Incubator With Electronically Regulated Daily Temperature Cycle: - Part II   Victor Loehr  Reprinted with permission of Victor Loehr.

Introduction

In Loehr (1996) several points were explained with respect to the incubation of eggs of tortoises at fluctuating temperatures in a daily temperature cycle. A model of an incubator with the possibility to realize such conditions was presented. A description of the incubator can be found in the article that is mentioned above. In the mean time, the incubator that was described has been tested by the author, by incubating eggs of Malacochersus tornieri and Homopus s. signatus in it.

New incubator

After having used the incubator that was described in Loehr (1996) for some time, a defect appeared. One night, the eggs cooled down to 20° C by a defect of the heating wire. This caused me to rebuild the incubator once again. Rather than one, now two heating wires (28 Watts each) were installed, in order to avoid too low temperatures during a possible defect of one of these in the future. One of the wires is located below at the front and the other in the top behind in the incubator.

During the time that the "refrigerator" had been used, it had become clear that the sight on the eggs through the small windows in the front door did not allow inspection of the eggs very well, when the number of eggs in the incubator was large. Because of this, furthermore a chipboard case of the same size was built with a front door of chipboard and a double glass layer top. Through the glass top in all cases the entire incubator can be inspected. For isolation purposes, the chipboard is covered with a layer of Styrofoam (5 cm) at the outside and with a layer of tin foil at the inside. For the rest, the composition of the incubator remained unchanged. After the heating wire of the first incubator had broken down, the eggs were transferred to the newly built incubator within several hours.

Material and methods

All eggs were incubated on a substrate of vermiculite mixed with water in a 1:3 (weight) ratio in open containers. The substrate was remoisted only prior to the expected hatching date. A total of six eggs of M. tornieri and five eggs of H. s. signatus was incubated at temperatures that fluctuated between 25° C (during the night, for twelve hours) and 32° C (during the day, for twelve hours). In figure 1 the fluctuation of the temperature is shown graphically.

Results and conclusions

In table I, the results of the incubation of eggs of M. tornieri and H. s. signatus in the incubator with daily temperature cycle are presented. In eggs of both species, a high hatching rate was accomplished (M. tornieri: 100%, H. s. signatus: 80%).

Several reasons disable drawing conclusions from the results that are presented here, with respect to the effect of incubation of eggs of the two species that were tested at fluctuating temperatures. The eggs were cooled down to 20° C once during incubation and the total number of observations is too small. Furthermore, no suitable results for comparison are available. Nevertheless, the hatching rate of the eggs of M. tornieri of 100% is far higher that has been observed in eggs of other keepers of this species (Wilke, 1983 (68% (n=22)); Darlington and Davis, 1990 (22% (n=109)); Pauler, 1990 (40% (n=5); M. Schmalz, pers. med.). Although I am not familiar with the exact incubation methods used by these persons, presumably incubation at fluctuating temperatures was not practised. Personally, when incubating eggs of M. tornieri at constant temperatures (but at the same time heating the incubator by means of light bulbs rather than heating wires) and remaining similar conditions, I have obtained a hatching rate of only 40% (n=5). Firm conclusions on the rate to which the fluctuating temperatures are the cause of the high hatching rate in eggs of M. tornieri only can be drawn when sufficiently large numbers of eggs have been incubated in equal numbers in two incubators. The conditions in both incubators should be similar, except for the temperature regime.

Nevertheless, I would like to conclude that the positive first breeding results certainly make it reasonable to continue conducting experiments incubating tortoise eggs at fluctuating temperatures.

Different electronics

The regulation of the temperature in the incubator that was described in Loehr (1996) was secured by a homemade temperature control unit, existing of two electronic thermostats and a rebuilt time control unit. Some time ago, I found a unit that is suitable for instant establishing a daily temperature cycle in incubators. If you wish to receive more information on this apparatus, the author can be contacted.

New Results

This year I have used the incubator with diurnal temperature cycle for the second year to incubate eggs of Malacochersus tornieri and again I found a 100% hatchling rate (n=5)!

Literature

Darlington, A.F. and Davis, R.B. (1990). Reproduction in the pancake tortoise, Malacochersus tornieri, in captive collections. Herp Review 21(1): 16-18.

Loehr, V. (1996). Een model voor een broedstoof met elektronisch geregelde, dagelijkse temperatuurcyclus. De Schildpad22(5): 38-42.

Pauler, I. (1990); Zur Nachzucht der Spaltenschildkröte Malacochersus tornieri (Siebenrock, 1903). Herpetofauna 12(66): 6-10.

Wilke, H., 1983; Breeding the pancake tortoise Malacochersus tornieri at Frankfurt Zoo. International Zoo Yearbook 23:; 137-139.