Thermal influences on foraging ability: body size, posture and cooling rate of an ambush predator, the python Morelia spilota

1. The interface between thermal biology and foraging mode has attracted little scientific attention, but may be crucially important to the biology of ectothermic predators. Slip & Shine (1988c) suggested that the ability of large heavy-bodied snakes to ambush nocturnally active mammals relied on the snakes' control of cooling rates through their thermal inertia (via body size and postural adjustments) and microhabitat selection.
2. We tested assumptions underlying this hypothesis, using Diamond Pythons ( Morelia s . spilota ) from southeastern New South Wales. Our laboratory studies confirmed that larger body sizes and coiled postures significantly retarded cooling rates, and that body temperature affected the snakes' ability to detect potential prey items.
3. The magnitude of these effects on cooling rates was great enough to extend the time period substantially over which an adult Diamond Python, lying in ambush in a suitable microhabitat, would be able to detect and capture nocturnally active prey. For example, the times taken for pythons to reach thermal equilibration under our experimental conditions (cooling from 33 to 12°C) were <1h for hatchling pythons regardless of posture, 1 h for outstretched juveniles, 2 h for coiled juveniles and outstretched adults, and almost 8 h for coiled adults.
4. The high rates of cooling of juvenile pythons, even when they are tightly coiled, may force them to rely upon diurnally active prey rather than crepuscular or nocturnal species.