OBSERVATIONS ON THE FEMALE REPRODUCTIVE-CYCLE OF CAPTIVE GIANT TORTOISES (GEOCHELONE SPP.) USING ULTRASOUND SCANNING

The reproductive activities of one adult female Galapagos tortoise (Ge ochelone nigra) and three adult female Aldabra tortoises (Geochelone g igantea) were monitored over 2 yr using ultrasound scanning. A nonrest raining technique of tactile stimulation was used for all examinations . Developing, preovulatory, and atretic ovarian follicles, as well as eggs at various stages of shell deposition, were identified and measur ed. In G. nigra, follicles became preovulatory at a diameter of 40-42 mm and eggs were laid 34-84 days (mean = 55.6, n = 5) after the thin-s helled eggs were first detected in the oviducts. Geochelone nigra was capable of retaining eggs, with the shell already formed, until the ne xt breeding season. No eggs have been produced by G. gigantea during t heir stay in Zurich Zoo although follicles of 38-40 mm have been obser ved frequently in two animals.