Reptile care info

Care and Captive Breeding of the Gidgee Skink, Egernia stokesii stokesii. Text and photos by Sascha Knauf

 

Long since the days of unrestricted export of Australian flora and fauna, captive breeding of Australian skink species has become established, although the supply of these lizards does not come close to meeting the great demand for them. With few exceptions, captive breeding of Australian skinks is practically problem-free as long as seasonal cycles are strictly maintained. This article reports specifically on the care and breeding of one species: the gidgee skink, Egernia stokesii stokesii.

Taxonomy

According to WILSON and KNOWLES (2000), the genus Egernia (the spiny-tailed skinks) comprises a total of 26 species, all but one of which are endemic to Australia and Tasmania. The species of Egernia can be further classified into seven groups, each named for the taxon that typifies it:

Egernia cunninghami-group

Egernia striolata-group

Egernia kingii-group

Egernia luctuosa-group

Egernia whitii-group

Egernia major-group

Egernia rugosa-group

Egernia stokesii belongs to the Egernia cunninghami-group, which includes a total of seven species of medium-sized to large skinks with strongly keeled scales. The tail is robust and covered with spiny scales, which the members of this group utilize in their characteristic defensive behavior.

Egernia stokesii is divided into four subspecies: the nominate Egernia stokesii stokesii (Gray, 1845); Egernia stokesii aethiops Storr, 1978; Egernia stokesii badia Storr, 1978; and Egernia stokesii zellingi (De Vis, 1884).

The common name "gidgee skink" is Australian. This species is also commonly known as the spiny-tailed skink. The species name is in honor of Admiral John Lort Stokes, an accomplished officer of the British Royal Navy who was serving on the HMS Beagle, under the command of Robert FitzRoy, when Charles Darwin made his famous voyage. The subspecies name "aethiops" basically means colorful (referring to the darker coloration), and the subspecies name "badius" comes from the Latin for reddish brown (STORR et al., 1981).

 

 

Housing in a group: a mated pair with one of their offspring

 

 

 

 

 

These skinks hide in crevices and block the entrances with their spiny tails to protect themselves from enemies. Pictured is a 2-year-old male                                                                                                  

Description of the nominate form

Egernia stokesii stokesii is a medium-sized skink. The male reaches an average of 230 millimeters in total length; the female, 220 millimeters. COGGER (2000) gives the snout-vent length as 180 millimeters. In my own observation, there is usually a small but visible size difference between the sexes, the males being a little larger, but this is not grounds enough for positive sex- ing. In general, it is very difficult to distinguish between the sexes on the basis of external appearance. With experience and much observation of behavior, however, one can make a reasonable guess about whether a skink is male or female.

The nominate form of the gidgee skink has a chocolate- brown dorsal ground color, which can vary greatly in intensity from one individual to another. Reddish-brown specimens are also common. The limbs are often somewhat darker than the body. Small groups of beige, sand-colored, or sometimes white scales form spots at regular intervals along the body, and less on the head. Single black scales are also present. The pattern varies greatly between individuals, and depends on the patterns of the parents. Some specimens have a uniform coloration with no spots at all. The undersides are a light cream color.

The body is generally cylindrical and plump with strongly double- keeled dorsal scales. The tail is short, stocky, and somewhat dorsoventrally flattened - it is also extremely muscular and bears pines of up to a centimeter in length.

In general, this skink is well adapted to its environment and has a very imposing appearance.

Distribution and habitat 

COGGER (2000) very generally describes the distribution of Egernia stokesii as being from the western coast to central and southern Australia; and also in southern Queensland and northwestern few South Wales.

More specifically, Egernia stokesii stokesii is found on the Houtman Abrolhos Islands, Western Australia (COGGER, 2000; HAUSCHILD and GASSNER, 1995; WILSON and KNOWLES, 2000). Egernia stokesii badia is found in south- western Australia. Populations have been described from Dirk Hartog Island in Shark Bay. The “eastern form” described by WILSON and KNOWLES (2000) said to be found in South Australia, western New South Wales, central Queensland, and southern Northern Territory. HAUSCHILD and GASSNER (1995) extend this distribution to include part of central Australia, and cite the species in all Australian states except Victoria. Egernia stokesii aethiops is known from Baudin Island in Shark Bay (COGGER, 2000; WILSON and KNOWLES, 2000). For the distribution of Egernia stokesii zellingi, COGGER (2000) gives eastern Australia.

These skinks all occupy similar habitats, with some variations across the vast range of the species. In general, the lizards habit areas with narrow crevices into which they can wedge themselves tightly for shelter from enemies. Egernia stokesii stokesii and Egernia stokesii aethiops are found mainly in limestone outcrops. Egernia stokesii badia, on the other hand, often prefers hollow dead tree trunks and limbs (WILSON and KNOWLES, 2000).

In a land with such extremes of climate, the choice of shelter is critical for the necessary thermoregulation of a reptile. Rock heats up quickly and holds warmth better than wood. Wood provides better insulation. In any case, the skinks often have little choice, and take refuge wherever they can.

Behavior 

Hardly any other lizard group exemplifies as well as these skinks how perfectly anatomy and behavior can be adapted to habitat - and knowledge of the gidgee skink’s natural behavior is necessary for providing captive housing suitable for the species.

Egernia stokesii is very strongly territorial, and carries out practically all of its activities within its territory. This includes morning basking directly in front of its shelter. This species is strictly diurnal, and its daily activities in the wild correspond directly with the rhythm of the sun - and in the terrarium, with a suitable lighting regime.

The gidgee skink begins its day inside its night shelters. As soon as the morning sun (or terrarium lamp) has warmed the environment sufficiently, the skink emerges from hiding to bask until it reaches its preferred body temperature. After a long sunbath, the skink begins searching for food. It forages for vegetation, always staying within close proximity to the basking spot and shelter. Midday is spent digesting. If the day is too hot, the skink retires into its shelter. In the evening it forages again, tending to venture farther from the shelter than during the morning feeding. The day ends with the final rays of sunlight. Like some of the other species of the genus, Egernia stokesii tends to always defecate in a certain area of its territory. In the wild, this behavior can leave clear evidence of the presence of a nearby hiding place (HAUSCHILD and GASSNER, 1995) - and as regards predator avoidance, the reason for the behavior is not clear (GREER, 1989; COGGER, 2000). Coprophagy (eating feces) is common (pers. obs.), and serves to enrich the intestinal flora of the animal and increase digestive efficiency. Juveniles in a group eat specifically the feces of adults (pers. obs.).

If danger is perceived, the skink runs to its shelter as fast as possible. Once inside, the skink inflates its body by inhaling deeply, and blocks the entrance with its spiny tail - this posture makes it practically impossible for an enemy to pull the skink out (HAUSCHILD and GASSNER, 1995; GREER, 1989; COGGER, 2000; pers. obs.). Based on other species - e.g., Egernia kintorei or Egernia multi-scutata - it may be assumed that Egernia stokesii also prefers shelters with at least a second entrance (GREER, 1989), which should be taken into consideration when planning a terrarium.

In intraspecific combat, the gidgee skink lashes sideways with its powerful spiny tail, sometimes even with the rest of the body inside the shelter (pers. obs.). Territorial combat occurs not only between males, but also with unfamiliar females, and follows a specific routine. Threat displays include gaping with the mouth, inflating the body, and turning sideways. If the threat displays are not successful, the skinks resort to biting on the flanks, legs, and tail. If a confrontation reaches this stage in the terrarium it is a real problem because there is usually no way for the losing skink to escape. These skinks are merciless, and fighting continues until one of the rivals is killed or flees - in the terrarium such a battle usually ends in death.

But be careful. Mating behavior in Egernia stokesii is practically as violent as territorial fighting. The male is not at all gentle with the female. Many elements of combat behavior are also seen in mating behavior.

Life within the family group contrasts starkly with the violent territorial behavior. Several individuals often peacefully share the same shelter (HAUSCHILD and GASSNER, 1995; GREER, 1989). This can also be observed in the terrarium. Juveniles can even be raised together with their parents. The adults are clearly protective of newborn offspring. Unusual among reptiles, this species shows a mother-child relationship (MAIN and BULL, 1996). Under certain circumstances, behavior between unrelated skinks is different from behavior between related skinks.

However, the harmony within a group can change abruptly when juveniles, especially the males, reach sexual maturity and have no opportunity to establish their own territory. Conflicts generally arise between the father and his grown sons. In order for natural social behavior to be observed in captivity, the enclosure must provide sufficient space. Oppressed individuals should be removed from the group and housed individually for a recovery period before being housed together with others of its species. Who is housed with whom is a question of feeling. Usually mated pairs are the best cohabitants.

 

 

Portrait of a male

 

 

 

 

 

Housing 

At the time of this writing I have 12 gidgee skinks: two mated pairs with offspring, and a group of juveniles. All are housed in wooden terrariums that measure 80 x 60 x 100 centimeters. The lower side and back walls are covered with plaster and used by the skinks for climbing. The substrate on the bottom is sand. Several heavy flat slabs of rock are stacked such that, together with the back wall, they form a system of crevices and galleries with more than one entrance. Large dead limbs complete the furnishing.

 

 

One of the author's terrarium setups. Ideally the back wall should be made of rock, but that was unfortunately not possible in this case for technical reasons. The entire top is covered with wire mesh, which, in conjunction with fans, provides optimal ventilation.

 

 

 

Overall lighting is provided with an 80-watt HQL lamp following the photoperiod illustrated in Figure 1. A spot lamp hangs just in front of the rock slabs to create a basking spot. The bulb is changed depending on the season. In spring and autumn a 25- to 40-watt bulb is sufficient; in summer I change to a 60-watt bulb. Another spot lamp can be mounted over a different exposed part of the enclosure. The skinks often bask together, climbing on and over each other even though there is plenty of space for both of them. An Osram 300-watt “Ultra Vitalux” lamp is used for 20 minutes a day to provide UV radiation, which the skinks readily bask in.

Figure 1: Hours of daylight per day adapted to central European conditions. This daily lighting regime has proved successful for raising gidgee skinks over a period of years. The gray bars represent the winter rest period. From the middle of November until the middle of February, the lights are turned off. Within a period of 2-3 weeks, hours of daylight drop from the shown to zero.

Under the spot lamps, the temperature reaches about 45°C (113°F). Overall cage temperature is generally maintained with these lamps, but a heat cable is also set under the substrate for use when necessary. Ideally a heat cable should be set underneath the floor of the terrarium (this protects the lizards in case any toxic fumes are produced from overheating).

Small water dishes are always available for the skinks to drink from. Air circulation is created with a ventilation system. The fan speed can be controlled to provide just enough air movement to avoid stagnant air but not produce draughts - vital for the health of the skinks.

In spring, the entire enclosure is lightly misted with warm water every day for a week, in the morning just after the lights are turned on. Thereafter spraying is reduced to every other day, and then 2-3 times a week in summer. The sprayed water should dry up within a couple of hours. In autumn I spray only very occasionally, especially when shedding begins. In winter, the terrarium is kept completely dry. This is important since dampness during overwintering can contribute to fungal infections that can be fatal.

The room in which the terrariums are set up is very light, and it is easiest to keep the Australian lizards under the conditions of Northern Hemisphere seasons. Since only captive-bred specimens are legally acquired, there is no problem of adaptation.

Egernia stokesii likes to climb a lot, and must be given the opportunity to do so in the terrarium. Stone- or plaster-covered side and back walls are good for providing additional climbing surfaces. If live plants are desired, grasses or hardy bushes are best, or even small eucalyptus trees, depending on the size of the enclosure.

Identification of the sexes 

As already mentioned, the sex of a gidgee skink cannot be positively identified on the basis of external appearance alone (HAUSCHILD and GASSNER, 1995: pers. obs.). We can distinguish between invasive and non-invasive methods for identification of sex. The method chosen by the keeper will depend on time available and the health of the animal - non-invasive methods are preferred.

A practical method for determining the sex of an individual (that is sexually mature!) is to place a known male adult into the enclosure with the skink of unknown sex. If necessary this can be done with a known female adult. By carefully observing the behavior of the two skinks together - aggression, copulation attempts, etc. - you can determine the sexes with an accuracy of about 85 percent (personal experience). This works only with animals that are really adults - i.e., at least 3 years old.

Massaging the cloacal region can produce eversion of the hemipenes, but if this does not happen you still don't know if the animal is male or female. This method takes skill (that comes with practice), and cannot positively identify a female, but it may be useful in conjunction with observing behavior.

The method of probing used for sexing snakes cannot be used in spiny-tailed skinks. The tail of the skink is so muscular that the probe could not be inserted without enough force to damage the sex organ.

Endoscopy is a method of sexing that is 100 percent accurate (SCHILDGER, 2000), but it has drawbacks. The body cavity must be opened, which requires that the animal be anesthetized. This is most practical with the larger species of skink. An advantage is that other organs can be inspected at the same time. Conversely, if an endoscopic examination is indicated for medical reasons, the sex of the animal can be verified at the same time.

A more elegant method of sexing a lizard is by DNA analysis. This has been done for years with birds. The invasive aspect of this method is drawing blood or taking a tissue sample. As is commonly done with other lizards, blood can be drawn from the ventral tail vein - this should be done by a person with experience.

Care and breeding 

Keeping and breeding Egernia stokesii requires adherence to a clear maintenance regimen. Seasonal changes must be marked in order to trigger the natural yearly cycle of the animals. In this way, reproductive behavior is synchronized among breeder specimens. Also, the winter rest period is necessary for restoring the general health of the individuals. The following should be provided:

Breeding is usually also successful under less rigid maintenance conditions (HAUSCHILD and GASSNER, 1995), but problem animals can usually be conditioned to reproduce if raised with these points taken into consideration.

In addition to the benefits for reproduction, annual cycling also generally increases the well-being of the animals. Remember that the biorhythms of the lizard are determined by the dynamics of their environmental conditions. Even captive-bred animals show behavior important for survival in the wild, such as hibernation, when temperatures and light (intensity and duration) decrease. The winter rest period corresponds with a time when food is scarce and temperatures and sunlight are insufficient for maintaining a body temperature necessary for activity. However, it is also important as a period of physiological conditioning and restoration, so should be part of the annual cycle in captivity as well.

After the winter rest period, when day length and temperatures increase in spring, the captive- bred gidgee skinks soon begin mating activity. The male follows the female around the terrarium. Biting on the tail and flanks is meant to keep the female from getting away, and to stimulate her receptivity. Meanwhile, the male continually attempts to gain a grip on the female’s neck. In his courtship biting the male seems to be quite brutal, but this is apparently normal behavior for this species. Even receptive females are bitten, and the bites may draw blood - these wounds generally heal well without medical treatment. Bite wounds on the neck of the female are often the first sign that copulation has taken place (HAUSCHILD and GASSNER, 1985; pers. obs.).

Offspring are born about 3,5 (HAUSCHILD and GASSNER, 1985) or 4 months (pers. obs.) after successful copulation. Much has been published regarding litter size for Egernia stokesii stokesii. MAIN and BULL (1996) report a total of 53 offspring born to 12 females in litters of 2-7 (average, 4.4) babies each between 18 February and 30 March 1994. It should be noted that all of these females were taken from the wild between December 1993 and February 1994, namely the same season as the births - meaning that they had copulated in the wild. They had been kept in outdoor enclosures until the end of February (end of summer in the Southern Hemisphere). In any case, these litter sizes are about the same as what I have observed in terrarium breeding.

When raised separately from their parents, for whatever reason, juveniles can be kept under the same terrarium setup and conditions as adults. Juveniles of the same age can be kept in groups until they reach sexual maturity. Thereafter, they may start fighting. I prefer to keep juveniles in pairs. If fighting starts as they grow, partners can be changed in an attempt to establish breeding pairs of unrelated individuals.

In my experience, a terrarium for raising a pair of juvenile gidgee skinks should measure no less than 40 x 70 x 50 centimeters.

In smaller terrariums, even with careful hygiene, the air tends to overheat and become stuffy, increasing the chances of illness.

Egernia stokesii stokesii can be bred at 3 or better 4 years of age. Breeding at a younger age is usually harmful for the female - birthing complications are common.

Diet 

Proper nutrition of reptiles is a very broad and important topic that cannot be covered thoroughly in this article. Unfortunately, the available literature on the subject contains many contradictions as well as fabulous recipes for mixing the perfect, convenient, all-in-one feed. The ease for the keeper is often given more importance than the nutritional needs of the animals. Most captive animals are not extremely badly fed, but very few are extremely well fed!

Diet largely determines the success or failure of keeping and breeding these lizards, and should be entirely designed for the particular needs of the species. The gidgee skink is an omnivorous lizard. Its digestive system is intermediate between that of an herbivorous lizard and that of a carnivorous lizard. The ability to eat both plant and animal foods allows the gidgee skink to eat whichever food it can find, and thereby survive in its natural habitat.

But what about in the terrarium? To answer this question, it is important to understand that the captive skink need not be given the exact same types of foods that it would find in its Australian habitat, but it does need to be given the same proportions of nutrients. The proper balance of proteins, carbohydrates, fats, vitamins, minerals, trace elements, and fiber is crucial for the health of the skink. Cat food is much too high in protein and can lead to kidney problems in reptiles.

As in herbivores, fiber is important for digestion in the omnivore - involved in maintaining a healthy intestinal flora for the natural breakdown of certain nutrients. Remember that coprophagy is also involved in maintaining intestinal flora. Parasite management is therefore important - a veterinary examination should be done at least twice a year for animals kept in terrariums, and more often for animals kept outdoors in summer (which is preferable). Treatment should be specific to the particular parasites found.

Fiber in the diet not only increases the bulk of feces, but also changes its structure, creating more surface area on which digestive microorganisms can work, and thereby increasing the ability of the animal to absorb nutrients from food ingested. Intestinal flora is kept in balance, and undigested fiber helps to clean out the digestive tract, further contributing to efficient nutrient absorption.

Every week I give the skinks a supplemental handful of fresh meadow hay chopped into 1-centimeter lengths and enriched with powdered calcium and vitamin supplement. The skinks immediately begin nibbling on leaves and stems. Caution is advised when giving supplements. Overdoses of fat-soluble vitamins (A, D, E, and K) can lead to severe health problems. Calcium should be given in the proper proportion to phosphorus. Too much calcium is just as bad as a calcium deficiency. A good way to supplement calcium in the diet, especially for gravid females, is to scatter crumbled eggshell on the floor of the terrarium. Occasionally an entire hard- cooked egg can be chopped up, shell and all, and mixed with greens.

Food should always be given at room temperature. Vegetables given straight out of the refrigerator are too cold, and can lead to digestive problems or even death.

In the wild these skinks have fresh green vegetation available for only a short period of the year. Most of the year they must make do eating dried plants. Many herbivorous or omnivorous terrarium animals are given a diet too high in fruits or vegetables (such as lettuce) that are high in water content and low in fiber. The water is quickly absorbed, and the remaining intestinal content has little volume with little surface area, resulting in inefficient digestion. These conditions tend to favor pathogens rather than “good” intestinal microorganisms, resulting in an overworked and thereby compromised immune system. The lizards initially show no external symptoms of their weakening condition, but they become increasingly vulnerable to illness. A diet high in fruit, specifically fruit sugar, raises the risk of yeast infections.

Leafy branches of fruit trees or shrubs can be placed in the skink terrarium. The animal will busy itself nibbling away every leaf. Be careful not to use toxic plants, either as food or planted in the terrarium.

 

 

These animals eat the leafy parts of the hay and use the rest for hiding. Putting a couple of mealworms in the hay will keep the lizards busy for a while

 

 

 

For the animal portion of the diet, the skinks can be offered the usual insect prey commonly given to captive reptiles. Giant mealworms (Zophobas) are especially good sources of protein for gravid females, but even in this case care should be taken not to overfeed these rich food items. If insect prey is raised at home and fed vitamin and mineral supplements, additional nutritional supplements should be given to the skinks only if absolutely necessary.

 

King mealworms (Zophobas morio) are a favorite food of the captive gidgee skink

 

Simply by providing a well-balanced diet for captive gidgee skinks, it is surprising how interesting the behavior of the animals can become.

Acknowledgments

Special thanks to Alexandra Hofer for taking care of the gidgee skinks during the weeks when I could not be at home.

Bibliography

COGGER. H. G. 2000. Reptiles & Amphibians of Australia. 6th edition. Reed New Holland.

GREER, A. E. 1989. The Biology & Evolution of Australian Lizards. Surrey Beatty & Sons Pty Limited, Chipping Norton NSW.

HAUSCHILD, A., and P. GASSNER. 1995. Skinke im Terrarium. Landbuch, Hannover.

MAIN, A. R., and C. M. BULL. 1996. Mother-offspring recognition in two Australian lizards, Tiliqua rugosa and Egernia stokesii. Anim. Behav. 52: 193-200.

MULLER. M. J. 1996. Handbuch ausgewahlter Klimastationen der Erde. Forschungsstelle Bodenerosion der Universitat Trier Mertesdorf (Ruwertal), Trier.

SCHILDGER, B. 2000. Die Anwendung bildgebender Verfahren zur Geschlechtsbestimmung bei Reptilien. Praktischer Tierarzt 81(2): 150-160.

STORR, G. M., L. A. SMITH, and R. E. JOHNSTONE. 1981. Lizards of Western Australia - I. Skinks. University of Western Australia Press with Western Australian Museum.

WILSON, S. K., and D. G. KNOWLES. 2000. Australia's Reptiles - A Photographic Reference to the Terrestrial Reptiles of Australia. Collins Publishers, Australia.

This article was published in the magazine "REPTILIA" No. 51 April 2007