Home  

Life in Cold Blood Blooded Truth

where reptiles and amphibians are sometimes thought of as primitive dull and dim-witted Reptiles have scaly skins and amphibians soft moist ones. None of them live at a uniform pace but switch from the fast to the slow lane within a year or an hour. Unlike us they get their energy directly from the sun and although being called cold-blooded might suggest they are unemotional they can be touchingly warm-hearted as mates and as parents. And that's just the beginning. There are a whole lot of other warm-hearted truths to be discovered that give the phrase life in cold blood a completely new meaning. The Galapagos Islands. Some of the reptiles that live here are particularly skilful at solving the problems of getting their energy directly from sunshine. Marine iguanas face a major thermal challenge every morning of their lives. During the night their bodies cooled and now they must warm up quickly in order that they can become active and start feeding. Their bodies and skins are black which is very efficient at absorbing heat and they bask with their black flanks broadside to the sun. The rate at which they absorb warmth is invisible to the naked eye but very clear indeed to a thermal camera. First thing they're cold and purplish blue. But slowly as they warm up a golden glow spreads through their bodies and eventually after half an hour or so they become as hot as the rocks beneath them. Once they are thoroughly warmed up marine iguanas can maintain their body temperature just about as constantly as I can and what's more at about the same level or indeed slightly higher around 37 degrees centigrade. Now they need to feed. There is nothing to eat on or around these barren rocks except seaweed and to get that they will have to swim. But the sea around here is surprisingly cold around 12 to 16 degrees centigrade and only the bigger iguanas can absorb enough heat to power the dives to enable them to go to the seaweed at any depth. However their bodies are now thoroughly warmed up. The thermal camera shows them as golden yellow as they clamber down over the cold blue rocks and dive into the sea. Although their islands lie almost exactly on the equator the sea here is permanently chilled by a cold current that sweeps up from the depths of the ocean so they won't be able to stay in the water for very long. They have no time to waste. In the shallows close to the shore the seaweed has been heavily cropped. To get a good meal they may have to dive to at least 12 feet five metres. They're able to reduce the chilling effect of the cold water by closing down the blood supply to their limbs and the outer part of their bodies. But even so their body temperature may drop by 10 degrees or so. A cooling like that would kill a human diver. After five to 10 minutes on the sea floor most iguanas have had enough and they return to the surface and the life-saving warmth of the rocky shore. A recently emerged iguana is black. It's chilled to the bone. Now they need heat in order to be able to digest that meal of seaweed and they get that by spread-eagling themselves on these black hot sun-baked rocks. The chemical process that produces the disgusting smell also creates heat and raises the temperature of the flower by up to five degrees above the surroundings sufficiently high for a lizard to warm itself on it on a cold morning. A cold windswept island off the coast of South Africa is not the first place you would go to if you were looking for reptiles. But here on Dassen Island among penguins and seagulls there is one of the greatest concentrations of tortoises to be found anywhere on Earth. There are about 2000 of them on this one tiny island. The penguins and other birds thanks to their warm blood are active no matter how cold it is but the tortoises have to wait for the day to warm up before they can get about their business. They bask in the sunshine powering up their bodies to the optimum working temperature of 33 degrees centigrade and then they go off to feed. As the day progresses the temperature raises quickly and even before noon it's too hot for comfort. The tortoises have to head for shade. In the late afternoon it gets cooler and the tortoises venture out again. For them this is the best time. They're thoroughly warmed up they've digested their morning meal and they've got energy to spare. The males begin to fight jousting like medieval knights using a projection on the front of the shell like a lance. The technique is to get the spike under your opponent and then flick him over onto his back. Contests can last for half an hour. The loser tries to right him but the winner keeps biting his legs. At last the victor loses interest and goes off to find the female who caused the argument in the first place. As for the loser if he doesn't manage to right himself soon he may cook in the sun. Tortoises are able to sunbathe out in the open because their strong bony shell gives them almost complete protection from predators. Less well-armoured reptiles like lizards are vulnerable of course to hawks and coyotes and foxes and cats. And in the morning when those warm-blooded animals are already active the lizards are cold and can't move fast. So they have a problem. But they also have a solution secret sunbathing. You really can't see them until you're right on top of them. And there's one there. I'm in Arizona and that at my feet is a lizard buried in the sand up to its neck. Even while it's buried it can use the sunshine to warm its whole body. It can control the supply of blood to its head so that it pools in a cavity behind the eye. Soon the blood there is as much as five degrees above the temperature of the rest of its body. Then the animal opens the major blood vessels in its neck and the hot blood circulates so that its whole body is thoroughly warmed even though it's still mostly below ground. This is a horned lizard and very beautiful too. As her body is the same temperature as her environment she can't heat her eggs by sitting on them as warm-blooded birds do so they're exactly the same temperature as the rocks beneath. After a couple of months both eggs begin to hatch. The first to emerge is a male. And the second will be too. It's the temperature which has determined that. If it had been a few degrees lower both eggs would have developed into females. Crocodiles have their sex determined by temperature in a similar way.


  BBC Life in Cold Blood Blooded Truth where reptiles and amphibians are sometimes thought of as primitive dull and dim-witted
 
In the Galapagos Islands some of the reptiles get their energy directly from sunshine
In the Galapagos Islands some of the reptiles get their energy directly from sunshine
  The tortoises have to head for shade
The tortoises have to head for shade
  A horned lizard and very beautiful too
A horned lizard and very beautiful too
  The jaw bone of a very large and very famous dinosaur
The jaw bone of a very large and very famous dinosaur
 
A baby North American painted turtle. It and the rest of its clutch have only just hatched. But it's late in the year and the chill of winter has already begun. If the hatchlings clambered out of their hole now they would find nothing to eat. So they stay where they are. The temperature will fall to minus 10 degrees. Ice crystals grow around the babies and even inside their bodies but their tissues are protected by a kind of antifreeze. This would kill any mammal or bird. They remain in this deep freeze for up to six months. But spring comes at last. The ice melts around them and eventually within them. Slowly they begin to come to life. It takes quite a time for them to become fully functional but eventually they're ready to face the outside world. So by allowing their bodies to cool they have avoided the hard times. With the arrival of spring their parents are now preparing to breed again. The male courts the female by gently strumming her cheeks with his long claws. And she responds. Cold blood is clearly no barrier to affection. In fact reptiles can conduct as complex and as sensitive a courtship as many a mammal. This is the biggest of all living reptiles and one of the most feared. If one creature were to be labeled a cold-blooded killer it would be this a saltwater crocodile a monster that can grow to a length of 20 feet six metres and weigh a tone. But male and female when they court blow bubbles at one another. He is three times her size and could easily crush her yet he treats her with great gentleness. He strokes her back. Slowly he aligns his body with hers. So union is achieved. Crocodiles are among the most ancient of reptiles. Their ancestors appeared at about the same time as the dinosaurs. But what about them? Were dinosaurs similarly cold-blooded? The rocks of the North American west are particularly rich in dinosaur fossils. A hundred million years ago this was a horizontal mudflat at the edge of a sea. And across it came an adult dinosaur with a smaller younger one trotting alongside leaving their footprints behind to be fossilized. They were iguanodons a herd them together with some bird-footed dinosaurs.     Were these all solar-powered? Some of the ancient reptiles had specific adaptations to help them collect heat. This is a plate from the back of a stegosaurus and you can still see the lines where the blood vessels ran which collected the heat and carried it to the rest of the body. So for the stegosaurus at least the need to collect heat seems to have been just as important as it is for its relatives alive today. But there are clues that suggest that ancient reptiles were better at maintaining their temperature than their modern counterparts. This is the jaw bone of a very large and very famous dinosaur. In life its head would have been 18 feet six metres above ground. This is the jaw of Tyrannosaurus rex. An animal as big as this has a very large body mass which retains heat very well. So perhaps these huge dinosaurs were in fact warm all the time simply because they were too big to lose all their heat overnight as a smaller reptile would. But what about when they were small? Were adolescent Tyrannosaurs able to maintain a steady body temperature? Were they in short warm-blooded? Evidence on that can be found in the microscopic structure of their bones. This is the leg bone of a young Tyrannosaurus and it has bands in it. The inner section formed when the animal was young has an open structure like the bone of a fast-growing warm-blooded mammal. The outer part is denser more like that of today's reptiles. But whether dinosaurs were really truly warm-blooded we may never know. What we do know however is that dinosaurs were extraordinarily successful and dominated the Earth for 120 million years. But there are some reptiles today that can keep their body temperature well above that of their surroundings and these are the tracks of one of them. The leatherbacks are the only reptiles in the world to have this kind of insulation. Her eggs laid she fills in the hole with sand. And now she's on her way back to the sea. Life in cold blood has been a great success. It has after all endured for some 320 million years. But how did it all begin?