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Tortoise Breeding & Incubation

One of the most rewarding and enjoyable aspects of tortoise keeping happens when your charges have offspring. Hatchlings emerging from their eggs, perfect minatures of their parents, yet seemingly even more adorable. Each one bringing proud smiles of joy to the faces of even the most experienced tortoise keepers....

However, captive breeding success has only quite recently been fully understood. Infact many enthusiast-level keepers had very variable results indeed. Some eggs seemed to hatch with very little persuasion, while others inevitably went rotten, collapsed or exploded in the incubator. In certain other cases, female tortoises suddenly became very ill or died during gestation or attempted egg-laying efforts. In this chapter I try to explain the reasons appertaining to hatching success, in the hope that more captive-bred tortoises will find their way into the European pet trade, thus diminishing the illegal wild-caught trade, still active due to an ever-popular demand for these "pets".

Courtship

Tortoises in the wild usually have stronger mating urges during the spring, after hibernation, through until mid-summer. Although this is somewhat dependent on the animals' geographical location. In some parts of the Mediterranean coastline, tortoises can often be found mating at chance intervals throughout the year.

The mating process begins with the male tortoise picking up a female's scent trail and following it until he ultimately reaches his target. Then the courtship begins.

Courtship techniques vary from species to species, but the common denominating factor between all of the Mediterranean group is aggresion. Unlike alot of the animal kingdom where partners are effectionately wooed by attractive and colourful displays, female tortoises are literally bullied into submission through relentless ramming, biting and butting from their male counterparts. The type of aggressive behaviour demonstrated by these amorous males varies between differing species, from biting and strange head-bobbing rituals of the Testudo Horsfieldii, to considerable and often wound inflicting biting and shell-battering from Testudo Ibera. The sickening thuds generated by this forceful butting can be heard from several metres away. Eventually, the female, after enduring bites on all of her limbs, will stop attemping to escape and retract into her shell. This is the cue for the male to mount her.

Male tortoises, when defending a territory from another male, will resort to this "courtship" behaviour, even including "mounting", but in this situation the ramming and biting is effectively used to dominate and ward off the offending male. In captive situations this behaviour is often misinterperated by the tortoises' owners, wrongly assuming their males are trying to mate with each other !

Mating

Once the male has climbed onto the females back, it succeeds in keeping it's stance by a combination of balancing on it's rear legs and by posessing a more concave plastron than the female.This allows the the curvature of the female's humped carapace to sit nicely underneath him. After finely adjusting his positioning, the male shuffles and wiggles his cloaca (tail), until his "ventral- opening" lines up with the females "opening." The male then erects his penis (known as a hemi-penis). This pushes through his ventral opening of the cloaca and enters hers. Ejaculation is followed shortly after, simultaneously accompanied by high pitched "squeaking" from the male. This is the only time that one will ever hear vocalised sounds made by a tortoise (except for the occasional discontented "hiss".) Interestingly each individual species generates a sound which is unique to their own kind.

The male usually mates with a female several times before finally letting her go free.

Gestation

One single mating results in up to 30 eggs being fertilised, although these will not be laid together in one clutch. Tortoise gestation is in fact quite remarkable with regard to the time scales involved, because the female can actually vary the length of the gestation period (from fertilsation to laying) depending on enviromental and nesting conditions. It is believed that tortoises can lay fertile eggs for up to four years after mating, although obviously fertililty reduces significantly after each season.

After fertilisation the tiny eggs are segregated into clutches of two to twelve, depending on species peculiarity, then , one clutch at a time are allowed to grow to full size. These full-size eggs are then "shelled", ready for laying, the egg shells being of similar density and appearance to a chicken's egg, - only smaller and more spherical. Once the pregnant female finds a suitable nesting area, sufficient to be able to incubate the eggs, she will proceed to lay the clutch.

Some weeks afterwards another stored clutch of fertile eggs will be allowed to grow to full size, be shelled and eventually laid . And so the procedure goes on until finally all of the eggs have been expelled. This can take a couple of years ...........all from one single mating ! Healthy tortoises normally lay two clutches per season, but in captive situations, particularly in the UK and Northern Europe, this is often highly unlikely, unless adequate artificially heated nesting areas are supplied .

Tortoises that don't have access to a suitable nesting area will not lay. Furthermore, each year that an egg is retained, it receives an extra layer of calcium. This causes severe complications due to the eggs becoming larger, lumpy and over-calcified , making any laying attempts extremely difficult (egg binding). In addition to this, retained eggs will on occasions erode through the oviduct walls, cause peritonitis and eventually lead to the animal's death . Successful surgery has been employed in some cases, with the over-calcified eggs being removed via a hole cut in the animal's plastron. However, this unfortunate situation can be entirely avoided by provisions being made for captive nesting.

Nesting & laying

Tortoises are very particular when it comes to choosing a suitable nest site. For incubation purposes they need to seek out a place which receives all-day sunshine and has very well drained earth. Consequently, south facing hillsides are often the favourite spots. Hillsides offer an advantage over flat landscapes , in as much as they're virtually flood proof , as obviously too much water would inevitably lead to the eggs being drowned. South facing sites offer extended sunlight hours, providing the essential warmth needed to attain a virtually constant day to night temperature several inches under the ground.

When nest-finding, tortoises actually nudge along the ground with their noses to check the temperature and soil type. The moisture content and soil plyability has to be correct or the nest would collapse, or be too firm to fully excavate. Once happy with a chosen site, then the long process of digging begins. The pregnant female digs downwards and outwards using long circular movements of her rear legs until a large bell -shaped hole is achieved. The depth required is approximately three quarters of the length of her shell. She then starts to lay her eggs one by one

Between the laying of each egg, she spends some time using her back legs to carefully roll the previous egg away from the "drop spot" to avoid two eggs cracking together. This also has the added effect of coating the sticky eggs with soil, lessening the breakage possibilities even further.

After the clutch has been laid she covers the eggs with soil, refills the nest and flattens it with her plastron.This is done to such a high standard that it becomes virtually indistiguishable from the rest of the surrounding landscape. This whole nesting procedure can take up to four hours to achieve !

The eggs are then left untouched to be naturally incubated by the steady soil temperature, this being around 30*c.

Captive breeding procedures

Suitable partners

We wouldn't expect chimpanzees to breed with gorillas, or hamsters to breed with mice, but it's amazing how many people presume one species of tortoise should be able to successfully breed with another. This is categorically not the case.

Simply putting any two tortoises together and expecting them to produce viable offspring is unrealistic, foolish, and detrimental to the animals' health. For example; an American Redfoot tortoise would never in it's life encouter a Turkish Ibera. They originate from completely different parts of the world and consequently are biologically alien to each other, each one carrying pathogens harmful to the other.

Incompatible matings rarely if ever produce fertile eggs. They do however cause unlimited health risks. Any eggs which happen to develop inside the female are very likely to be malformed, usually too large or mis-shapen to be safely expelled, this in turn can lead to peritonitis and death. Females which show any sign of distress when trying to lay or happen to lose movement in their rear legs, are demonstrating tell-tale signs of being egg-bound. In addition to pregnancy related problems, injuries are also often inflicted on the female during courtship, between incompatible species. For instance, a male Testudo Ibera would damage the shell of a North African Graeca during shell butting, because the "armour" of a Graeca's shell is considerably weaker than that of an Ibera's.

Also, the risk of disease transmission and viral infections are immense. Most species' immune systems aren't capable of fighting alien pathogens from any other species. As a result fatal viral infections are spread, often throughout a whole colony. There are dozens of cases each year where normally stable, long-term ,captive stock are all suddenly wiped-out within days of each other , simply because their owner has recently introduced a "newcomer". Another problematic factor is the "incubation" time of certain viral diseases. It has been known to take up to ten years for a deadly viral infection to display it's symptoms. One tortoise can look perfectly happy and healthy, yet be 100% deadly to another, due to carrying pathogens which itself is immune to, but which others are not. Because of these facts, it is so important to chose your breeding stock very carefully indeed. Pairs should be of the same species, and in the case of the "spur-thighed" group, the same sub-species too. Each animal should be seperately quarantined for at least one year before being put together to check for any health problems. This does not eliminate the risks entirely, but will help to significantly reduce them. It is also a good suggestion to check the tortoises' histories. Have they had any contact with another tortoise ? have they suffered with any illnesses or ailments ? has the female had any previous matings ? As already mentioned, a female can keep producing eggs long after any mating has took place, and will proceed to do so until all of the eggs from that mating have been expelled . This means that even after copulating with the tortoise you have intended her to be with, she may still be producing eggs from her last encounter, whether fertile or not. It is therefore wise to get the female x-rayed to check for any eggs. If she is carrying any they will show up extremely clearly on the x-ray plate. These will then need to be expelled either naturally or through artificial induction . Wait for another year and check again, and repeat until clear.

Another important requirement is to only select younger animals for breeding purposes, as they tend to be more fertile. In anycase, elderly females should not be subjected to the strenuous efforts and stress involved with mating and egg laying, as this often leads to ill-health.

When you have matched your perfect pair of tortoises (same species, same sub-species, free from previous eggs, young and perfectly healthy) you can proceed to put them together !

When introduced , the male will immediately demonstrate his aggressive courtship behaviour. This can go on for extended periods in captivity if adequate room is not employed to allow the female to escape. Actual copulation however is short-lived ,but may be repeated several times. It is recommended to keep the mating encounters brief by only placing them togther for a couple of hours a day for just a few days. This should be perfectly adequate for a successful fertilisation, but will lessen the chance of injury due to biting or butting.

Any open wounds should be treated immediately and the animals seperated, though this should be alot less likely to happen if the pair are suitably compatible in the first place.

After the mating sessions have taken place, females should be given access to higher than normal amounts of calcium to allow for proper egg formation and future hatchling well-being. This should continue until ALL the eggs have been laid.

Gravid behaviour

Gravid (pegnant) females typically display unusual and "unsociable" behaviour. This should prepare competent tortoise owners that their charges are ready to lay . The behavioural changes are usually a combination of the following :

*Restlessness ; Including exagerated exploritory behaviour. Constant climbing, digging, rambling, etc. This is often when tortoises can be found up-ended after falling from somewhere they normally wouldn't have been .

*Agressiveness ; Dominant behaviour , including butting, ramming, biting , even "mounting" , all of which are usually only seen in males.

*Not feeding ; Eggs take up an awful amount of space and push onto the stomach, supressing appetite. In addition, the pregnant tortoise's inflated hormone levels also contribute to the lack of appetite.

*Trial nest digging ; Captive females are often found digging shallow "trial" nests, presumably aborting full nest excavation due to an incorrect soil type. Tortoises, when they are at this stage, are ready to lay imminently.

As already mentioned, the consequences of a female retaining her eggs are unfavourable to say the least. So, adequate nesting provisions need to be made when a female starts to display the gravid behaviour patterns. If any doubt remains as to whether an animal is pregnant or not, then I would suggest taking the tortoise to a vet and getting an x-ray done. This also reveals the amount of eggs which are present, which can be helpful to know in the case of any laying difficulties or if the tortoise suddenly decides to expel some eggs in an unplanned area and you need to go find them !

Captive nesting conditions

If, like myself, you live in the U.K. or you're in a country with a similar climate, then the chances of "natural nesting" diminish considerably, due to the relatively inadequate strength of the sun. Consequently, artificial nesting areas mimicking near-natural conditions are required. The most efficient method I've found of achieving these conditions employs the use of an ordinary garden greenhouse or very large cold-frame....... Firstly any glass panels which could be in contact with a tortoise should be fenced off , thus preventing any unwanted accidents. A large load of diggable earth consisting of 40% sand and 60% top-soil is then mixed together in the centre of the greenhouse and heaped to form a mound with a depth of at least 18 inches and an overall diameter stretching several feet across. This is then lightly moistened to give it some plyability. An incandescent basking lamp should be hung directly above the mound at a distance from where a steady soil temperature of 30*c is attained. The greenhouse is then left like this for 12 hours a day, with full access for the gravid female to come and go as she pleases. This method will normally prompt laying within a couple of weeks.

If however you happen to own a rather fussy-layer, you could try another method which often seems to work when the more traditional green-house method doesn't : Find a box which the tortoise just fits snuggly in to, and fill it to a depth of at least 12 inches of the same sand & soil mix. Place the box in a completely dark room. Again hang a basking lamp above the soil to attain a steady 30*c, then place her in it. Do not have any other light source in the room apart from the one directly hung above her and leave her quietly alone. Incredibly , for whatever psychological reasons attatched to this method, it hardly ever fails ! However, please be careful with this method as the tortoise could overheat or dehydrate if left in the box for prolonged periods. If she hasn't started laying within an hour or so, she's not going to ! Finally, if neither of those methods work, then artificial induction is the only alternative. Take the tortoise to a competent vet and get it x-rayed. Count the number of eggs which are present and then inject the tortoise with a hormone called oxytocin. I have found one single shot of oxytocin is usually enough to make a tortoise lay within a couple of hours of bringing her home. But in cases where a tortoise has been kept on a calcium defficient diet, a five day course of calcium injections are recommended prior to the oxytocin shot, as this will help the tortoise to expel her eggs. After the hormone injection, place her in a box of soil and keep her warm . All of the eggs (which you have previously counted on the x-ray) should be expelled within minutes of each other, if not take her back to the vets the next day and repeat the procedure.

Although x-rays and oxytocin injections don't have any adverse effects on the fertile viability of the eggs, I believe natural egg laying methods should be encouraged first, as this is obviously less stressfull to the animal than a trip to the vets. It is also alot cheaper ! Once your animal has laid her eggs, carefully retrieve them and place them in an incubator as soon as is possible.

Incubation

Unless you live in a country which is home to a native species of tortoise, or is climatically capable of doing so, you are going to need to artificially incubate any eggs.

Methods ranging from keeping eggs in an airing cupboard, to floating them in containers in tropical fish tanks have been employed over the years with varying and mostly limited success.

At the time of writing the best incubation methods encorporate specialist shop-bought reptile incubators or adapted bird -egg incubators, although I will also list and describe some of the other, often commonly used, methods and their relative effectiveness . The reason some are successful and some are not is dependant on their capabilities of keeping the eggs in an enviroment which meets the three main criteria critical to success, namely ; correct temperature, correct humdity and nil disturbance.

Temperature

Mediterranean tortoise eggs can only successfully incubate if the temperature is between 25 to 35 *c. Below 25*c and the hatchlings won't develop, above 35*c and the develpoment would be far too quick, the moisture content would be lost too quickly and the hatchlings would die. Fluctuating temperatures of more than a few degrees can also lead to hatchling malformation or cause early deaths. Therefore a consistantly steady temperature or a temperature which is only allowed to alter by a degree or so is recommended. Most owners that I know tend to incubate their eggs at a steady 30*c as this is probably about the "safest." However, if you would like to specifically hatch a group of tortoises of the same sex , then this can be achieved by incubating at either a couple of degrees above or below 30*c, as sex determination in most Mediterranaean tortoises is dependant on the actual incubation temperature.

At 30*c the sex determination tends to be random, above this and you will normally hatch females, below 30*c and you'll probably get males. Although I personally wouldn't try incubating at temperatures over 32*c for risk of dehydration.

Humidity

The relative humidity required for the duration of the incubation lies somewhere between 50 and 90%. Unlike the temperature control, fluctuations in the humdity levels on a daily basis are not that critical, providing the overall mean percentage throughout the full period is within those guidelines. If the humidity is allowed to drop below 50% the egg contents would simply dry out . If allowed over 90% then the eggs would literally drown by absorbing too much water. I aim for an average of 75% which is achievable by providing small bowls of water that can be added to, or removed from the incubator accordingly. Temperature and humidity digital probes can be bought and placed in the incubator for very accurate readings.

Egg disturbance

Unlike bird eggs, a tortoise egg has to be kept the same way up after the first few days of incubation. It's yolk sack would smother the developing hatchling if it was turned upside down. Therefore before using any bird-egg incubators, they have to be adapted so they don't mechanically "turn".

Developing hatchlings also stress very easily, so handling should be kept to a minimum. I know a few breeders who regularly use a "candling torch" (a device used to illuminate the egg , making it slightly transparent to enable viewing of the embyo) but I think the risks involved with disturbing the egg are unnecessary and pointless and would I not recommend it. The less an egg is disturbed, the better it's chances will be of making it to hatching.

Incubators & their effectiveness

*The tropical fish tank

Eggs are half burried in a meduim such as vermiculite, within small plastic containers and floated in the warm water. This is a reasonable method for soft-shelled eggs, if the temperature is able to be turned up high enough, but the high humidity levels are far too great for Mediterranean tortoise eggs.

*The light bulb method

Eggs are fully burried in a container of moistened vermiculite, with a light bulb placed overhead to provide the heat. This is a very unreliable method due to temperature fluctuation, unless you are there 24 hours a day to change the wattage of the bulbs accordingly.

*The airing cupboard

Can provide heat from the hot water tank and humidity from wet towels etc, but is totally unreliable due to enormous temperature fluctuations.

*The heated seed propagator

Readily available at most garden centres, these can make quite a reliable incubator if used correctly. The built in thermostats of these propagators do tend to allow quite a bit of fluctuation, but if they are housed in a centrally heated room with a very stable air temperature, then they can work quite well. The eggs are half burried in a medium such as vermiculite within the incubator and small bowls of water are placed alongside to adjust the overall relative humidity accordingly. Only buy seed propagators with an adjustable heat control, otherwise they are factory pre-set at a temperature used primarily for seedlings, which is far too low for egg incubation.

*The shop-bought incubator

These are obviously the most reliable method. Reptile incubators are now being manufactured at reasonable prices, which allow full temperature control to within 0.5*c and precise humidity control through self contained water pockets.

Alternatively, bird egg incubators can be used, providing they don't rotate the egg. If you are thinking of adapting a bird-egg incubator, I would buy one that doesn't have "forced air" ventilation through means of a fan, as these tend to "dry out" tortoise eggs. Instead try to obtain a "still air" incubator ,which are more suitable for reptiles.

Which ever model of incubator you buy or build, the procedure of incubation remains the same: Gently place the eggs in the medium (vermiculite is often used and is readily available from most garden centres), not burrying the eggs more than half way. Adjust the temperature accordingly, and get it to remain as constant as possible. With the use of water bowls or pockets, adjust the humidity to between 50 and 90%. Finally, don't be tempted to touch or disturb the eggs until they have hatched or you know they are definately infertile ! It is hard to tell if an egg is going to be fertile or not, without egg-candling or egg-weighing, but due to the risks involved with these practices I wouldn't recommend them. I would simply suggest being patient and only disgard the eggs once they have become visibly obvious that they're infertile i.e. started to smell, imploded or exploded !

Incubation time

The time scale involved between placing your eggs in the incubator and seeing them hatch varies between differing species and the temperature they were incubated at. As a general rule of thumb anything between 50 and 150 days is applicable. The higher the temperaure the quicker they tend to hatch, but don't be tempted to incubate eggs at a high temperature simply to see them hatch sooner, as this will often lead to hatchling deformation or death.

Hatching

Baby tortoises, when in the egg, are literally folded in half across their plastron and are virtually round in appearance. When they have absorbed most, or all, of their life-supporting yolk-sack they start to straighten out. At this stage their tiny carapaces are pressed right up to the egg shell, which leaves an imprintment of the egg-shell texture on their carapaces. ( This can be seen clearly while they are hatchlings, until it eventually grows out.) Eventually they straighten out to such a degree that they puncture a small hole in the egg-shells with a bony protrusion which has developed on the end of their snouts, called an egg-tooth. The holes that the egg-tooth create help to weaken and dry out the shells allowing them to break open as the tiny tortoises emerge. The egg- tooth is only present for this job and will be worn away as the hatchlings grow.

Do not be tempted to interfere with the hatching process, unless it is plainly obvious that a tortoise is in serious trouble. Some tortoises escape from the egg within minutes of puncturing it, others can take a couple of days. Also tortoises from the same clutch don't necessarily hatch together either, I have know an example of three weeks between the first and the last hatchling to emerge safely !

Once they are free from the egg, it is a good idea to give them a luke-warm, very shallow bath, to wash off the sticky membrane surrounding them and to enable them to take their first drink