J. Zool., Lond. (A) (1986) 208, 541-558

A. HAILEY AND P. M. C. DAVIES

(With 9 figures in the text)

The activity metabolism (aerobic and anaerobic), performance (burst speed and endurance) and defence behaviour (static or active) of the snake Natrix maura were investigated in relation to size, sex, temperature and fasting. Conditions which reduced performance (low temperature, fasting) promoted the use of static defensive behaviour. Aerobic scope for activity decreased with increasing size, but this was compensated for by increased capacity for anaerobic metabolism. Burst speed (as lengths time ^-1) was slightly lower in large snakes; endurance was much lower in small snakes. Increased use of static defence by small snakes is related to their predators, which are likely to take occasional snakes in a diet of worms; a balled, still snake may not provide a stimulus for feeding. Large snakes have predators which feed on vertebrates and may recognize them as food in any position, and so they are better off trying to escape.

Aerobic scope was not maximal at the mean selected body temperature (25^oC), but increased right up to near lethal temperatures (> 35^oC). Anaerobic metabolism (lactate production) was less temperature-sensitive, and accounted for about 80 and 50% of the energy produced during 30 s and 5 min of maximal activity, respectively. Resting and active oxygen consumption were weight-dependent, VO₂ µ W^0.75, the same exponent as that of interspecific comparisons. This exponent was independent of temperature and acclimation state. Acclimation to a variable or constant temperature regime had no effect on maximal oxygen consumption, but there was a significant effect on resting metabolic rate, possibly attributable to energy conservation when inactive. There were no differences in activity metabolism, performance or defence behaviour between similar-sized snakes of different sexes.