The breeding of Pseudemydura umbrina
Female P. umbrina produce only one clutch of three to five hard-shelled eggs per year. Laying occurs in November or early December before the aestivation period begins. Egg size is approximately 35mm x 20mm (Burbidge 1981). The average incubation period is 180 days and hatching, triggered by a drop in incubation temperatures, occures in the beginning of the following winter. (Burbidge and Kuchling, 1994)
Sex of P. umbrina hatchlings is determined genetically (Thompson 1988, Palmer-Allen and Beynon 1990). This has been confirmed by Dr Kuchling who came to the same conclusion after undertaking histological examination of several hatchlings.
Growth is slow and varies considerably from year to year and between animals depending on seasonal conditions - the lower the annual rainfall the shorter the swamp life and the slower the growth rate. This means that age to sexual maturity also varies between animals and can be up to 15 years or more. At Twin Swamps Nature Reserve the average age to sexual maturity is 11 years (Burbidge and Kuchling, 1994). Sexual maturity in females occurs at 112mm carapace lenght (Kuchling & Bradshaw, 1993).
At Perth Zoo captive breeding was attempted in a low key, non-interventionist way from 1964, when Western Swamp Tortoises were first kept, until 1979 (Spence et al. 1979). Success was, however, very low with only four animals still being alive from the 26 that hatched between 1966 and 1977. In 1979, the three remaining adult females from the Zoo population were transferred to the Western Australian Wildlife Research Centre for more intensive husbandry and the use of interventionist techniques in obtaining and incubating eggs. During the first year three eggs were obtained by oxytocin inducement and incubated artificially. Two hatchlings were obtained, but one died in its first year and the other in its second. In 1980, 14 eggs were produced and artificially incubated; six of these hatched, but the hatchlings did not survive for more than a few months. This work did, however, show that eggs could still be produced by the captives and demonstrated that the hatching of P. umbrina eggs is triggered by a drop in incubation temperatures; if the incubation temperature is maintained most embryos develop to hatchling size but do not hatch and eventually die. This adaptation presumably prevents hatchlings emerging before winter. No further eggs were produced by the captive animals until 1987.
In 1987 Dr G. Kuchling arrived at The University of Western Australia from Austria to work with Professor S.D. Bradshaw on the hormonal control of reproduction in the Oblong Tortoise Chelodina oblonga. Later he asked the Department of Conservation and Land Management if he could help with 11 captive breeding in P. umbrina, a suggestion that was welcomed. The development of techniques for the examination of the female reproductive tract using ultra-sound scanners (in collaboration with Dr Bruno Colomb) was a breakthrough, enabling measurements to be made of egg follicle development for the first time (Kuchling 1989). Previously it was not known whether eggs were being developed until ovulation had taken place and the shell had been laid down. Even then, palpation in Western Swamp Tortoises is difficult because of the small leg openings between the carapace and plastron, and the only certain method of counting eggs was via the use of radiography. In 1987 seven eggs were obtained from two captive females. These eggs were incubated artificially, but none hatched, the embryos dying at an early stage of development. The reasons for this are not clear: recent research suggests that the most likely explanation is poor quality eggs due to inadequate nutrition of the females that produced them.
Also in 1987 the Department of Conservation and Land Management and the Zoology Department of The University of Western Australia developed a budget for a two and a half year captive breeding project and sought and obtained funds from the World Wide Fund for Nature Australia, the Australian National Parks and Wildlife Service, the Western Australian Nature Conservation and National Parks Trust Account and the Western Australian Department of Conservation and Land Management. The project was carried out by Dr Kuchling, now a Research Fellow at Zoology Department, The University of Western Australia, utilising tortoises kept at Perth Zoo and at the Department of Conservation and Land Management's Wildlife Research Centre. Perth Zoo and the Department of Conservation and Land Management have supported the project with staff and with additional funds and The University of Western Australia has provided facilities and financial administration. Perth Zoo has obtained external sponsorship for the construction of new facilities for the captive tortoises and hatchlings, husbandry was greatly improved (Kuchling and DeJose 1989) and the captive colony was increased by addition of tortoises captured outside Ellen Brook and Twin Swamps Nature Reserves. The project was supervised and coordinated by the Western Swamp Tortoise Captive Breeding Project Management Committee of Dr Andrew Burbidge (Conservation and Land Management, chair), Mr John DeJose and Mr Darryl Miller (Perth Zoo) and Professor Don Bradshaw and Dr Gerald Kuchling (Zoology Department, The University of Western Australia). This project has been successful and the results are shown in Table 2. The captive breeding project team was a finalist for the 1990 IBM Australia Conservation Award. In mid-1991 responsibility for the project was transferred to Perth Zoo, with Dr Kuchling continuing to provide advice and help.
Table 2. Results of captive breeding project, 1987-1992 (Source: Burbidge and Kuchling, 1994)
Period |
Number Laying |
Viable Eggs Laid |
Number Hatched |
Number Alive May 1992 |
1987/88 |
2 |
7 |
0 |
- |
1988/89 |
3 |
12 |
11 |
5 |
1989/90 |
5 |
13 |
11 |
11 |
1990/91 |
6 |
18 |
16 |
16 |
| 1991/92 |
6 |
15 |
12 |
12 |
Major Reference:
Burbidge, A. and Kuchling, G. (1994) WESTERN SWAMP TORTOISE RECOVERY PLAN
for the Western Swamp Tortoise Recovery Team