In the not very distant past, reptiles were animals to be kept and appreciated for their forms, colors and actions, but few were bred in captivity. As a matter of fact, we didn’t even know how to determine the sex of many species. This is no longer the case. Today we now know how to sex many (if not most) species of reptiles, and because of successful breeding programs, species once considered rare are now seen with regularity. Here are a few points pertinent to the sexing and breeding of reptiles, although this is merely a guide based on one successful breeding program, and there are probably many additional ways of attaining similar successes.
Inducing Your Reptiles to Breed
Temperate reptiles often breed as they gather at their hibernacula in the autumn or as they become active in spring. Photoperiod (the seasonally changing hours of daylight versus darkness) plays an important part in inducing (cycling) reptiles to breed. Lowered barometric pressure (during the passing of frontal systems) also stimulates the breeding urge. Reptiles that dwell in the tropics where there is little seasonal variation in either photoperiod or temperature are stimulated to breed by seasonal variations in humidity and rainfall (the transition from the dry season to wet season).
At the advent of their respective breeding seasons, snakes and lizards usually undergo a post-hibernation or precopulatory skin shed. At this time, pheromones (olfactory stimulants that indicate reproductive readiness) are produced by the females. In some species, such as garter snakes and rattlesnakes that hibernate communally, breeding aggregations stimulated by pheromones occur. In others, such as the wide ranging indigo snakes or iguanas, the pheromones allow males to track females and breeding occurs during encounters.
It is often necessary to cycle captive reptiles reproductively by simulating naturally occurring conditions. One way is to follow the natural photoperiod when illuminating cages, for example by placing cages near a window. Another way is to provide an opportunity for temperate species to hibernate during the winter months. In the northern hemisphere this is December, January and February.
To hibernate reptiles, we convert a refrigerator (with a temperature of 48 to 52 degrees Fahrenheit) into a hibernaculum. Elevating cage humidity and a periodic gentle spraying with a fine mist can help cycle tropical species. There is some indication that at sexual maturity captive bred and born/hatched reptiles require less precise structuring to cycle reproductively than wild-collected specimens.
Determining a proper incubation temperature is important. In most cases a temperature of from 80 to 87 F will suffice. Some species incubate most reliably at the lower end of this, some at the higher. Sex of the hatchlings of some reptiles is determined by incubation temperature. Proper nest moisture is also important to successful incubation. Reptile eggs absorb moisture from the incubating medium. The medium should be just on the moist side of dry. Either under- or over- hydration will result in embryo death.
Temperature Dependent Sex Determination (TDSD)
It has been learned that the sex of some reptiles (crocodilians and some lizards and turtles) is determined early in incubation by the temperature within the nest (or incubator). Whether a baby will be male or female depends on nest temperature during the first two weeks of incubation. Babies of both sexes are produced by varying temperatures within the nest (the temperature is usually cooler on the bottom than on the top). As if sensing this, the females of most species carefully choose the placement of their nests. At latitudes where temperatures are ideal, a few female reptiles are egg-scatterers, preparing only a minimal nest, if any.
Temperature dependent sex determination (TDSD) works differently for different species. For example, male leopard geckos are produced at moderate nest temperatures (88 to 90 F) but females are produced at low nest temperatures (79 to 82 F) and again at very high nest temperatures (above 90 F). However, there is a greater egg mortality at the high end of the temperature spectrum and the females tend to be very aggressive at maturity. A nest temperature of 84 to 87 F will produce both sexes. Turtles seem to be the opposite, with males being produced at low nest temperatures and females at high. Determining and maintaining a proper incubation temperature is very important.
Besides resulting in abnormally high embryonic death, adverse incubation/gestation temperatures-sometimes by only a degree or two-are very apt to result in skeletal and shell deformities in embryos that do survive. Again, for most species, a nest or gestation temperature of 80 to 87 F will produce healthy babies.