 What was the croaking sound of different frog species? You must have heard them before right? But did you know it is only the male frog that croaks and not the female ones? Interesting right? But why? Why do only males croak? In this short video we will try to understand the whys and hows of different interesting characteristics of this hopping jumping friend of ours the frog. So first thing first why do only males croak? What comes to your mind when I just told you this? What do you think? Well in the animal kingdom in any species if you see a particular characteristic is exclusively found in one particular gender then most of the time that particular character is to attract the opposite gender and the same is true for the frogs here. They croak to attract the female frogs. So the croaking is nothing but a mating call or you can call it as an advertisement call because it's the male frog advertising themselves as potential partners hoping that the female frog will like their song and come their way. Now the croaking which is a soothing love song for the female frog can be a little irritating to our ears right? Because it is so loud that it can be heard from miles away and it can go on for hours. So like how are these tiny creatures able to produce such loud sound and for so long? Because think about it you and me can never think of doing that you know if we think of screaming loudly we can't do it for a very long time right? So how are these tiny creatures able to produce such loud sound and that too for so long? Well you and me we have vocal cords okay? We have something called vocal cords in our larynx okay? And the air rushes through these vocal cords and we are able to produce any sound okay? But when it comes to frogs nature has blessed them with an additional thing which is called the vocal sac. Vocal sac and it looks somewhat like this. So these frogs they fill their vocal sacs with air which is attached to their mouth okay? And the air inside acts like a resonance to amplify their sound and that is how it becomes so loud. Amazing right? And since only males croak this vocal sacs are only present in the male frogs. So this is the story behind the croaking of frog which is nothing but a mating call and they do it with their vocal cord and vocal sacs okay? Now think of when you have last heard this mating calls of frog. Let me take a guess. It must be a time after sunset when it is dark outside right? And you must have been present near some water body like a pond okay? So let me write you must have been near some water source and it was monsoon or spring time. Now how do I know it? Well this is the ideal time and situation of the year for the frogs to mate and you probably must have heard them during those time of the year right? Well now let's analyze these situations. Darkness, water source and this monsoon and spring season. Why do you think they croak during the night? Well the first answer would be that the frogs are nocturnal animals and they are anyway very active only during the night time. It's not necessarily only during the mating season okay? They are anyways very active during the day. And also if they croak during the day time they will attract the unnecessary attention of their predators right? That is why night is the perfect time for croaking. And talking of predators do you know that frogs can escape the sight of predators by camouflaging with its surroundings. Look at this frog and look at the color of the leaf it is sitting on. They are exactly the same right? This is to fool their predators or enemies and this ability to mimic the color of its surroundings to escape from predators is called mimicry. Now let's move on to why these frogs need to be essentially near a water source and it should be monsoon or spring season. What do you think? What comes to your mind? Well one answer could be that frogs are amphibians. Let me write amphibians and amphibians can leave both on land and in water. Well that can be an answer. But if we are talking about croaking, croaking is a sound made to mate right? And the ultimate goal is to find a female frog and make her lay eggs and have as many baby frogs as they can. That is the ultimate goal of croaking right? Now the eggs of frogs are not like the eggs of hens or ducks that we normally see. They don't have a shell. So these eggs has to be laid in and around shallow water to protect them from drying out. And this is the picture of the eggs of frog. This is how they look like in water. And monsoon and spring is the time when our ponds, lakes and wetlands have enough water in them. So it makes perfect sense for a male frog to invite a female frog to a water source during these favorable seasons. And on top of that, do you know frogs never drinks water? They absorb it through their skin. So water is an inseparable part for the survival of frogs. Now this brings us to our next question. What happens to these frogs when the water dries up or freezes during summer or peak winter? Where do these frogs go? Well, frogs, unlike us, are poichillothermic. What does that mean now? Poichillotherms are those animals that do not have the ability to generate heat by themselves. So their internal temperature depends on the environmental condition. They are also called cold-blooded because they need external factors like the sun or wind to keep their thermal balance. On the other hand, you and me, we are mammals, so we are homeotherms. We are capable of generating heat to maintain the internal body-thermal balance regardless of the environmental temperature. So during those days, frogs go into a phase of least physical and physiological activity. They slow down all their vital activities to save energy, like respiration and digestion, to maintain life and to go about that harsh environmental condition. And to survive that condition, they either dig burrows like these or they submerge themselves in the mud or they can find shelter under some dead decaying leaves. And they would stay there without much movement until the situation becomes favorable, until spring or next month soon. And this state of inactivation of the frogs during winter is called hibernation or winter sleep and during summer is called estivation or summer sleep. Now here I would recommend you to google about the Alaskan wood frog. It's a rare species of frog whose physiological activity do not slow down but stops completely when the environment is freezing outside. Their eyeball freezes, their body fluid freezes, they do not breathe, they don't have a pulse rate, their heart do not beat and in medical science they would be declared dead. But miraculously enough, as soon as spring hits Alaska, this frog hops back to life as if it was never frozen. And how this species manages to pull this off is still beyond the understanding of science. Amazing right? Nature never ceases to surprise us. So as we just saw in many parts of the world, these frogs get a very small duration in the whole year to be fully active, right? And they have to utilize this time very wisely. Apart from feeding themselves and getting ready for the next harsh season, they also need to copulate mate and produce new frog babies so that their species can continue to survive, right? Now to copulate the male frog croaks, the female frog reaches the male frog and the male frog hops onto the back of the female frog. Now to hop onto the back of the female frog and to hold her firmly is not an easy task to do. Because the frog's skin is slippery, it has mucus on top and it is not easy to hold on to such a slippery surface for long. But you know what, nature again has helped the male gender with something called the copulatory pad which is present on the first digit of their forelimb, with the help of which it gets a firm hold of the female frog. So till now, we have found two special characters which are exclusively male characters in frog. So one can easily distinguish between a male and a female frog with the help of these characteristics and this distinction in features between female and male frog is called sexual diamorphism. Now do you know which is the most common variety of frog in the Indian subcontinent? This is how it looks. It is called the Indian bullfrog and its scientific name is Rana Taigreena. Now this scientific name has currently changed to Hoplobatricus Taigreenas but you will find the old name which is Rana Taigreena in most textbooks. So this is the Indian bullfrog and this is how it croaks. Now let's talk a little bit about the morphology. As you can see they are stout and roughly triangular in shape. The dorsal skin is typically olive or green in color with dark patches while the ventral region down here is whitish or pale yellow in color. And the body is distinguished into a head and a trunk region. You don't see a neck in between or a tail. And the head has two small openings at the end of the snout. These are called the external nears or simply nostrils. It is just like the nostrils we have. And as you can see these frogs they rest in the squatting position. And they keep their hind limb folded like the letter Z. This is how they fold their hind limb and on disturbance they suddenly jumps by extending their hind limb to escape their enemies. The hind limb acts like a spring that throws the body into the air. So the major responsibility of locomotion is on the hind limb. That's the reason they are larger and more muscular than the forelimb. Now the forelimb has four digits in them while the hind limb it has five digits. And the digits on the feet are webbed when it comes to the hind limb. Which is useful when they swim. In the water the toes are spread apart and the broad webs they push against the water moving the body forward. That is how they swim. And apart from that what you can see clearly are these two large eyes on each side of the head. Now these big round protruded eyes have eyelids just like you and me. But along with that they have another membrane which is called the nictating membrane which can be opened and closed just the way we do with our eyelids. This nictating membrane helps to save the eyes from water and mud while these frogs are swimming and it also helps to keep these eyes moist when these frogs are on land. And it is not just the frogs that have these nictating membranes we see them in birds and reptiles as well. And behind the eyes and just below you can see a circular membrane. This is nothing but the ear drum and it is present on both sides. And this is called the timpana and they don't have the external pinna the external ear that we have they they directly have the timpanum on the outside. And this timpanum is tuned to the croaking of the male frog of the same species. That is how they recognize the male frog, copulate and form many more frog babies. So this was a short video about the external features and the life of this hopping jumping friend the frog. If you enjoyed learning about them you will definitely enjoy learning about their reproductive and their awesome digestive system which we will talk about in our future video.