Egg Deposition and Incubation

If proper environmental conditions are met, female varanids will go through a regular reproductive cycle in captivity. In compatible groupings, males will usually only try to copulate with females for a period of two to three days when females are receptive. If breeding is successful, egg deposition usually occurs within two to three weeks of copulation. In the week prior to egg deposition, females can be observed basking for prolonged periods of time. Feeding generally slows down during this period and females may appear restless. Females may also show some physical signs of being gravid that can be observed by the discerning keeper. Gravid females may show distension in their abdominal region and the area around the base of their tail may show varying degrees of fat loss. Females that display these characteristics are generally ready for egg deposition.

Once females are at the end of their gestation period, they will search the enclosure looking for a suitable nesting site. If substrate conditions have been maintained as outlined in the “Captive Environment” section, females should have little difficulty locating such an area. Some keepers have suggested that females will only breed if they have already chosen a proper nesting site. If females are unable to find one, it is unlikely that they will deposit eggs successfully. Other keepers have suggested that females will generally start looking for a nest at the end of their gestation period. Either way, if proper environmental conditions and nutritional requirements are met, a female will likely reproduce and deposit her eggs successfully. Many keepers like the idea of using a nest box because it cuts down on the amount of substrate required within the enclosure and it makes it easier to find eggs once they have been laid. Nest boxes are not recommended because they rarely lead to continual breeding success. Because of their small volume, nest boxes are very susceptible to environmental fluctuations. They tend to dry out quickly, overheat, or get to cold. Unless nest boxes are monitored very closely, they are generally not a good option for gravid female monitors. Enclosures filled with a deep substrate provide females with more options and more room to burrow. The greater the volume of the substrate, the more static its temperature and moisture content will be. This greatly increases the likelihood that a female will be able to find a suitable nesting site and deposit her eggs in a timely fashion. Females which are unable to find a proper nesting location will often retain their eggs. If appropriate measures are not taken by the keeper to correct this problem, eggs may be retained past the “critical point”.
Beyond this point, several things can occur. One possibility is that a female may die due to exhaustion and egg retention. Some females will retain their eggs for so long, and expend so much energy trying to locate a suitable nest, that exhaustion and stress lead to their death. A second possibility is that a female will abandon her search for a proper nest and lay her eggs throughout the enclosure or in an unsuitable location. If this occurs, the viability of the eggs has been greatly reduced due to extended retention and very few if any will ever hatch. Females which have been exposed to the intense stress of a failed nesting attempt will often have difficulty with future nesting and generally display compromised reproductive ability. It is important to note that females in their first egg laying attempts are typically less selective about their nesting location than more experienced females. Therefore, fewer failed nesting attempts have been observed with younger females. Older, more experienced females are extremely selective about where they will deposit their eggs. If suitable conditions are not met, seasoned females tend to retain their eggs much longer and sometimes not lay them at all leading to their death.

Proper egg deposition does not take long to occur. Within the subgenus Odatria, the entire nesting event (site selection, burrow excavation & egg deposition) may take as little as six hours (as observed with several of the smaller species), but more commonly occurs over a period of approximately twenty four hours. Successful egg deposition is not a stressful experience for a healthy varanid. Females which have deposited their eggs successfully will appear thin, but alert, and will resume back to normal social and feeding behaviour immediately. Some females have been known to display nest guarding behaviour, where they are territorial of their nesting area for a period of time after their eggs have been laid. Once the keeper is certain that eggs have been laid, they should be removed from the enclosure and placed in an incubator. Excavating the eggs is a delicate procedure. Start by locating the entrance of the burrow. The substrate should be loosely packed where the female has been digging. Follow the loosely packed substrate through the length of the burrow. Borrows may extend from 15cm – 40cm from their entrance depending on the species and substrate depth. Avoid using hard objects (such as a spoon) to excavate the burrow. They increase the risk of damaging the eggs if contact is made. At the end of the burrow, the eggs will be deposited in a chamber. Gently remove the eggs from the chamber and place them in the desired incubation medium. Avoid rotating the eggs during this process. This is not critical within the first 24 – 48 hours after deposition as implantation is unlikely to have occurred. Eggs can be rotated during this period without consequence, but it is better to avoid doing so if possible. Once the eggs have been removed from the nesting site it important to fill it back in with substrate. If the nest is left uncovered females will shows signs of elevated stress due to the disturbance. It is important to note that males may need to be removed from an enclosure during egg deposition. Curios males may impede egg deposition and on rare occasions, even consume some of the eggs. Very rarely is this ever observed.

Egg Incubation
As experienced by many monitor enthusiasts, successful incubation of varanid eggs is no easy task. Monitor eggs have a relatively long incubation period (3-4 months in odatria), and in that time many environmental influences can affect the survival of the eggs. There is no concrete set of incubation guidelines that will work in every situation. When all variables are considered, the discerning keeper will have to develop their own recipe for their given situation.

To ensure that our varanid eggs have the best chance of successfully hatching, several guidelines and practices are followed and implemented here at Canadian Coldblood. When considering these techniques, be aware that some adjustments and considerations may have to be made for your given situation.

Environmental Considerations
Below are a few things to consider when setting up your varanid eggs for incubation.
1. Temperature (inside and outside of your incubator)
2. Incubator Dimensions
3. Incubation Medium
4. Incubation Medium : Water (Ratio)
5. Ventilation

1. Temperature
Incubation temperatures are not as critical as one might think. Varanid eggs can be incubated successfully through a fairly wide range of temperatures (80°F - 88°F or 26.7°C – 31.1°C). Healthy hatchlings have emerged throughout this temperature range with eggs incubated at the colder end of the spectrum taking noticeably longer to hatch. Ideally, eggs should be incubated in the range of 85°F - 86°F (29.4°C - 30°C). Periodic temperature fluctuations of 1°F - 2°F are regularly observed and do not appear to harm the eggs in any way. In fact, this sort of temperature fluctuation may be beneficial to the developing embryo as it mimics a more naturalistic incubation setting. Odatria eggs will typically hatch within 3 – 4 months at the aforementioned temperature range. It is important to note that standard incubators used by many hobbyists have only the ability heat their internal environment. If the incubator is placed in a room that gets hotter than the suggested suitable temperature range, the internal temperature of the incubator may reach dangerously high levels. This may lead to deformed offspring or the death of the embryos within the eggs.

2. Incubator Dimensions
Incubators of all sizes can be used to successfully incubate monitor eggs. But, as a general rule of thumb, the larger the internal dimensions of the incubator the more static its internal environment will be. This will provided a greater safety net incase of power outages or external temperature fluctuations. Larger incubators have a greater internal volume which will not respond as quickly to external influences. A small incubator is much more susceptible to external temperature and humidity fluctuations which can cause sharp peaks and valleys within the internal environment. Eggs exposed to repeated environmental irregularities of this nature rarely do well.

3. Incubation Medium
Monitor eggs can be successfully incubated on a variety of substrates. The two most commonly used products are Vermiculite and Perlite. Of these two products, Perlite appears to yield the results. Perlite is more porous which allows for better air penetration between the granules. This helps prevent excess mould and fungal growth. It also helps keep eggs from direct contact with any accumulated water that might be present. Perlite can also be dried easily and reused duiring future incubation efforts.

4. Incubation Medium : Water (Ratio)
When setting up your eggs for incubation it will be necessary to mix the incubation medium with water. A good starting point for the mixture is to mix 1 part water to 1 part medium by weight (ex. 100g of water : 100g of Perlite). It may be necessary to alter this ratio slightly given your situation.

5. Ventilation
It is important that the incubator and egg boxes within the incubator have good ventilation. This will ensure that fresh oxygenated air will reach the eggs. It will also inhibit the growth of mould and fungus within the incubation medium. It may be difficult to achieve good air flow while trying to maintain heat and humidity, but it is important to try and find this balance