The modifications between mammals may be,
a. BEHAVIOURAL such as hunting by groups instead of Hunting individually;
b. PHYSIOLOGICAL such as the ability to conserve Water;
c. STRUCTURAL such as to allow them to live in water or fly.
We said that all mammals have some qualities in common, they are:
1. They suckle their young ones with milk.
2. They all breathe and have lungs to respire.
3. All of them are more or less covered with hair.
4. All of them are WARM BLOODED animals; that is to say that their blood is warm and stays in their body at constant temperature.
Look at the picture given.
The three animals are entirely different in their appearance;
a bat , a seal and a cow. But they all belong to the same class of Animal Kingdom, the MAMMALS.
The reason they are grouped together is that, they have the four common characteristics as described above.
In fact mammals are far more diverse (looking different) than what the picture shows.
There are mammals living on land, in trees, underground, in fresh water, and in the sea.
There are mammals that can run, jump, swim, fly and even read and write!
Do you know that we human beings our self are mammals.
Some mammals are carnivorous (flesh-eaters) and some are herbivorous (vegetable-eating) like grandpa and some others like us are omnivorous (eat both flesh and vegetables)
Even though many other animals do have lungs; and the blood of birds are warm, they are not called mammals.
THE HAIR ON THEM AND THE MILK, ON WHICH THEY SUCKLE THEIR YOUNG ONES,
DISTINGUISH THE MAMMALS, FROM ALL OTHER ANIMALS.
Let us see the modifications described above one by one.
a. BEHAVIOURAL such as hunting by groups instead of hunting individually.
Some animals like Tigers, Leopard, and Bear etc. hunt individually. They go alone and hunt for their food. After getting their food, they eat alone. In the case of Lion, the lioness (female lion) will collect group lionesses and hunt together.
But some animals like lion, whistling wild dogs hunt as a team. You may take the example of ants, bees also. Ants and bees bring food and store at their home for every one including the new born to use.
Cattle, deer, sheep, giraffe, zebra all go as groups to graze in grass lands. You may call them as living in groups or sociable animals or GREGARIOUS animals. Human beings also are GREGARIOUS!
REMEMBER! ALL THE ANIMALS DESCRIBED ABOVE ARE MAMMALS
b. PHYSIOLOGICAL such as the ability to conserve water.
For example Camels have hump to conserve water , Polar Bears have thick fur to protect them from cold.
c. STRUCTURAL such as to allow them to live in water or fly.
The Blue Whales, the Seals (Sea lions), the PLATYPUS and the HIPPOPOTAMUS all have their body structure modified to live in water. The whale, seal and platypus have streamlined body to swim while the Hippos have soft skin with less hair to live in water.
Hippopotamus is a strange mammal. It lives during the day in the river waters and feeds on grass on land during night.
Like wise the Platypus is another strange animal too. It also lives in a tunnel made on the river banks and feeds on aquatic insects. For the most part of its life it lives in water.
Some mammals do fly, like BATS. It is interesting to note that no bat flies during the day. But very few birds like owl fly during the night. Even though they eat the same type of food; they do not fight among them selves for food.
’ Many wars among human beings have been waged for better lands, where food could be grown’.
It is difficult to see on earth, animals that do not fight for food.
Fact remains that Bats are flying mammals. We shall see in detail about bats shortly.
The hippopotamus is popularly known as the “RIVER HORSE”; because it lives mostly in African rivers. But it is not correct to call it a horse. It never resembles a horse. Perhaps if it could have been called as “RIVER PIG”, it may be correct; for it resembles more like a pig. Pigs have four toes just like the hippos. But the hippo’s toes have large nails and are webbed for swimming. Both have similar structure of teeth.
The hippos are powerful swimmers and can easily swim even against the current of water. Sometimes it walks at
the bottom of rivers. Even though it looks very fat, it does not have much of fat. Its body is mostly made up of meat.
During the day the hippos often look to be sleepy. This is because, hippos are nocturnal (active by the night) animals. Their staple food is grass. But they are known to eat corn or even sugar cane. In the wild it causes damage to these crops. In the night it goes for grazing and returns at dawn with stomach full of grass. It spends the day digesting the grass.
Do you know that the baby hippos (calf) are born under water? These calves ride on the back of their mother while in water for almost one year.
Well! Don’t you think the hippos are strange mammals?
Australia is a strange continent by itself as it has been isolated as an island for a very long time. The land of Kangaroos has lots of strange stories. Some of them are really true. So is the story of the EGG LAYING MAMMAL.
In the late 18th century, travellers from Australia brought an animal fur (hairy skin of animals) to the market. It reached the hands of a few NATURALISTS in Europe. The fur of this creature was like that of a mammal with a lot of hair; but instead of a mouth it had beak, looking like a Duck’s bill. Some of the scientists refused to believe that such an animal could exist. They said that whoever has brought the fur has made up the animal by joining the parts of a mammal and a bird.
Later a few scientists who travelled from Australia brought the whole animal preserved in Alcohol and made the Naturalist in Europe believe the existence of the strange animal.
This strange animal is called PLATYPUS .The animal looked half way between that of a mammal and that of a reptile. Perhaps it is by chance its beak looked like that of a duck. Investigations on the animal showed that it laid eggs like a bird or a reptile; but suckled its young ones like a mammal. We can call this extraordinary mammal as PRIMITIVE MAMMAL.
The home of the platypus is the long tunnel it digs on the banks of a river, a pond, or a lake. The tunnel opens under water. It stays in the long tunnel all day and comes out during the evening. It feeds on aquatic animals including small fish.
BATS, THE ONLY MAMMAL
CAPABLE OF TRUE FLIGHT
BATS are perhaps one of the most successful mammals on earth just like us. It has mastered the art of flying. They are the experts who have adapted themselves very well in nature. Their adaptation has helped them in such a way there is hardly any competitor for food, when bats feed. Bats belong to the order known to biologists as CHIROPTERA
Our bat is a great hero who patrols the night, seeking out the villains that torment and harass us. He uses his highly developed bat senses to zero in on the perpetrator, then with uncanny accuracy, he swoops down to nab the villain the mosquitoes and other harmful insects. He eats the same food as birds, but prefers to hunt at night.
Batman is the latest craze of children, perhaps outshining those adolescent ninja turtle and giving competition to the mighty Spiderman.
Our hero swoops down upon the villainous creatures and feasts on it, making life safer and more pleasant for us.
Batman is admired by all people, (the honest ones, of course), of Gothem. Our hero is feared and hated by the evils.
It is a pity that the real bat creatures of the world are also heroes as they help us in many ways, but are usually treated as if they were the villains.
The bat has been associated with all sorts of superstitions and tales for centuries. Perhaps it is because Bat is a creature of the night that he is so greatly misunderstood.
A common man thinks that
1. A bat is a flying rat who spreads.
2. Scares people in the night by tangling it self on human hair.
3. Scares you by entering you house and flying mad..
. In fact, the bat’s goals in life is to cruise the night skies seeking insects that plague us humans, quite often moths and mosquitoes, for his dinner. A single bat can eat hundreds of insects in a single night.
The bat gets into houses by accident and would like nothing better at that point than to get back out. As for human hair, bat has no attraction to that.
The bat holds the distinction of being the only mammal that can sustain flight. Most bats are better flyers than birds, being able to fly more slowly and with far better maneuverability.
The old saying “blind as a bat” is quite incorrect. No bat is blind, but has well developed sight and smell. Since sight is of no help in darkness, bats navigate by echolocation. Echolocation is much like radar; the bat bounces sound off objects to ascertain their direction.
Bats roost during the day in caves, hollow trees, under rocks or in old barns. Some live alone, others in groups. They usually produce only one young per year. This may be because bats have such a long life-span. Some live to about twenty years; the record is thirty one years.
The accusation that bats transmit disease, particularly rabies, is unfounded and has not bees proved as yet.
It is the humans that have made bats the victims. Often developers building houses will find a colony of bats, and wipe out the entire group. Insects often carry traces of insecticides that we spray on crops and gardens. When the bat eats the insects, the pesticides collected in the bat’s body cannot rid itself of the chemicals. Bats can die if the levels reach too high.
The insectivorous bats of our area cause no harm, but decreases the insect population.
If you still hesitate to appreciate the little bats that eat insects and occasionally make a wrong turn and explore our houses, consider the larger megabat of Africa and India.
If this bat came into your house, it would probably empty the house of human occupants not because it would cause any harm, but because its wing span is five feet!!!
ANCESTOR OF BATS
Birds and Bats have a great similarity between them. Perhaps this has made our scientists to say that both have the same common ancestor (fore fathers), the amphibious (animals that can live both on land and in water- like frogs) reptile.
Similarities between Bats and Birds
|1.||All are capable of flight||Most birds can fly|
|2.||Some bats eat fruit and nectar as food.||Some birds eat fruit and nectar as food.|
|3.||Some bats eat fruit and nectar as food.||Some birds eat fruit and nectar as food.|
|4.||Have two legs for hanging from a roost.||Have two legs for perching and walking.|
|5.||Warm blooded||Warm blooded|
|6.||Helps in cross pollination of flowers||Helps in cross pollination of flowers|
|7.||Found in all parts of the world , except polar regions||Found in all parts of the world, including polar regions.|
DIFFERENCES BETWEEN BATS AND BIRDS
|1.||All bats are nocturnal. (becomes active by night)||Most birds are diurnal. ( active by day)|
|2.||Has well formed mouth. Teeth are present in some species.||Has beak instead of mouth. No teeth.|
|3.||Has membranous( like soft cloth) wings||Has wings containing feathers|
|4.||Has hairs||Has feathers|
|5.||Gives birth to live young ones. Suckles the baby bats.(Mammal)||Lays eggs . (Oviparous)|
|6.||Does not build nest.||Builds nests during breeding season.|
|7.||Makes very feeble squeaking noise||Bird calls can be very loud.|
|8.||Has distinct ears||Does not have ears|
|9.||All bats , more or less , have the same colour or body pigment.( Greyish black to dull brown). Male and female have the same colour.||Birds are multi coloured. Males are brighter coloured than females.|
|10.||Locates prey and places through echolocation. ( by the reflection of sound waves as echo)||Locates prey and places by sight.|
|11.||Has tail||Some of the feathers function as tail feathers.|
NATURAL ADAPTATION IN BATS
We saw that there are mainly three important modifications in Mammals. These modifications between mammals may be,
a. BEHAVIOURAL such as hunting by groups instead of
Most bats roost (take rest or sleep) during the day as groups. This helps them to defend themselves as a group.
b. PHYSIOLOGICAL such as the ability to conserve
The membranous wings help in radiating heat and helps in cooling the body system of bats during flight. ; when the bats land on tree or their nesting site, after flight, the elastic membranes in its wings collapse like an umbrella folded, so that heat loss could be reduced.
c. STRUCTURAL such as to allow them to live in water
The fore limbs of bats have become elongated during evolution, especially the four fingers, the index finger to the little finger, which supports Bats’ membranous wings. The thumb is free and the bats use it for hanging upside down, or climb about in trees or crawl on their nesting site.
Thus we see an example for all the three modifications of mammals in BATS. Therefore, I wanted to write about this remarkable mammal.
BATS BIRDS and their WINGS
Birds and bats are both the only winged bipeds (two legged), naturally adapted to be active by day (birds are diurnal animals) or active by night (bats are nocturnal animals).
Why do bats fly after Sunsets?
When we run or jump or when we do exercises or even when we cycle, our body becomes warm and we feel hot. At that time our body sends out water in drops to cool our body system. We call this process as perspiration or sweating. We as mammals have sweat glands. Sweat glands are like tear glands that make us cry when we are sad. Sweat glands send water out when our body becomes warm. During this time sometimes our heart beat increases and we find it difficult to even breathe. This we call as panting for breath.
Similarly birds and bats fly a lot. During their flight they flap their wings; there by they do a lot of exercise. As they need lot of energy to fly they eat lot of food. Their rate of metabolism is faster than the mammals. During digestion these food are also burnt to give heat.
The extra heat generated by animals under normal conditions would result in overheating, fever and death.
Birds have lungs, but they do not have sweat glands. So they cannot sweat like us. But birds have air sacs. Using lungs and air sacs birds remove their body heat as fast as the heat is produced. One of the major functions of air sacs, a feature peculiar to birds, is to promote internal perspiration. ‘Water vapour diffuses from the blood into these cavities and passes out via lungs with which they are indirectly connected’. Thus birds are able to cool themselves. THEREFORE BIRDS CAN FLY DURING THE DAY, WHEN ITS IS HOT. OUR SUN NOT ONLY GIVES US LIGHT, BUT IT ALSO WARMS OUR PLANET.
Bats do not have air sacs like that of birds. Hence they do have some difficulty in removing the excess heat from its body.
We already saw that the fore limbs of bats have become elongated during evolution, especially the four fingers, the index finger, middle finger, the ring finger and the little finger.
These four fingers support the membranous wings of bats. But each of the fingers can move independently, so that the bat could make stable alteration to the wing surface. This helps bat in its flight manoeuvres. The membranes stretch from the fingers backwards, supported by the sides of the body, the back, the legs and the tail if present. We can perhaps say that the bats have developed a parachute like expansion of the skin of the sides of the body and limbs.
The thumb is free and the bats use it for hanging upside down, or climb about in trees or crawl on their nesting site.
Two reasons may be cited for their activity by night:
First bats cool themselves by radiating heat through their naked wings. This method of cooling will be disadvantageous in sunlight, when heat would be absorbed rather than lost in radiation. Black or Grey colours take heat in while White colours reflect heat back. Since all the bats are coloured grey to deep brown, their body will take in (absorb) heat from the sun. This will increase the body temperature of bats. Hence they fly during the cooler times such as evenings and night. (Note: Black colour or shades take in heat while white colour or light shades reflect heat; hence we use black umbrellas during cooler rainy days and white umbrellas during hot summer)
How do Bats avoid obstacles during its night flight and how does find its food?
Secondly bats posses a well-developed sensory system for flight navigation at night.
The insect eating bats have poorly developed eyes but an excellent echolocation system. These bats can navigate easily even in pitch dark to find their food. They will not mind moving even if they are blind folded. They emit a constant train of sound pulses during flight or even when active on the ground. The actual sound frequencies range, from about 15KHZ (Just audible) to 150KHZ, with wavelengths ranging from 2.2 – 0.22cms. Of these ranges leaving the rare extremes the normal range, has been observed to be 20-100 KHZ. The sound pulses also vary from 0.25 milliseconds to 60 milliseconds. It has been observed that the insectivorous bats are capable of avoiding even wires, which are barely 0.1mm thick! These bats are capable of locating and catching their preys even in mid air.
On the other hand the fruit eating bats or FLYING FOXES are less specialised for echolocation and would be totally helpless if blind folded.
Article by Mr. R Venkata Ramanan. Chennai based educational consultant. See linkedIn profile.
R Venkata Ramanan
Padmini V Ramanan Educational Resource Centre
4/27-B, IIT colony 1st Street,
9444127974 ; 91-044-22463148