Deposition and Incubation
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
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.
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.
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)
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
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.
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