Exotics – Reptiles ______

CHELONIAN EGG INCUBATION are commercially available, or may be built with readily available materials. The specific design of the incubator Charles Innis, VMD generally depends on the desired humidity range for New England Aquarium incubation. Boston, MA As a rule of thumb, eggs that have flexible shells require higher humidity than eggs that have rigid shells. Chelonian egg shells vary from flexible and leathery, However, the microclimate of the species should also be to hard and brittle. The thinnest parchment shelled eggs considered. For example, tortoises from humid forest are the most susceptible to changes in the hydric environments generally produce rigid shelled eggs, but environment. Clutch size, egg size, and nesting still require high humidity. In general, flexible shelled frequency vary among species. Pancake tortoises eggs should be incubated in a high humidity (Malacochersus tornieri), bowsprit tortoises (Chersina environment (80–100%). Rigid shelled eggs, depending angulata), Spider tortoises (Pyxis arachnoides), black- on the species may require high, low, or moderate breasted leaf turtles (Geoemyda spengleri), Sulawesi humidity. The reader is advised to consult the species forest turtles (Leucocephalon yuwonoi), and Central specific literature for details. American wood turtles (Rhinoclemmys spp.) generally A simple high humidity incubator can be made using produce only one (rarely two) very large egg(s) per two plastic containers (one larger than the other), a clutch, but may nest several times per year. At the other submersible aquarium heater, water, a brick, and a extreme, the large sea turtles, snapping turtles (Chelydra thermometer. The brick is placed in the larger container, serpentina and Macroclemys temmincki), and softshell and water is added to the height of the brick. The smaller turtles (Trionyx, Apalone, and others) may lay dozens of container is placed on top of the brick, and is filled with eggs per clutch, with some sea turtles nesting several incubation substrate and eggs. The thermometer times per year. measures the temperature of the egg box. The heater Nesting is similar among most species, with the thermostat is set at the desired temperature and fully female excavating a terrestrial, flask-shaped nest with submerged in the water. The egg box and outer her hind feet, depositing her eggs, covering the nest, container are both covered with lids with several and departing without further maternal care. An ventilation holes. The heated water will create a humid, exception to this general rule is the Burmese mountain warm environment. tortoise (Manouria emys ssp.) that constructs a nest by For incubation under dry conditions, commercial gathering sticks, dirt, and leaf litter into a pile, and then incubators may be used, or thermostatically controlled guards the nest for several days to weeks after heat pads may be used to construct an incubator. oviposition. Female western swamp turtles, A variety of incubation substrates have been used Pseudemydura umbrina, dig their nest with their successfully, including vermiculite, peat moss, gravel, forelimbs. The northern long-necked turtle, Chelodina soil, sand, etc. Some substrates do not retain moisture rugosa, may nest under water at sites that surface as the well and should only be used for low humidity incubation. dry season progresses. Chelonian eggs typically do not Vermiculite is most widely used. Water is added to the survive submersion for extended periods, but, it is vermiculite depending on the desired level of substrate thought the rugosa eggs lie dormant until the water water content. In general, a ratio of 1:1 water: vermiculite evaporates then development begins. by weight is successful. If the substrate dries In most turtle species, the gender of the embryo is significantly during incubation, additional water may be determined by the incubation temperature of the egg added. Some keepers periodically spray the substrate (temperature-dependent sex determination, TSD). In with water. If desired, the entire egg box can be some species, higher temperatures produce males, precisely weighed and water added as needed to while the reverse is true for other species. Most natural maintain a constant weight. The eggs are generally nests experience a range of temperatures, resulting in partially buried in the substrate to allow visual monitoring both male and female hatchlings. Some species show of the eggs during incubation. Reptile eggs should not genetic sex determination rather than TSD. be rotated after the first few days of incubation, as the After oviposition, eggs may be removed from the nest embryonic orientation may be disrupted. for artificial incubation. Several recent texts provide Many chelonian eggs have a slightly yellow to orange species-specific environmental requirements for hue when first oviposited. In many cases, fertile eggs will incubation of chelonian eggs. In addition, these texts “chalk,” or develop a flat white color over the first few provide critical temperatures for TSD for each species, if days of incubation. This change is due to the initial known. It is difficult to generalize about egg incubation of development of extraembryonic membranes. In some the nearly 300 species of turtles, but several rules of species, this is first noted as a small circular white spot thumb are provided herein. on the dorsal surface of the egg, which expands over For most species, incubation temperatures in the several days to encompass the majority of the egg. In range of 82–86°F are appropriate. Some tortoise species other species, this spot develops into a distinct white may require higher temperatures, while some forest leaf- transverse band across the short axis of the egg. litter species may require lower temperatures. Within several weeks, most eggs will show blood Temperature is maintained by locating the eggs in a vessel development. Candling can be accomplished in a thermostatically controlled room or incubator. Incubators variety of ways, but an ophthalmoscope with 1791 NAVC Conference 2008 ______transilluminator works well. One European institution has emerge from the egg. During this time, the yolk sac reported successful chelonian egg monitoring using an remnant is generally resorbed. Disturbing the hatchling avian egg cardiac monitor. at this time may traumatize the yolk sac. Once emerged Incubation length is highly variable among species. from the egg, the hatchling should be moved to a Most species require 2 to 4 months. In some species, it nursery enclosure appropriate for the species. Damp appears that the embryo may enter a diapause period paper towels provide an excellent substrate for the first that must be broken via environmental manipulation. For few days of life. Aquatic species are generally able to example, the spider tortoise (Pyxis arachnoides) from swim as soon as emerged from the egg. Madagascar seems to require an initial 3-month incubation, followed by a cooling period for 1 month, REFERENCES followed by 3 more months of higher temperature 1. Gurley R. Keeping and Breeding Freshwater Turtles. incubation. Failure to cool the egg seems to result in an Ada, OK: Living Art Publishing, 2003. indefinite delay in embryonic development. 2. Highfield A. Practical Encyclopedia of Keeping and Upon initial hatching, or pipping, the egg should be Breeding Tortoises and Freshwater Turtles. monitored closely. Turtles may take 1 to 2 days to London: Carapace Press, 1995.

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