by Kiyoshi Takahashi
Bats are probably the most misunderstood and discriminated against mammals (you all know they are not birds) in the natural world. Despite the typical image imprinted to many people's minds, there are only three known blood-sucking species of bats out of 900 known species in the world. They must fear for humans, not the other way around, as some people still catch and eat them.
My earliest encounters with bats were in my boyhood some 60 years ago. Bats were plentiful then in the countryside of Japan where I used to live, and though not plentiful anymore, they still live there in large numbers.
At dusk, several of my buddies and I used to wait at the grass fields in the village where I lived with my family in a small town in the Japanese country side. As soon as black things starting to fly, we removed our worn-out straw slippers that were our regular footwear and threw them into the evening sky. My slippers were always conveniently worn with many threads of straw hanging out! I never owned a new one, because my four older brothers gave me their used ones, to justify asking mother to get them new ones. Never mind, I fully utilized the worn slippers to my advantage in my assignment!
Just come out of roosting sites, plentiful in those days, with empty stomachs, the bats grabbed the "flying objects.” We just hoped their "feet" would tangle up with the threads of worn straw slippers. Once in a while, a poor bat would tangle up with a child's slipper, which was too heavy for the bat to carry away, and tumble down to the ground. When the moment arrived, we formed a circle around the poor bat and shouted and screamed with joy and fear! What a stressful moment it must have been for the bat. The bat might have thought we were going to suck its blood! However, not one of these pre-scholars had the courage to touch it or closely inspect it. Luckily for the bats, they soon untangled the damn straw slipper and flew away. We went home happily to tell the exciting story to Mother. Hey, bats, please forgive me as I did not know anything about natural science in my boyhood, but I assure you that we never killed your predecessors. It was simply a fun way for rural boys living in the days before video games to waste time. In those days, through rather rowdy acts, I learned a lot about nature and life by feeling, touching and being a part of the natural world.
In fact, bats are one of the most unique and important mammals to us humans. Bat biology, their behavior and natural history are not understood very well yet, even though they are known to have evolved shortly after the extinction of the dinosaur. The bat is believed to be evolved from insectivores like voles and shrews 40 to 50 million years ago, not the rodent family like squirrels or mice. They are the only mammals that can fly, unlike some other common "sky-going mammals" such as the flying squirrel which only glides. When bats come out of their roosting site, the life support of most species are "up in the air" to survive. Only few feed on the ground. The wing is an extension of skin stretched around the bone structure of the arms, fingers and legs. A very long arm supports the front edge of the large wing, and long first, second and third fingers perform the quick maneuvers needed to catch flying insects. Although the wings are not designed for fast flying, some bats can fly up to 50 KMH for up to one hundred fifty kilometers to feed. However, most of our local bats feed on local insects on and around a water body. Their thumb protrudes from the leading edge in the middle of the large wing or at the end of the arm, and it can grab or hook on objects. The Latin name for bats is Chiroptera, meaning "hand wing.”
Bats have developed the ability to self-adjust their body temperature by using an internal thermostat. When the air temperature becomes lower, usually lower than 12 degrees Celsius, the normal body temperature of about 40 degrees Celsius is lowered to as low as 5 degrees to go into torpor, or dormancy, to conserve energy. When torpor goes for a longer period of time, it is called hibernation. This slow-paced lifestyle is one of the reasons for the longevity of bats, up to 30 years for such a small animal.
There are at least 5 to 6 species of bats in our TriCity area, and maybe some 12 species in Northwest. We are close to the northern limit of their territory. Bats of our neighborhood in the Lower Mainland British Columbia either hibernate or migrate to warmer regions in the winter time, but most likely they hibernate as they are not a long distance flyer. Who wants to fool around in the winter when there is not enough food and it rains all the time?
Bats not only catch insects by mouth, but some also scoop flying insects on their wing or the tail membrane that stretches between their rear legs, then eat the trapped insects on the fly. Their beady eyes seem to be not very reliable, but they can fly in complete darkness. How? As night-going animals, bats developed echolocation, or sonar detector. They locate prey in the dark sky using their radar. An ultrasonic pulse emits from deep in their mouth, hits a flying object and reflects back to their disproportionably large ears. If the object does not move, they recognize it as a structure. If it is a moving object, they calculates size, speed and flying direction to capture it. Bats do not like rain because they cannot use echolocation effectively to hunt for foods as the raindrops interfere with the echo.
Each species have their own sound frequencies, which enables us to identify the species without actually seeing them by analyzing ultra sounds. Modern electronic devises can analyze the sound wave to read what they are doing, or convert audible sounds to human ears and analyze the frequencies. Many bats also produce audible sounds to communicate within the family or during their non-hunting flights.
The ultrasound detector is by far the best method to study bats without disturbing them. The night scope is another method to study bats but it does not give full detail for their flight movement. The Mist Nest, which the Japanese developed a long time ago to catch flying birds, is suitable to catch them safely but it gives bats a tremendous stress.
Unlike most bats in Canada and the northern USA, bats in the American south like in Texas or in Southeast Asia behave differently. Both insectivore and fruit bats are active throughout the year. Nursing mothers of insectivorous bats eat about their equivalent in body weight of insects per night; average adult bats eat somewhat less. The 20 million bats that emerge from the Bracken Cave in Texas together are estimated to eat an average of 200 tons of insects per day. That is EVERY NIGHT!
Many bats in tropical regions are so-called Fruit Bats, non-carnivorous. They feed on fruits, berries, nectar and pollen in the tropical forests and for millions of years they have played the very important role of maintaining thick forests by pollination. Some bats catch fish or amphibians and only four species feed on animal blood. However, the amount of blood they steal is so small that most animals do not notice they donated a small part of that important material for life.
Bats are important allies to human to control insects and maintain forests. Unfortunately, we do not normally see them easily at night and they are loosing their habitat seriously due to human invasion in the name of development.
This article was originally published in the Burke Mountain Naturalist's newsletter in 2002.
