Thermal preferences of hatchling new Guinea crocodiles: Effects of feeding and ontogeny

1. 1. The body temperatures (Tbs) and thermal behavior of hatchling New Guinea crocodiles (Crocodylus novaeguineae) were monitored in a terrestrial-aquatic thermal gradient exposed to the natural photoperiod. 2. 2. At 0–2 weeks of age, hatchlings selected Tbs of 33.4–33.9°C that were significantly elevated by 1.4–2.9°C above levels preferred subsequently. Higher Tbs were pronounced during the period of yolk absorption and may have facilitated the rapid assimilation of unabsorbed yolk immediately after hatching. A similar thermophilic response has been noted for hatchlings of two other species of crocodilians. 3. 3. At 2–5 weeks of age, hatchlings selected lower Tbs (31.8–32.2°C) relative to previous values. Tbs were not elevated or less variable in response to feeding and an increase in heat-seeking behavior was not apparent. 4. 4. Hatchings (2–5-weeks old) preferred Tbs that were approx 2°C higher than the Tbs maintained by a juvenile and adults monitored in a natural setting. Thermal preference in New Guinea crocodiles appeared to decline to adult levels within the first two years of life. 5. 5. Ontogenetic changes in thermal preference, particularly thermophily during early life, are evident in this crocodilian species and may occur in other reptiles as well.