Tortoise Breeding

Choosing the correct partnership

Most people overlook several critical factors where choosing the potential parentage is concerned, and yet amongst other aspects such as suitable nesting and incubation, it is one of the most important parts of a successful captive breeding program.

Firstly before embarking on any tortoise breeding project it is imperative that your chosen adult specimens are the same species and preferably subspecies.  This may sound fairly obvious to most but its surprising how many phone calls I’ve taken in my time from anxious humans concerned that their charges either aren’t fertile or that they’re encountering laying problems. Without exception the primary problems were usually associated with unmatched matings between distinctly separate species or subspecies.

Tortoises of different species should never be kept together or have access to each other.  As with all species on Earth different tortoise species harbour germs which themselves may be immune to, but which can turn pathogenic to others.  This risk increases tenfold when chelonia are expected to cohabit in captive situations even though they are from entirely different parts of the World.  In the wild an American Redfoot tortoise would never bump into a Tunisian F. Nabeulensis no matter how far it wandered and thus  from a bacterial, viral or parasitic view point never the twain shall meet either.  I cannot stress enough to new tortoise owners to stick to just one species unless be prepared for a disease which is waiting to happen.

In my pens I had a distance of several acres between the different species and even then my staff and I had to wear different clothes from entering one pen to another and we also walked our Wellington boots through farmers dip trays of strong disinfectant too.  In addition we never had bare hands.  From one pen to another disposable latex gloves were worn once and then thrown away.

The disease management program I had in place may sound completely over the top to the average hobbyist, and for most having a few acres between your pets is a ridiculous luxury, but when I was keeping and breeding hundreds of chelonia at a time it was an absolute necessity.

Apart from the possible outbreak of disease unmatched matings are hardly ever fertile anyway and will often lead to complications when egg laying due to odd shaped or odd sized eggs.
In short, stick to keeping the one same species whereby unnecessary problems and complications can be entirely avoided.

Although neonate hybridisation from matings of completely distinct separate species is an absolute rarity, and should be totally avoided anyway for the reasons I’ve already mentioned, the success with subspecies mating together isn’t always quite so critical in terms of failure or success.

In fact with certain species like Hermanns tortoises the two Eastern and Western subspecies Testudo Hermanni Boettgeri and Testudo Hermanni Hermanni will often interbreed very successfully in captive situations, although whether this should be encouraged is another matter to consider for the conscientious hobbyist as the Western species is becoming increasingly more endangered and true blood lines are becoming thinner within the pet industry.

Its the same with other species such as Horsfileds or Marginated tortoises. They will probably breed successfully between their own subspecies though again this means that distinct subspecies or races will become blurred.

However, with all the chelonia which fit into the so-called “Spur-Thighed” bracket (T.Graeca sp) it is far from plain sailing where successful mating is concerned. There are so many Northern African subspecies, along with distinctly separate (in my view) species originating from places like Turkey, The Balkans and so forth that unless you are a really keen specialist and can identify a subspecies with 100% certainty I would advise you not to attempt to simply breed from this group with a “hope for the best” attitude.  Afterall you wouldn’t expect a human to mate with a chimpanzee would you?

The best advice I can give to anybody looking to breed tortoises for the very first time is to choose either Hermanns or Marginated tortoises, and choose the male and females which look most genetically like each other in terms of size, carapace patterns, skin melanin and so on.  The more alike the parents look, the better your chance are of success.

 Preparing the adults

Once you’ve earmarked your male and female partners its essential for them to be both in tip-top condition when introduced to each other in order to produce viable offspring.

This very probably means preparing the chosen pair (or small breeding group) from the year before, as diet, calcium, UVB, day light levels and hibernation all have a profound effect on fertility rates.

During the preparation year any females should be kept away from any males and checked for any existing eggs which they may be carrying. The only true way of doing this is by a veterinary X-ray.
 If a female is found to be carrying eggs from previous encounters with males then she needs to be supplied with a suitable nesting ground, which I’ll talk about later.
Once the eggs have been laid, counted and checked, against the number of eggs present on the X-ray, then an extra period of 3 months should be given and the female then checked again, repeating the procedure until such time she is free of any eggs from previous encounters.

There are lots of articles on the internet about what to feed and what not to feed a Mediterranean tortoise, so I won’t go into too much detail here, suffice to say that both male and female tortoises should be fed a very good and varied diet consisting mainly of weeds and flowers, dusted with a good calcium and multivitamin powder.  In addition, access to extra calcium supplies should be catered for.  Smashed up chunks of cuttlefish bone are always a firm favourite amongst most tortoises and will be consumed readily, offering vital top-ups of calcium when needed.

Males and females should be housed (separately) outdoors as much as is physically possible during the spring and summer, and only brought inside or put under artificial lamps when the weather outside is cold and miserable.  Greenhouse accommodation can work really well in the UK allowing the tortoises to come and go as they please.
UVB is essential for the assimilation of calcium into the body so outdoor exposure is crucial, as are good quality UVB bulbs when indoors.

Presuming that during the preparation year the chosen pair or group have had a great diet, had access to plenty of sunshine and additional UVB, and have good calcium levels, then the next critical stage to get right is the hibernation method during the onset of winter.

Poor hibernation leads to poor fertility; this is particularly true of male tortoises. The testosterone levels and the sperm count of a male which hasn’t endured the best winter sleep is dramatically reduced when compared to that of a male which has had an unbroken restful brumation period.

Again there are lots of good advice on the internet in regard to the correct hibernation techniques of the Testudo sp of tortoise, so I won’t go into detail during this article. But by far the best method is the fridge method, whereby the temperature is controlled much more safely and accurately than the typical “box in a garage” method, and its this fridge method I used with all of my adults and babies alike, making use of second-hand commercial drinks chillers with large glass doors; the type you see in convenience stores full of Coca-Cola cans.

On awakening from hibernation the males and females should still be kept separately for the first few weeks to allow them to fully recover and get into full eating mode before mating.  Once the chosen male has had time to recuperate from his slumber and is active and eating well then it can be quite advantageous to introduce him periodically to another male, allowing them to fight and exert dominance over one another. Although it seems a rather unnatural thing for a pet owner to do, it actually boosts testosterone levels and consequently fertility levels too.
However please ensure that the males are only put together if they are of the same species, for reasons I spoke about earlier, and that all the males are in good general health.

Put the two rampaging males together in the same pen for an hour or two at a time, for two or three days prior to introducing the chosen male to the female, this will sufficiently boost testosterone levels and will encourage the males to fight for the courtship of a female.

The act of mating

So, after the preparation year and the successful hibernation, spring is in the air and its time for the testosterone-fuelled male to see his future conquest.

 Allowing them to be together for the first time and watching the two tortoises undergo courtship behaviour can be quite an eye opener, and also rather daunting, to the novice pet owner!
 The word “courtship” within the animal kingdom usually conjures up images of majestic dances, beautiful displays, and gentle wooing of the females.  However, within in the tortoise-world the “affection” couldn’t be any further from the truth.
The male will be extremely aggressive, ramming and shell-butting into the female like an armour-plated machine on the BBC’s production of “Robot Wars”.

 In fact the female will often be up-ended and rolled about on the ground like a defeated battle-tank at the hands of its more powerful and sinister adversary.   

The courtship, as if not aggressive enough with the never ending shell-butting, looks even more ruthless by the male’s attempts to bite any exposed limbs which aren’t pulled away fast enough from his attentions.

This ritual can go on for minutes or even hours at a time and so should be monitored carefully by the owner to ensure the female doesn’t become too stressed for too long.  Suitable pens with lots of hiding places are necessary, and also if possible the ratio of 1 male to 3 females can work well in terms of splitting up the attention.

Once the male has bullied the female into submission he will proceed to mount her.  During coitus the male, with his mouth gaping wide open, will vocalise his achievements through a series of high pitched squeaks. This is about the only time an owner will ever hear their tortoise actually make a vocalised noise, with the exception of the occasional disgruntled hiss when startled.

After two or three days of cohabitation the male and female should then be kept separately to each other, unless a small herd is housed together with a ratio of at least three females to one male.

A ratio of one male to one female is not a particularly good mix for extended lengths of time as the female will become stressed and the male too preoccupied with mating and dominance that he will often go off his food.

The gravid female

Once a tortoise has mated the eggs will be “shelled” with a hard layer of calcium, thus resembling small round chicken eggs.   Typically one single mating can fertilise up to thirty eggs, which are then shelled in clutches of between three to eight eggs at a time. And typically several clutches are laid several weeks apart until the eggs have all been laid.

Unlike humans where we have a set gestation period, a tortoise can choose how long to carry its eggs for, and when it should lay them.  This “choice” in real terms can literally mean anything from just a few weeks after mating through to an entire lifetime, for it is the suitability of the nesting ground that determines if and when a tortoise should lay.

Within my purpose-made pens my charges usually mated in early spring and laid from spring through until mid to late summer.

With a bit of experience you can often easily recognise when a gravid female is looking to lay.
She will generally go off her food for a period of time, anything from a few days up to a couple of weeks, and she will also start exaggerated exploratory behaviour of her habitat.

The exploratory behaviour often goes on for days, sometimes even for a few weeks, with the female marching up and down, backwards and forwards,  over and over again, in a seemingly aimless never-ending marathon of her enclosure. 

What she is actually doing is trying to find the perfect nesting site which offers the best chance of hatching viability. This behaviour whilst entertaining to watch is unfortunately pretty futile within the UK as our climate could never be suitable for successful natural incubation. However it is her hard-wired wild instincts which set her off in this pre-programmed quest.

If, after a few weeks, a suitable nesting site is not found then the tortoise will just retain her eggs until later in the year when a change of temperature and/or humidity may set the searching behaviour off again. And if no suitable site is found at that time then egg retention may take place until the following year with the procedure then repeating itself.

Although fertile eggs can still be viable after a year of retention the rate of success does diminish, and in cases where several years has gone by the viability of the eggs would be virtually nil.
Furthermore, due to the internal biology of a tortoise, extra layers of calcium will be deposited on top of the existing shelled egg as each season goes by, thus essentially meaning problematic and painful laying can occur due to over-sized or rough-textured eggs.  Prolapses can be common place if retention is prolonged, and also ruptured eggs can sometimes be observed too, which can lead to peritonitis and eventual death of the host.

It is therefore essential, as conscientious owners, to provide the very best nesting sites that we can possibly create, in order for our females to feel convinced enough that they will trust the future lives of their offspring with the chosen landscape.

Creating the perfect nesting sites

In the wild Mediterranean tortoises will chose a spot to dig their nests in sunny, south-facing positions, where the ground temperature is fairly constant at depths below the first few inches of substrate. The nesting sites are also usually on slopes or at the top of hills or mounds where the possibilities of flooding are completely negated.

In captivity we need to recreate these sunny slopes and mounds which not only look aesthetically genuine to our charges, but also feel and smell genuine to them too!

If the mound is too low the female will think it could flood, and furthermore she couldn’t excavate the nest to a sufficient depth. Therefore she will reject it.

If the mound is too dry, the female will presume the nest will collapse back in on itself, so she will reject it.

If the mound is too wet she will presume it could drown the eggs and so she will reject it.

If the mound is too hot she will presume it will “cook” the eggs, so she will reject it.

If the mound is too cold, she will presume the babies won’t develop, so she will reject it.

By now you may be thinking that trying to create suitable nesting sites in captivity is an almost impossible task, but in truth it is relatively easy, once you know the tricks of the tortoise-breeder’s trade, so to speak.

You may have noticed that I’ve used the words “nesting sites” (plural), not “nesting site”, for firstly the availability of several nesting areas will greatly increase the likelihood of successful laying, whereas offering a singular nesting site, and simply hoping it’s good enough for your gravid female, is a risk akin to having all of your eggs in the one basket, if you pardon the pun!

Ideally the best tortoise enclosures should have at least three nesting areas for the females to choose from.

Each nesting site should be a small circular mound of approximately 1 to 1.5 metres in diameter and at a sloping height of around ½ metre.  The mound should consist of a soft soil and soft sand mix of equal proportions, mixed together in a wheelbarrow or similar, with half a bucket full of water.

The consistency of the substrate when mixed together should be damp enough whereby you can dig a hole in it with your hand without the excavation falling in on itself, but not too damp whereby you can see or feel the water within the substrate or on your hand.

Once you’ve mixed it correctly and formed a sloping mound with the approximate aforementioned dimensions you then need to heat the mound up. By far the best method is to heat it from above with a high wattage lamp. I used to use 500W flood lamps on a suspended chain attached to a hook, which made height adjustment of the lamp very simple.

The temperature on the surface of the mound, directly underneath the lamp, needs to be approximately 35°c.

Due to the high running costs of such lamps, especially if you have a few of them hanging over various nesting sites, it is not advisable, nor indeed necessary to have them switched on 24/7.
In fact, rather pleasingly, the tortoises seem to prefer it if they’re not on all the time too, and will often choose to lay once the lamps have been switched off.  Therefore in my set-ups I used to switch the lamps on for two hours in a morning, and two hours in the early evening, as both times seem to trigger laying behaviour immediately afterwards. Whereas when they were left on during the hottest parts of the day we saw little reaction from the females.

Another observation, used especially for fussy layers, was the addition of a small rock of around 30cm in diameter and 15cm in height, which was positioned at the summit of the mound. This seemed to encourage even the fussiest of females to cling on to it with their front limbs whilst excavating with their hind limbs.  Also on occasions the simple addition of a piece of turf again positioned on the summit would sometimes trigger laying.

Once two or three days have elapsed the nesting sites may need spraying with warm water, and then hand-turned over with a small trowel, to add some humidity back in to the surface layers. Again this human activity can sometimes encourage new nesting behaviour from females seemingly attracted to the smell of the freshly dug earth.

The basic idea of having multiple sites is you can then set them up slightly differently; one with a rock, one with some turf, one slightly damper, etc, giving a female more choice to find what she is specifically looking for.

Once a female has settled on a spot she will start to dig the substrate with her hind legs, creating a pear-drop shaped hole of between 15 to 30cm deep. The excavating can vary in timescales, but on average we used to observe our tortoises typically taking between 5 minutes to 20 minutes.

Once excavated the female will then lay her clutch of eggs, which is usually in numbers of between 3 to 8.  Then she will re-fill the nesting hole with precision and care until eventually you wouldn’t even know that she’d been there at all. The egg laying and refilling again varies in time, but on average we used to observe 10 to 20 minutes on average.

It’s imperative that you thoroughly check all nesting sites every day by carefully digging around with your hand to feel for any eggs. Don’t rely on guess work or be fooled into thinking that a tortoise hasn’t used the facility that day, as their nest cover-up jobs are excellent at making fools of us.

Once you have removed the eggs from the nest you can allow them to sit at a cool room temperature for a day or two before transferring them into an incubator to warm them to the desired temperature.

Incubation

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. With my tortoise breeding farms we used very large home-made incubators made from insulated wood, with the temperatures controlled by precise thermostats rigged to large heatmats.

However, these days fully reptile-specific incubators, complete with temperature control to 0.5°c accuracy, and precise humidity control through self contained water pockets, are being manufactured and retailed at very reasonable prices and it’s these incubators I would urge you to use if you are at all serious about successful breeding.

Temperature

Mediterranean tortoise eggs can only successfully incubate if the temperature is between 26 to 34°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 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.

Humidity

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.

Egg Disturbance

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, if you were going to use a bird egg incubator rather than a reptile incubator it would have to be adapted so that it didn’t 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. 

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 100 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.

Hatching

Baby tortoises, when in the egg, are literally folded in half across their plastrons (underneath of their shells) 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 (shells) 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 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 egg 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. Tortoises from the same clutch don’t necessarily hatch together either, and 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.