One of the most rewarding and enjoyable aspects of tortoise keeping happens when your charges have offspring.
However, captive breeding success has only quite recently been fully understood. In fact many enthusiast level keepers had very variable results. 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.
Tortoises in the wild usually have stronger mating urges during the spring, after hibernation, though until mid-summer. This is somewhat dependant on the tortoise’s 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 on a female’s scent trail and following it until he ultimately reaches his target. Then courtship begins.
Courtship techniques vary from species to species, but the common denominating factor between the entire Mediterranean groups is aggression. Unlike other parts of the animal kingdom where partners are affectionately wooed by attractive and colourful displays, female tortoises are bullied into submission though 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 head bobbing rituals of the Testudo Horsfieldii, to considerable and often wound inflicting biting and shell battering from Testudo Ibera. Eventually the female after enduring bites on all of her limbs, will stop attempting 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.
Once the male has mounted the female, it succeeds in keeping the stance by a combination of balancing on his rear legs and by possessing a more concave plastron than the female. This allows the curvature of the females humped carapace to sit nicely underneath him. After 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”) 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 to go free.
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 regards to the time scales involved, because the female can vary the length of the gestation period (from fertilisation to laying) depending on the environmental and nesting conditions. It is believed that tortoises can lay fertile eggs up to four years after mating, although fertility reduces significantly after each season.
After fertilisation the tiny eggs are segregated into clutches of two to twelve, depending on the species, 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 are a similar density and appearance to a chicken 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 fill size, be shelled and eventually laid. The procedure continues until all of the eggs have been expelled. This can take a couple of years – all from one single mating. Healthy tortoises usually lay two clutches per season, but in captive situations this is often unlikely, unless adequate artificially heated nesting areas are supplied.
Tortoises that don’t have access to a suitable nesting area will not lay their eggs. 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 difficult (egg binding). In addition to this, retained eggs will on occasions erode through the oviduct walls, cause peritonitis and eventually lead to the tortoise’s death. Successful surgery has been employed in some cases, with the over calcified eggs being removed via a hole cut in the tortoise’s plastron. This unfortunate situation can be avoided by provisions being made for captive nesting.
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. South facing hillsides are often favourite spots for nest sites. Hillsides offer an advantage over flat landscapes; they’re virtually flood proof, as too much water would cause the eggs being drowned. South facing sites offer extended sunlight hours, providing the essential warmth needed to attain a virtually contact 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 pliability has to be correct or the nest would collapse, or be too firm to fully excavate. Once the female is happy with a chosen site she will begin the long process of digging. She will dig 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 will then start the 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 indistinguishable from the rest of the surrounding landscape. The 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.
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.
Simply putting two tortoises together and expecting them to produce viable offspring is unrealistic, foolish and detrimental to the tortoise’s health. For example, an American Redfoot tortoise would never in its life encounter 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 mating 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 misshapen to be safely express, 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 the 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.
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 10 years for a deadly viral infection to display its symptoms. One tortoise can look perfectly happy and healthy, yet be 100% deadly to another due to carrying pathogens which it is immune to itself, but others are not. It is important to choose your breeding stock very carefully. Pairs should be of the same species, and in the case of the Spur-Thighed group, pairs need to be the same sub species too. Each tortoise should be separately quarantined for at least one year before being put together to check for any health problems. This does not eliminate risks entirely, but will help to significantly reduce them.
Another important requirement is to only select younger tortoises for breeding purposes, as they tend to be more fertile. 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 for the female to escape. Actual copulation is short lived, but may be repeated several times. It is recommended to keep the mating encounters brief by only placing the tortoises together for a couple of hours a day for just a few days. This should be perfectly adequate for a successful fertilisation, and will lessen the chance of injury due to biting or butting.
Any open wounds should be treated immediately and the animals separated.
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 (pregnant) 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:
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 that the female is pregnant or not, we suggest taking the tortoise to a vet and getting an x-ray done. This will also reveal the amount of eggs that are present, which is helpful to know in the case of any laying difficulties or if the tortoise decides to expel some eggs in an unplanned area and you need to go and find them!
In the UK the chances of “natural nesting” diminish considerably, due to the relatively inadequate strength of the sun. Artificial nesting areas mimicking near natural conditions are required because of this. The most efficient method of achieving these conditions employs the use of an ordinary garden greenhouse or very large cold frame. Firstly, any glass panels that could be in contact with a tortoise should be fenced off, preventing any unwanted accidents. A large load of 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 across several feet. This should then be lighting moistened to give it some pliability. An incandescent basking lamp should be hung directly above the mound at a distance from where a steady soil temperature of 30°c can be achieved. The greenhouse will then be 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 you do happen to have a fussy layer, you could try another method which often seems to work when the more traditional greenhouse method does not. Find a box that the tortoise fits quite snugly into and fill it with at least 12 inches of the same sand and soil mix. Place the box in a completely dark room, and again hang a basking lamp above the soil to attain a steady 30°c, and then place her in it. Do not have any other light source in the room other than the lamp hung directly above her and leave her quietly alone. Incredibly, for whatever psychological reasons attached to this method, it hardly ever fails. However, be careful when using 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!
If neither of these methods work, then artificial induction is the only other alternative. Take the tortoise to a competent vet and get her x-rayed. Count the number of eggs that are present and then inject her with a hormone called oxytocin. One single shot of oxytocin is usually enough to make the tortoise lay within a couple of hours or bringing her home. In cases where the tortoise has been kept on a calcium deficient diet, a five day course of calcium injections are recommended prior to the oxytocin shot. 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 should be expelled within minutes of each other, if not take her back to the vet the next day and repeat the procedure.
Methods of incubation 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.
The best incubation methods incorporate specialist shop-bought reptile incubators or adapted bird-egg incubators. The reason some are successful and some are not is dependent on their capabilities of keeping the eggs in an environment which meets the three main criteria to success: correct temperature, correct humidity and nil disturbance.
Mediterranean tortoise eggs can only successfully incubate if the temperature is between 25 to 35°c. Below 25°c the hatchlings won’t develop, above 35°c and the development 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. A constantly steady temperature or a temperature that is only allowed to alter by a degree or so is recommended. Most owners 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 Mediterranean tortoises is dependent 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 will normally hatch males.
The relative humidity required for the duration of incubation lies somewhere between 50 and 90%. Unlike the temperature control, fluctuations in the humidity 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 to reach over 90% then the eggs would drown by absorbing too much water. It would be best to aim for 75% humidity, 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.
Unlike bird eggs, a tortoise egg has to be kept the same way up after the first few days of incubation. The 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 that they down mechanically “turn”.
Developing hatchlings also stress very easily, so handing should be kept to a minimum. Some breeders regularly use a candling torch (a device used to illuminate the egg, making it slightly transparent to enable viewing of the embryo) but the risks involved with disturbing the egg are unnecessary. The less an egg is disturbed, the better its chances will be of making it to hatching.
Incubators and their Effectiveness
- The Tropical Fish Tank – Eggs are half buried in a medium 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 humidity levels are far too great for Mediterranean tortoise eggs.
- The Light Bulb Method – Eggs are fully buried in a container of moistened vermiculite with a light bulb placed overhead to provide heat. This is a very unreliable method due to the 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. This method 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 buried in vermiculite within the incubator and small bowls of water are placed alongside to adjust the overall relative humidity accordingly. Only bus 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 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. It would be best to purchase a “still air” bird egg incubator as these are more suitable for reptiles than “forced air” incubators. The eggs are gently placed and half buried in vermiculite. 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%. Do not touch or disturb the eggs until they have hatched, unless you know that they are infertile. It is hard to tell if an egg is fertile or not without egg candling or egg weighing, but due to the risks involved with these practices it’s best to be patient and only disregard the eggs if it becomes obvious they are infertile i.e. started to smell, imploded or exploded.
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 temperature the quicker they tend to hatch, but don’t be tempted to hatch the eggs at a high temperature simply to see them hatch sooner, as this will often lead to hatchling malformation or death.
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 imprint of the egg shell texture on their carapaces. This can clearly be seen 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 creates 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 jib 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. Tortoises from the same clutch don’t necessarily hatch together either, it has been known to take up to three weeks between the first and last hatchling to emerge safely.
Once they are free from the egg, it is a good idea to give them a lukewarm, very shallow bath, to wash off the sticky membrane surrounding them and to enable them to take their first drink.