The Differences Between The Three Giants

 

   Many, many years ago, there used to be 12 different species of Giant tortoises around the world, some on each continent, except Australasia and Antarctica. Today we are reduced to 3 species and that is primarily because man sent them to extinction. Two of those remaining are classed as vulnerable and the largest, the Galapagos giant tortoise, is an endangered species.

 

The Sulcata or African Spurred Tortoise

 

   The smallest of the three, and some would argue that it is not a true giant, but it is still a formidable size, is the Sulcata tortoise of Centrochelys Sulcata. This is the largest mainland breed of tortoise, the other giants are both island species.

 

   The name Sulcata, comes from the Latin Sulcus meaning furrows, they are called this because of the large number of furrows on their shell. These guys originate in dry savanna, hot desert regions of sub Saharan Africa, although the pet trade has distributed them all over the world. This part of Africa is a hot, arid and hostile environment where only the strongest and fittest survive, to pass on their genes to the next generation. And surviving often means confrontation amongst the males, sometimes resulting in death, for the chance to breed with the females and allow their bloodline to live on.

 

   With the whole width of the continent to roam, these herbivorous giants are widespread and spend a lot of their time alone looking for food. There is not enough nourishment to live as a group, you find food for yourself, sharing might mean life or death and sometimes they have to go several days without eating or drinking.

 

   To combat the harsh conditions they have developed protection of pronounced, large, scaled, leg and body armour, which also helps prevent water loss from heat directly on their skin. They are like little tanks ploughing their way through the prikley shrubbery, that has evolved in the area to protect it and prevent it from being eaten to nothing in seconds. This creates pathways, through the brush, for other smaller animals to use too, so that they do not have to stray out into the open all of the time to move around. Seeds and foliage also snag on their shell and are propelled to new areas for propagation. They are powerful marchers, especially when the strong African sun has warmed their blood to temperature, and very little gets in their way, to stop them, they will just tramp right over the top of it.

 

   Sulcata Tortoises are a grazing animal, eating dry grasses and tough low growing foliage and succulents, they do not have the long neck of the other giants so their food source is concentrated at lower levels.

 

   Interestingly the pronounced pattern on the top of their heads, made from toughened scales, is as individual as a fingerprint and can be used to ID them.

 

 

 

The two pictures above are different male Sulcatas both aged about 15 years and you can see the difference in the  pronounced scale patterns on the tops of their heads. 

 

The picture below is of a female, of similar age, however, she has a much smoother head, her scales are much less pronounced becasue she does not get into battles like the two boys do.  Again, the patterning is different but it is much more delicate. - more like snake skin than crocodile,

 

 

 

   As mentioned they are fairly solitary animals, only usually coming together at breeding time around September to November and this is just after the monsoon rains, so there is plenty of food around and the adults are in peak physical condition. The Sulcata is polygamous, which means they try to mate with a number of females and this of course means that if more than one male is interested in a female there will be conflict. A testing of strength as they charge together, heads side by side in the oppositions neck cavity as they try to cause maximum damage to their opponent using their Gulars. These are hard, shell covered, bone protuberances, which jut out from the carapace, directly below their head. When they are not fighting they can use these Gulars to support their head whilst they sleep, a bit like a very hard pillow, but it means the can relax their neck muscles and sleep better. If they were to put their head and neck out, at full extension, like the other giants sometimes do when they sleep, it would leave them too vulnerable to attack from opportunistic predators.

 

   The inside of the neck cavity is probably one of the most vulnerable places on a Sulcata, the skin there is soft and leathery and it has none of the bone protuberances of the skin protecting their legs. They do not need them, if they are scared or under threat then they pull their head deep inside their shell and pull their forearms across the front of their face, with the effect of being a bit like closing two doors together. Their inner toenails on each arm (equivalent of their little fingers), hook into their shell at their arm pits like a locking mechanism and they are extremely difficult to pry apart, the best way is to wait them out until they relax and ‘open the doors’ but you could have a long wait. All body parts tuck in tightly for maximum protection, turning them into an oblong football. when younger, their Marginal scutes, the lowest ring of horny plates, around the bottom of their shell are much sharper than on other tortoises, in another form of predator defence.

 

   However, this leathery neck skin is no match for being stabbed with the Gulars and the intention is to rip the skin from where it melds with the inside of the shell, allowing the enemy to cause severed damage. Not only the trauma of the injury but the loss of blood in such a hot atmosphere invites infection and is a scent for other larger predators to follow. It also opens them up to the chance of fly strike, which is prevalent in such conditions. Injuries like this, out in the wild means almost certain death. It would definitely put the rival out of commission for mating with the female and that is all that the opponent cares about.

 

   In the fight to prove whoever is strongest there is a lot of pushing and shoving between the combatants. If you can’t injure them in the neck with Gulars, then the next best option is to stab them in the bottom with them. They are aiming for the Sciatic nerve which is located between the tail and the leg of the animal but is protected by conical shaped spurs on their back legs and thighs. It is these spurs that give it the other name it is known by the African Spurred tortoise. If this nerve is damaged then movement is much harder, sometimes the opposing tortoise is paralysed, sometimes permanently. For others its like you being given a dead arm by thumping it- puts it out of commission for a while but sensation eventually returns. The winning tortoise is not bothered which occurs, it just means that it is now longer a threat, the longer a fight goes on the more overheated the animals can get, which is not good for either of them.

 

   If the fight is particularly relentless then the males will try to overturn each other, which definitely makes the looser vulnerable. A tortoises lungs occupy the top of their shell and if they are rolled over onto their back then all of their internal body weight is pressing down on their lungs making it difficult to breath. So there is a very real chance they will die of asphyxiation. They will desperately flail their arms legs and head in the hope of rocking themselves and being able to self right, this is where shell condition plays an important part in their survival.

 

   An animal that has lead a healthy diet will have grown a smooth shell and will be able to rock side to side and hopefully gain enough momentum to roll to its side at the least and then hook a foot around something convenient and land right side up before fleeing for its life, in case the opponent tries it again. However, for those who have not had the healthiest of diets, it can lead to deformities of the shell known as pyramiding. This is when the bone underneath the Keratin shell has grown quicker and the Keratin scutes are forced upwards to cause the distinctive pyramid shapes. These pyramids act more like stabilising feet and prevent the animal from getting the rocking motion, so no matter how much they try their chances of success are severely limited and it is not uncommon for an animal in this position to die from a combination of dehydration, from the harsh African sun, and asphyxiation from the pressure on their lungs. Their only real hope of survival is if the enemy decided to ‘have another go’ at them, and inadvertently turns them right side up.

 

   Like all tortoises the female digs a hole and lays golf ball sized eggs before covering it over and leaving her young to sort themselves out. She can lay several clutches through the breeding season and may dig several ‘test holes; to make sure she is certain she has selected the right spot before finally committing to laying the eggs and it will take up to 180 days to incubate, as usual sex is controlled by the temperature, the hotter it is the more females are produced.

 

   It is very tiring for the female to dig the hole and she will usually do it in the early evening when it is coolest. They do an amazing job of digging it out to the depth that they want just using their back legs,which means they can only feel what they are doing, without actually being able to see what’s happening behind them. If they break off digging and turn around then they run the risk of disturbing the spoil stacked precariously at the side of the hole and filling it back in, thus wasting their previous effort. The hole is usually about the size of a rose tree plant pot and will be the maximum reach of her back legs deep. When she is satisfied she will take a few moments to recover before she actually lays the eggs. All of this digging helps her internal muscles manoeuvre the eggs into the correct position for birth. Once she starts laying it happens quite quickly, popping out one after the other, each one is covered in a protective slime for ease of passing and to help cushion them as they land in the hole, she does not want the breaking after all of that effort.

 

   Approximately 20 eggs later, she snaps out of the trance like state that she had been in during birth and hurriedly begins to fill the hole back in. After covering it over and pressing the earth down firmly, with her body weight to disguise the nest, she leaves them to it, her job is done, she then goes off to find somewhere away from them to rest and recover. However, she does not completely leave the area, she will hang around for a day or two to protect the nest, which makes sense as she has put a lot of effort both into digging it and the precious cargo held inside. She wants to make sure that all of her hard work is not dug up. After a couple of days the smell of her presence and activity will have dissipated, and it is safe for her to move on to pastures new.

 

   Sulcata are VERY good at digging holes, for other reasons too, the female uses their back legs for nest building but both sexes uses their powerful front arms to dig tunnels and caves to get out of the scorching midday sun. In their natural environment, they are Crepuscular, meaning they are mainly active at dawn and dusk. The rest of the day when there is very little shade for their protection, from the harsh African sun, they have little choice than to go underground. They are formidable diggers, it is unbelievable how much soil they can dig in a small space of time. They would probably beat you, if you tried it using a shovel, especially when the angle got more inaccessible to us, as the hole does not go straight down. They use both front legs and fling the dirt back behind them, the same movement as turtles swimming. This means that it is out of their way and they don’t have to move it again and if the debris that lands on them, it acts as a natural sunscreen to protect them as they are working.

 

   Temperature below ground can be several degrees cooler and damper, so despite the effort involved, it is worth it, to help stop them becoming dehydrated in the sun, and sometimes they can go down to 10 feet underground. It also works the other way too, if the nights in the desert are particularly cold then their burrows are at a slightly higher temperature than outside.

Sometimes they will just make the hole the depth of their body and use it as a brief stop over but other times they will excavate deeper and make more frequent use of this burrow. When they are not using these burrows other animals move in and use them to escape the harsh temperatures so you could call them the house builders of the Sahara.

 

 

 

 

 

   When it is excessively hot outside they can go into what is known as Estivation, which is a type of stasis. It means that their body slows right down and uses very little energy and they will rest and remain there in the safety of their burrow until the outside world cools to a more tolerable level, this can be days or weeks in extreme cases. It is very much like the smaller breed tortoises going into hibernation over winter.

 

   However, when the rains come and food begins to grow once more they can eat and drink almost 15% of their body weight in one sitting, to make up for the times of fasting. 

 

   With the lack of water in the Sahara mother nature has come up with a interesting solution. Instead of when they drink or take moisture from anything that they eat, which is where they get most of their fluids from, the water does not just pass through their body once and then be expelled in the form of urine. Instead they cycle it through their system on more than one occasion so that they can take maximum precious water content from it. The result is that they produce Uric Acid instead of conventional urine. This Uric Acid is a thick paste like consistency, looks very much like cottage cheese, or toothpaste, in fact. Unfortunately, if they are not able to get sufficient water then this ‘cottage cheese’ can become very dry and impacted, making it very difficult to pass and has the knock on effect of causing kidney problem for the animal. Unhappily, they do not have access to medical IV drips out in the wild, so they just have to hope that they can hold on until the rains arrive and they can drink their fill and fully rehydrate their systems.

 

   An adult male Sulcata will weigh up to 91kg and will be 24-36 inches, as usual in most of the animal kingdom, the females are smaller at around 20 inches and 36 kg.

 

   Thanks to the pet trade there are many Sulcata tortoises around the world being kept and bred by enthusiasts. However, in the wild the loss of their natural habitat, being used as target practice and older animals being taken by poachers, for the pet trade and medicinal uses has left these fascinating animals vulnerable and teetering on the edge of extinction.

 

 

 

Samson with an adult male Sulcata

- don't forget Samson is not yet full grown, he will get just under a third bigger than what he is now.

(That is a third longer, a third wider and a third higher too, so that is a lot more growing still to do!)

 

 

 

The Aldabra Giant Tortoise

 

 

   Some Aldabra Giant Tortoises, Aldabrachelys Gigantea, are naturally as large as, or even larger (in individual cases) as Galapagos Giant Tortoises but they have been classified as the second largest tortoise in the world.

 

   These prehistoric looking reptiles were a large species of tortoise before they even made the crossing from the islands off the east coast of Africa, to land on and claim another small coral, volcanic island in the Seychelles, which explores named after them, The Aldabra Atoll. It is thought that a pregnant female was probably the first to arrive, after being washed away from one of the other Islands in the Seychelles, during bad weather and floating on the current. This ‘Aldabra Eve’ would be the ‘mother of tortoise’. No doubt she was not the only one to have made the unexpected journey in the long history of the region but she would have been the one that started the colony off.

 

   This was a very harsh environment with large oceans surrounding it so there was no easy escape, which meant the tortoises had to evolve to be more tolerant of each other, than other mainland species, as there was only so far that they could get away from each other. They have become non territorial and dislike confrontation and aggression, and unlike other species of tortoise they are more selfless and content to share food and space. Large mature animals will happily spend time coexisting, alongside youngsters without them having to be blood related, unlike many other species.

 

   On a physical basis Aldabra tortoises have a few differences to the Galapagos species, and they are a separate species. It is not the case that they started out in the same area and just spread further apart, going to different sides of the world and just evolving slightly differently.

 

   The Aldabras shell is much thicker than the Galapagos. They have a Nuchal Scute, which the Galapagos don’t, this is their smallest scute, or shell plating, and it is positioned on their shell right above their head. Aldabran heads are smaller and no wider than their neck, which is long to maximise their reach for food and nourishment. The distance from nostrils to mouth is much less in Aldabra tortoises and it is more rounded between the snout and the top of the head which slopes up and backwards, whereas the Galapagos is virtually flat on top head. I always think that Aldabras have more raptor like features, whereas Galapagos are more snake looking.

 

 

 

 

   The Seychelles has a wet season and a dry season, so there can be many months when they have to go without fresh water. Temptingly, their Island may be surrounded by water but as it is sea water it is not suitable to drink. The sea is also tidal and floods over part of the land creating tidal pools which the animals go and sit in to cool down, when the water retreats so do the animals, huddling under the sparse vegetation of bushes and shrubs and anything else that can offer them shade.

 

   Aldabras have thick skin and carapace to help them traverse over the sharp volcanic tundra in search of the meagre food supply that grows there. Like the Sulcata they are also architectural landscapers, knocking down trees and bushes to get through and distributing seeds and foliage both through eating it and passing it out through their poo, in new territory, and by things sticking to their shells, and being dragged along until they fall off, it is the way many plants procreate on that island as there are few other animals specie live there, it is too far from the main land for many to make the journey without needing to stop on the way and there is now where but the sea to stop and land. Unless they encounter a passing ship.

 

   Aldabra tortoises are opportunistic vegetarians. This means that their main diet is plants and grasses but if they came upon a dead fish or bird then they would happily scavenge from it. They would also cannibalise dead tortoises too, it is a harsh environment that they live in and it would be a shame to let such a good source of protein go to waste, due to squeamish sensibilities. They occasionally indulge in small invertebrates, especially the babies as it is a good source of protein to help them grown strong. There is very limited fresh water available on the island, outside the rainy season, so they have to get most of their moisture from their food, in whatever form they can.

 

   Males are much bigger than females, a difference of maybe 100kg or more. Like all other tortoises, after breeding the female digs a hole in the sand to lay her eggs, mostly on the beach, above the water line so the don’t get washed away, but there are not many options on their hard, volcanic, Atoll. Interestingly it depends on how many other tortoises live in that area as to how many eggs she will produce. There is no point in overcrowding the area or everyone will starve. Again, she has nothing to do with the babies once she has laid them, they come out a miniature but fully formed individuals capable of looking after themselves.

 

   Adults have no predators except from man, their greatest danger of death is to dehydrate in the hot sun, if they fall asleep too deeply in the wallow and do not notice when the water retreats and they get stuck in the mud, it would be like cooking a jacket potato!

 

   If they have the misfortune to fall down one of the crag holes in the island, and they are injured or unable to get out, then they will die of starvation, no one is coming to save them.

 

   With youngsters, their main predators, besides sailors, would be birds of prey or rats, which are an introduced species, probably by accident from the sailing ships. Sometimes, the birds would fly up into the air with them and then drop them from height and split their shells open so that they could feast on the flesh within.

 

   There are also crabs, that come from the sea, to prey on the youngsters, as they hatch, so early life is hard and not all will survive but as long a one does then she has done her job. In the past many of these tortoises were taken aboard the old fashioned sailing ships so that they could be kept alive, in the hold of the ship, for many months without needing more food and water and this enabled the sailors to have fresh meat on a long voyage, thus improving their own diet and health. Aldabra tortoises also store a lot of water in their bladder so they would be kept by the sailors for use as emergency water rations too!

Luckily Aldabra has a coral sea bed surrounding it which makes it very difficult for ships to land, there are only a couple of places that give access to the inside of the island. This is probably what saved this animal species from extinction here. The sailors found it too difficult and treacherous to navigate their way through on a regular basis, once they had captured and removed the easy pickings. So they took to plundering animals from other, easier to access, areas and the Aldabra Giant Tortoise was free to continue living in its own little world.

 

   That is not to say that Aldabra population was not greatly affected by these practices, hundreds of animals could be taken with each visit. However, it is not an easy island to walk across and especially if you are lugging a 100-200kg tortoise with you, which you then have to struggle to get in and out of your dinghy before winching it up onto the sailing or whaling vessel. All the while being conscious that the lagoon water could retreat from under your vessel several times a day when the tide went out.

 

   As they are top of the food chain, on the Atoll, they do not need to have formidable amounts of armour, like the Sulcata, and thus they do not need to be able to pull fully into their shells to hide. This means that they have developed more fat pads around the arms and legs to fill out these vacant cavities so they can look much more ‘chubby’, as if they are spilling out of their shell. They do have strong thick back legs, reminiscent of elephants feet with chunky toe nails on the ends for grip, for hauling their bodies up and down the sides of the volcano as the try to find fresh foliage. The thick scales offer maximum protection against injury from the jagged terrain underfoot. At the front, they weirdly walk on their wrists with their hands turned in, but it works for them!

 

   Due to the tortoises intense feeding habits many plants on Aldabra have evolved so that their seeds are now no longer produced from the top of the plants but much closer to the ground instead so that they can avoid the tortoises close cropping mouths. The ‘tortoise turf’ that they graze contains 20 plus different species of grasses and turf and many have become naturally dwarfed by the grazing pressures of these giant reptiles.

 

   

   These tortoises are much more relaxed animals because they don’t naturally worry about things coming to attack them and are often content to sprawl out, in the sun, and sleep with arms, legs and neck at full extension, in the ultimate vulnerable position.

 

   Studies show no real advantage to how they curl their head around, they do it in both directions. Often it just seems to be personal preference at the time, what is most comfortable, or maybe offers a slightly different temperature, a bit like us sleeping on our left or right side when in bed.

 

   The youngsters are energetic and can move quickly especially if they perceive danger. The adults are more lumbering, walking at around a slow human walk, but when you consider the size of the adults, when they take a stride they cover quite a distance in one go, so they make faster progress than you may expect.

 

   Aldabras can be quite lazy, they don’t seem to actively chase females like other species do, it seems to be more a case that if a female who takes their interest is passing then they will try to mate with her. However, it does not take much, just the chance of some fresh food, to distract him and let her get on her merry way. They don’t seem to have the drive to breed that other tortoises do, maybe it is because they live so long at potentially 150-200 years plus, they are more content to let nature take its course and it will happen when it happens. As long as they have at least one successful hatchling, born with their genes in it then they have duplicated themselves and the line will live on into the future.

 

   In 1982, the Aldabra Atoll was designated a UNESCO Marine World Heritage Site, thus protecting the tortoises from further disturbances of human influences and plundering. Strict control of visitors is enforced, to limit the number to a minimum, and very few people have been allowed ashore since. Unfortunately, Aldabra is located near to one of the busiest shipping routes in the world and modern man is now threatening the islands not by plunger but by contamination, from oil spills.

 

   Being a volcanic island parts of it are mere metres above sea level and if something like a Tsunami struck, or the sea levels continue to rise, thanks to climate change, it could wipe out most of the islands population, of around 150,000 tortoises, and other precious wildlife, in one go. History shows that it has happened several times in the past and there is no doubt it will happen again, it may not be next Tuesday afternoon, or even this century but it is just a question of when?

 

   Although Aldabra is their home island, smaller populations of Aldabrachelys Gigantea, exist on Fregate Island in the Seychelles and on Moyenne Island in the Sainte Anne Marine National Park where they are popular visitor attractions. The conservation parks on Mauritius and Rodrigues breed these animals and it is from here that most of the UK Aldabras have been imported from. There is also an Isolated population on Changuu near Zanzibar.

 

 

The Galapagos Giant Tortoise

 

  Many people have heard of the Galapagos Giants, they are the largest tortoises in the world. They are also the ones featured in the titles of the BBC TV show 'One Foot In The Grave'. They are the 13th heaviest reptile alive today.

 

   However, they are probably most famous because it was on the Galapagos Islands that Darwin studied their abundance of species in the 1830’s and worked on his Theory Of Evolution By Natural Selection.

 

   This is also where the infamous ‘Lonesome George’ the Galapagos Giant Tortoise, and the last living member of his subspecies, from Pinta Island, lived and became senonimous with conservation efforts, until he died on June 24, 2012 at The Charles Darwin Research Station on Santa Cruz Island. Despite numerous attempts scientists were unable to get George to breed with any of the females that they introduced him to. Lonesome George, was once describes as the world's "rarest living creature". Thanks to his notoriety, he left a big impression on a lot of peoples lives and the Galapagos giant tortoise has now become a flagship species for conservation efforts throughout the Galapagos and the world.

 

   Galapagos is situated on the equator and is around 900 km (560 miles) off the west coast of South America, being a part of Ecuador. San Cristóbal, Santa Cruz, and Isabela, are the three most populated islands but many of the islands are protected as part of Ecuador's Galapagos National Park and Marine Reserve. It is a very different area of the world to the Aldabra Atoll, which is off the east coast of Africa.

 

   It was formed approx 3 million years ago and was settled by tortoises probably about one or two million years ago. At that time, the Aldabra Atoll was still not even above the surface of the ocean – thus Galapagos tortoises have existed 20 to 50 times longer than Aldabran tortoises!

 

   The Galapagos Islands were first discovered by Europeans on 10^th March 1535 when a ship on its way to Peru drifted off course and found the islands which were so barren that 2 men and 10 horses died of lack of fresh water. They saw "such big tortoises that each could carry a man on top of himself." The Islands first appeared on a map around 1570 when Spanish explorers claimed it, and named it Galapago meaning tortoise.

 

   Galapagos is a collection of 21 volcanic Islands, in the eastern Pacific Ocean, rather than just one specific place. Nearly each Island had its own subspecies of Giant tortoise, often with different characteristics, developed over time to help with life on that Island. Like Aldabra, Galapagos is also a popular place for the green sea turtle and other distinctive and exclusive species.

 

   Again, like on Aldabra, when man came to the archipelago the managed to introduce Goats and rats to the region, which severely damaged the natural ecosystem. Unlike Aldabra there came a sustained and permanent human presence, which has expanded over the years putting greater pressure both on the limited space and on the native wildlife, including the lives of the giant tortoises. In the 1930’s an airport was built, there are now 3 servicing the Islands and although recent efforts have been made toward using renewable energy they still handle around 300,00 visitors each year to the Islands

 

   Although these two giant tortoises, the Aldabra and Galapagos, share many similarities and characteristics, they are also very unique in their own ways. They have both survived by inhabiting former volcanic islands, in large oceans and evolved to cope with the harsh environments and habitats this creates.

 

   One significant difference between the two species is that Galapagos tortoises evolved into giants after they arrived on their islands, growing so large to fill a niche position in the local animal kingdom but the Aldabra tortoises were giants before their ancestors arrived on their Atoll. Even so the Galapagos tortoise would have probably still been considered large tortoises by today’s standards. Its not like they were a little Hermann making the 1000 km journey to their new homeland. Large tortoises would have had a greater chance of surviving the journey, over water from the mainland , for such a distance as they can hold their heads a greater height above the sea level. Their significant water and fat reserves would be important to allow the tortoises to survive the long ocean crossing without food or fresh water, and to endure the drought-prone climate of the islands when they first arrived.

 

   All subspecies of Galapagos tortoises evolved from common ancestors that arrived from mainland South America by overwater dispersal. It must have happened this way because Galapagos is volcanic in origin and has never connected to the mainland. So, they must have reached Galapagos by water, possibly by rafting on tree branches, as currents transported them up the coast of Chile and Peru before circulating westward. Genetic studies have shown that the Chaco tortoise of Argentina and Paraguay is their closest living relative but it is not a direct ancestor and is much smaller. The split from their common ancestor probably happened 11-25 million years ago.

 

   Survival on the 1000km oceanic journey is accounted for because the tortoises are buoyant, can breathe by extending their necks above the water, and are able to survive months without food or fresh water. As they are poor swimmers, the journey was probably a passive one, facilitated by the Humboldt Current, which diverts westwards towards the Galapagos Islands from the mainland.

 

   Naturalist Charles Darwin remarked after his trip in 1835, "These animals grow to an immense size ... several so large that it required six or eight men to lift them from the ground".

 

   The largest recorded individual, Goliath,  reached a weight of over 400 kg and length of 1.37 meters, width if 103cm and stood 69cm high. Like most animals, males are larger than females — adult males weigh around 272–317 kg, while females are 136–181 kg. The Saddleback subspecies is at the smaller of these size ranges, probably due to the poor quality, and amount of, vegetation available to them.

 

   The Galapagos Archipelago is a mixture of tropical savanna and semi arid climate which becomes a tropical rainforest environment as you move further into the Northwest areas. Most of Galapagos is covered with semi desert vegetation of shrublands and grasslands and dry forest but the higher land is usually green and lush with some tropical woodland and the lower levels have more arid conditions with area of barren volcanic rock and thorny shrubs and cacti. These differences in environment have made the tortoises evolve different shell shapes to make the most of their feeding opportunities.

 

   During the rainy season which is from June to November it can drizzle for days and dense fog can conceal the Islands giving a surreal feel. Temperatures by the sea are down at 22 °C where there can also be a steady wind, blowing from the south. The other six months is the warm season where temperatures rise to 25 °C and there is no wind at all. It is sunny at this time, apart from strong sporadic downpours. It is generally still wetter in the highlands on the slopes of the volcanoes because of the condensation and fog. In the coldest time of the year it will get down to 10°C.

 

   The giant tortoise are native to seven of the Galapagos Islands with shell size and shape differing between the subspecies and populations. On Islands where it is humid in the highlands the tortoises are larger, and grazers, with domed shells and short necks, looking much more like an Aldabra tortoise. Whereas, on islands with dry lowlands the tortoises are smaller and flatter with ‘saddleback’ shells arching up over the neck, and their neck is a lot longer too. This allows them to stretch up and browse the trees and overhanging foliage as another source of food.

 

   The tortoises are herbivores with a diet of cacti, grasses, leaves, lichens, local fruits and milkweed. Juvenile tortoises eat an average of 16.7% of their own body weight in dry matter per day. They get most of their moisture from the dew and sap in the vegetation allowing them to survive longer than 6 months without drinking water. They have a very slow metabolism and can endure up to a year when deprived of all food and water, surviving by breaking down their body fat to produce water as a by product. When thirsty, and water is available, they may drink large quantities very quickly, storing it in their bladders and the "root of the neck" On arid islands, tortoises lick morning dew from boulders, and the repeated action, over many generations has formed half-sphere depressions in the rock.

 

   Some tortoises have been observed to exploit a mutualistic relationship with the Galapagos Finch who will actively seek to groom them. After the tortoise rises and extends its limbs, the bird may go beneath the tortoise to investigate, harder to reach areas for parasites, whereupon suddenly the tortoise withdraws its limbs to drop flat and kills the bird. It then steps back to eat the bird, presumably to supplement its diet with protein. It seems to be learned behaviour and it is also something that Aldabras sometimes do with their native bird life.

 

   Although, at one stage Charles Darwin thought that these tortoises were deaf they are not, it is just a case that tortoises depend far more on vision and smell senses than hearing senses.

 

   Like the Aldabara Giant Tortoise the Galapagos Giant Tortoise does not have any natural predators, except for man. In the 16^th century there were around 250.000 tortoises but by the 1970’s that had plummeted to just over 3000. This was because of the meat trade and the ever encroaching of man into their territory and all that entails. This directly caused the extinction of the tortoise population on at least 3 Islands.

 

   These Giant Tortoises have a large bony shell usually a dull brown or grey colour with a a characteristic scute pattern on their shells, which they keep throughout life. Lichens can grow on the shells of these slow-moving animals and seeds and fauna are distributed in this way across the Island. The legs are large and stumpy, with dry, scaly skin and hard scales. The front legs have five claws, the back legs four and they help it grip as it climbs to the higher feeding areas.

 

   The tortoise can withdraw its head, neck, and fore limbs into its shell for protection. The Galapagos species have developed into two different forms, the domed variety are usually larger and better at resisting the cooler temperatures that can occur in the high elevations, on the sleeping volcano which created the island.

 

   In comparison the saddlebacks occupy smaller islands less than 500m in elevation where habitats are drier and food more scarce. They have developed longer limbs and necks, as well as altered the front of the carapace to increase vertical reach, which allows the tortoise to get to taller vegetation too. When a saddleback tortoise withdraws its head and forelimbs into its shell, a large unprotected gap remains over the neck, this gives clear evidence of the lack of predation during evolution, or it would not have developed in such a way. Saddlebacks are more territorial and smaller than domed varieties. The saddle shape may have another purpose, in that it allows the males to put on a greater display of dominance when in competition for a female. They could rely on the impressiveness of a greater vertical neck height rather than body size. The saddle back males are definitely more aggressive than their domed male counterparts.

 

   A Galapagos tortoises head is more angular, and virtually flat on top. It looks a lot more like the head of a snake, and it is wider than the width of the neck, rather than an Aldabra, which has a head no wider than its neck and has a more raptor like quality.

 

 

 

A Galapagos tortoise at the Charles Darwin Research Station.

 

 

   Like most tortoises, Galapagos Tortoises are cold blooded and need to bask for 1–2 hours, after dawn, to absorb the sun's heat and then they will begin actively foraging for 8–9 hours a day. They have been observed to walk at a speed of 0.3 km/h (0.2 mph).

 

   On the larger and more humid islands, the tortoises seasonally migrate between low elevations, which become grassy plains in the wet season, and meadow areas of higher elevation (up to 2,000 ft (610 m) in the dry season. The same routes have been used for many generations, creating well-defined paths through the undergrowth known as "tortoise highways". On these wetter islands, the domed tortoises are gregarious and often found in large herds, like Aldabras can live. In contrast to the more solitary and territorial disposition of the saddleback tortoises. In fact they can be very territorial and view their space and food as their own property, often fighting to defend it. They have a sense of self and will warn others off. They will often cause injury to each other as a result.

 

   Tortoises sometimes rest in mud wallows or rain-formed pools, both as a way of cooling down and rehydrating, as well as gaining protection from the assault of parasites such as mosquitoes and ticks, which can be dislodged by taking dust baths in loose soil. Some tortoises have been noted to shelter at night under overhanging rocks or sleeping in a snug depression in the earth or brush called a "pallet".

 

   Sexual maturity is at around 20-25 years in captivity and around 40 in the wild. Mating can occur at any time of the year but is most often between February and June which is during the rainy reason in the humid uplands. At breeding time males will face off in a ritualised display of dominance which involves rising up on their legs and stretching their necks up to full extension with their moths gaping in an effort to look as big as possible. Sometimes head biting occurs with animals of similar size but usually the smaller tortoise will back down ceding mating rights to the victor. this behaviour is more typical with the saddlebacks, which are more aggressive and have longer necks.

 

 

 

Galapagos Tortoises At The Reasearch Station On Their Home Island

 

 

   Mating can be very aggressive, as the male forcefully rams the females shell with his own and nips at her legs. During actual mating the male vocalises with hoarse bellows and grunts. This echoes the behaviour of some of the smaller breeds of tortoises like the Mediterranean Spur-thighed Tortoise and Marginated Tortoise species. The rhythmic groans of mating is one of the few vocalisations that tortoises make.

 

   When it is time to lay the eggs in July to November the female can have to travel several kilometres to find the nesting areas on the dry sandy coast. Once she has dug the hole out, using her back legs she will lay up to 16 eggs that are about the size of billiard ball and can weigh from 82-157 grams. The domed species average 9.6 per clutch whereas the saddlebacks are less at only 4.6 per clutch. Again, like with all tortoises, temperature controls the sex of the hatchlings. Lower temperatures produce boys, and higher produce girls. The lower temperatures will also take longer to hatch than eggs laid in the hot season. This means global warming will influence the greater production of female tortoises and could eventually lead to a shortage of males, with the extreme chance of making the species die out.

 

 

Galapagos Tortoise harchling

 

 

   The hatchlings emerge after 4 to 8 months and weigh only 50 grams, which is about 5 times heavier than a baby Herman tortoise. The 6cm baby must dig its way to the surface after it has managed to get out of its shell. This can take several weeks, thankfully their egg sac can sustain them for several months. In particularly dry conditions the hatchling may die underground if the soil is too hard for them to claw through, whilst flooding of the nest areas can drowned them. There is no difference in appearance between the domed species and the saddle back Galapagos when they are born. For the next 10-15 years they will inhabit the lowland areas before branching out to explore their Island further.

 

  Excessive heat stress or being crushed by falling rocks or falling into cracks are some of the natural hazards they will have to combat. Whereas, the Galapagos Hawk, feral pigs, dogs, cats and black rats are the animal predators out to get them.

Between the 1790s and the 1860s, whaling ships and fur sealers systematically slaughtered and captured thousands of the Galapagos tortoises, in far greater numbers than the buccaneers preceding them. Some were used for food but from the late 19th century onward, many more were killed to extract their high-grade "turtle oil", for lucrative sale to continental Ecuador. While their diluted urine and the water stored in their neck bags could be used as emergency drinking water for the ships crew.

 

  A total of over 13,000 tortoises being taken is recorded in the logs of whaling ships between 1831 and 1868, and an estimated 100,000 were taken before 1830. Since it was easiest to collect tortoises around coastal zones, females were most vulnerable to depletion during the nesting season. These hunters were responsible for the extinction and decimation of most of the Galapagos subspecies of Giant Tortoises.

 

  Population decline accelerated with the early settlement of the islands in the early 19th century, leading to unregulated hunting for meat, habitat clearance for agriculture, and introduction of non native predators such as rats and cats

Galapagos tortoise exploitation dramatically increased with the onset of the California Gold Rush in 1849. Tortoises and sea turtles were imported into San Francisco, Sacramento and various other Gold Rush towns throughout Alta California to feed the gold mining population.

 

  Scientific collection expeditions took 661 tortoises between 1888 and 1930, and more than 120 Galapagos Tortoises have been taken by poachers since 1990. Once they were becoming more and more scarce, people began to pay to have them in their collections, as well as being put into museums. Threats continue today with the rapid expansion of the tourist industry and increasing size of human settlements on the islands The tortoises are down from 15 different types of subspecies when Darwin first arrived to the current 11 subspecies, and one of those is extinct in the wild.

 

  In 1835 when Darwin’s the Beagle departed from Galapagos there were over 30 adult tortoises, stacked up and stored in the lower deck, as a source of fresh meat for the Pacific crossing. Their shells and bones were either thrown overboard or used to as something to carve for board sailors.

 

  Captain Porter who was with Darwin on this voyage described those from Hood Island, as having their shells in front thick and turned up like a Spanish saddle, while the tortoises from James Island are rounder, blacker, and have a better taste when cooked. The 17th-century English pirate, explorer, and naturalist William Dampier wrote, "They are so extraordinarily large and fat, and so sweet, that no pullet eats more pleasantly," whilst Captain James Colnett of the Royal Navy wrote of "the land tortoise which in whatever way it was dressed, was considered by all of us as the most delicious food we had ever tasted." The  US Navy were similarly impressed as Captain David Porter declared, "after once tasting the Galapagos tortoises, every other animal food fell off greatly in our estimation ... The meat of this animal is the easiest of digestion, and a quantity of it, exceeding that of any other food, can be eaten without experiencing the slightest of inconvenience." however, Darwin himself was less enthusiastic about the meat, writing "the breast-plate roasted with the flesh on it, is very good; and the young tortoises make excellent soup; but otherwise the meat to my taste is indifferent."

 

  The Galapagos Giant Tortoise is now strictly protected and is listed at the highest level of Appendix I of the Convention on International Trade in Endangered subspecies of Wild Fauna and Flora aka CITES.

 

  In 1936, the Ecuadorian Government listed the Giant Tortoise as a protected subspecies. Within the archipelago, 14-15 subspecies of Galapagos tortoises have been identified, although only 12 survive to this day. Five are found on separate islands; five of them on the volcanoes of Isabela Island. Several of the surviving subspecies are seriously endangered.

 

   In 1959, it declared all uninhabited areas in the Galapagos to be a national park and established the Charles Darwin Foundation. In 1970, capturing or removing many subspecies from the islands was banned, which included both live tortoises and their eggs. 

 

  To halt trade in the tortoises altogether, it became illegal to export the tortoises from Ecuador, captive or wild, continental, or insular in provenance. The banning of their exportation resulted in automatic prohibition of importation to the United States too.

 

  In an effort to make up for mans previous plunder, 20^th century conservationists have released thousands of captive bred juvenile animals onto their ancestral home islands in the hope that they will successfully repopulate them. Breeding and release programs began in 1965 and have successfully brought seven of the eight endangered subspecies up to less perilous population levels.

 

  Scientists have started using trackers to identify their migration routes and nest sites so that they can be better protected. The GNPS and CDRS operate a tortoise breeding centre on Santa Cruz Island , where young tortoises are hatched, reared, and prepared to be reintroduced to their natura habitat. Eggs are collected from threatened nesting sites, and the hatched young are given a head start by being kept in captivity for four to five years to reach a size with a much better chance of survival to adulthood, before release onto their native ranges. One male Galapagos Tortoise, Diego, who is a captive animal has fathered over 800 eggs, he has been so sucessful that he has now been retired from stud.

 

  Researches believe that the total number of animals in the wild now exceeds 19,000 but they are still classed as an endangered species. However, this is a great improvement from the 1974 census where there was a mere 3060 individuals.