NEST TEMPERATURE AND RESPIRATORY GASES DURING NATURAL INCUBATION IN THE BROAD-SHELLED RIVER TURTLE, CHELODINA-EXPANSA (TESTUDINATA, CHELIDAE)

Temperature was monitored in three natural nests, and oxygen and carbo n dioxide partial pressure monitored in one natural nest of the broad- shelled river turtle, Chelodina expansa, throughout incubation. Nest t emperature decreased after nest construction in autumn, remained low d uring winter and gradually increased in spring to a maximum in summer. In a nest where temperature was recorded every hour, temperature typi cally fluctuated through a 2 degrees C cycle on a daily basis througho ut the entire incubation period, and the nest always heated faster tha n it cooled. Oxygen and carbon dioxide partial pressures in this nest were similar to soil oxygen and carbon dioxide partial pressures for t he first 5 months of incubation, but nest respiratory gas tensions dev iated from the surrounding soil over the last three months of incubati on. Nest respiratory gas tensions were not greatly different from thos e in the atmosphere above the ground except after periods of rain. Aft er heavy rain during the last 3 months of incubation the nest became m oderately hypoxic (P-O2 similar to 100 Torr) and hypercapnic (P-CO2 si milar to 50 Torr) for several successive days. These short periods of hypoxia and hypercapnia were not lethal.