing a tea towel, I gently picked it up and released it into the night. Probably a colony of bats is roosting by day in my attic but this member must have entered through my open bedroom window. Many years ago there were numerous bats in summer time flittering around my house at night, but less frequently today as more pesticides are sprayed on crops and thus fewer live insects are around for this species of bat to feed on.
Species
Over 1,300 species of bat are found worldwide apart from in the Polar-regions and they have been in existence for 52 million years.
They are classified into two main species. Firstly, Microchiroptera, which use echo-location in their movements and are mainly insectivores. However, a few of these species (30 per cent) do drink blood and eat small fish. The second major species are the Macrochiroptera, which rely on smell to locate nectar and fruit, and do not use echo-location. The zoological order of bats, Chiroptera, literally means ‘hand-wings’ in Greek.
Echo-location
Although bats possess eyes with reasonably good vision, the Microchiroptera species depend upon their ears when sending out and receiving pulses on ultrasonic frequencies as they fly at night. These frequencies are beyond the range of human hearing. This form of navigation is not unlike the sonar beams that naval destroyers use when detecting the location of submarines. Sophisticated electronic equipment, devised by zoologists, can now pick up these bat signals and identify individual species of bat by the frequency of their calls, volume and number of signals transmitted.
When setting out on its nightly flight, a bat usually emits 10 calls per second but when detecting an insect, the transmission rate increases to 20 calls per second. This ability to detect flying insects is called ‘hawking’.
Bodily structure
Local dialects, in the various regions of England, refer to a bat as ’batmouse’, ‘fluttermouse’ or ‘airey-mouse’ and not surprisingly because of its mouse-like body. Bats contain the essentials of mammalian structures and functions.
When I detached ‘my bat’ from the tea towel, it tried to wriggle out of my hand in an ungainly fashion. Its wing membranes had an unusual and curious feel and its fur felt like that of a tame mouse. However, its somewhat ugly face and ear shapes would not warrant entry into a beauty contest but I could feel its pulsating heart beneath its rib cage. There was a mysterious beauty in this warm-blooded animal.
Its wings had finger-like bones with a thin membrane of skin (the patagium) stretched beneath each finger. At the end of one thumb was a claw, often known as the ‘bat thumb’, which it uses effectively to climb and crawl and, moreover, to clean its ears. Roosting in daylight hours, all bat species sleep or hibernate in colder climes by hanging to rafters, branches of trees or rock faces with their claws. A locking mechanism in their tendons prevents them from falling off.
A Pipistrellus pipistrellus feeds on an insect.
British bats
‘Bats in the belfry’ is an old English expression with no real substance for bats would preferably choose warmer locations than a belfry to roost by day and hibernate in winter. Such chosen locations are house-attics, farmers’ barns, and limestone caves where there is a constant temperature of 10 degrees Celsius. In fact, there are 18 species of microbats found in the UK. Where I live, in South West England, there are two species that particularly interest me.
The Common Pipistrelle (Pipistrellus pipistrellus) or ‘my bat’ is the tiniest of European bats and roosts in houses but leaves its non-aromatic droppings in attics. It tends to fly back and forth with repeated jerks of its wings as it catches and ingests insects on its flight paths.
Each night it will devour the equivalent 50 per cent weight of insects to its own body weight.
The Greater Horseshoe bat (Rhinolophus ferrumequinum) is now only spotted in my neck of the woods. It is so named because of a distinctive horseshoe- shaped piece of skin that it has around its nostrils. These bats catch larger insects in flight and even eat dung beetles from cowpats.
Malaysian bats
Malaysia proudly hosts 125 bat species which, in fact, is 10 per cent of all the world’s bat species. The benefits of insectivorous bats are valuable to the rice farmer in ridding insect pests. To the durian and banana farmers, the frugivorous bats may eat some of the crops but are also natural pollinators and assist seed dispersal amongst rainforest plants.
My most memorable sights of Malaysian bats have been at dusk on the Kinabatangan River in Sabah and especially on the nightly exits from the Niah and Mulu cave systems in Sarawak. Interestingly, in both cave systems, the rooftop nesting of swiftlets and hanging bats by day do not intertwine.
As dusk approaches the day time insect hunting swiftlets return to their cave’s entrance on one side whilst the night time bat hunters depart on the other side of the entrance.
Their traffic lines are clearly cut. In Deer Cave, at Mulu, it is estimated that a colony of as many as a million plus ‘flying foxes’ dwells there.
Alfred Russel Wallace, in his exploration of ‘The Malay Archipelago’, mentions little of fruit eating bats, other than in cooking.
Robert Shelford (a former curator of Sarawak Museum) in his 1916 posthumous book, ‘A Naturalist in Borneo’, precisely describes the features of these bats. I have seen giant fruit bats, by day, hanging from tree branches in Mauritius, the Seychelles and in Madagascar but, in Borneo, there is a specialist fruit bat …
Dyak fruit bats
Dyacopterus spadiceus and Dyacopterus brooksi are two smaller species from the larger versions of the fruit bat species. With a body weight of less than 150 grams, and short grey fur with silvery streaks, it has two claws on each thumb. Living amongst the rainforest’s canopy, both species thrive on natural fruits and especially on fig varieties. Some have been recorded in peat and mangrove swamp forests.
Little is really known about the reproduction or habits of these species but it is thought that they lactate their babies from June to September whilst nesting in a tree-hollow.
Male bats of these species possess mammary glands – the only male mammal in existence to do so – suggesting that both female and male bats share in the feeding of their offspring. Speculation exists in the zoological world as for the reason for this.
Could the males have ingested certain leaves containing oestrogen-like compounds, thus stimulating milk production or are they stimulated by eating pesticide contaminated fruit which may imitate the effects of the hormone oestrogen?
As with all bat species, we know so little about their lives but, as I sign off, I shall watch these flittering or fluttering animals in my garden later tonight.