AN ECOLOGICAL STUDY OF OXYGEN-CONSUMPTION IN THE MOTTLED ROCK RATTLESNAKE, CROTALUS-LEPIDUS-LEPIDUS, AND THE BLACK-TAILED RATTLESNAKE, CROTALUS-MOLOSSUS-MOLOSSUS, FROM 2 POPULATIONS

Studies of metabolism are critical to calculating ecological energy balance. Metabolism of rattlesnakes as a group has been little studied. I investigated the effects of mass, temperature, sex, time of day, population of origin, and species on O2 consumption of field-acclimatized Crotalus lepidus lepidus and Crotalus molossus molossus from two populations in Big Bend National Park. Factors that significantly affected O2 consumption included mass, temperature, sex, time of day, and population of origin. No mass-independent differences between these species were identified. Populations significantly differed in the relationship between body mass and metabolic rate. Oxygen consumption increased with increasing temperature and was lowest between 0700 and 1300 hours CDT. Non-gravid females bad lower rates of O2 consumption at 25-degrees-C than did gravid females and males. This is consistent with results of some previous studies. Mass-specific metabolic rates of C. l. lepidus and C. m. molossus were lower than those of other snakes studied to date. Regression models for the prediction of maintenance cost as a function of body mass and temperature are reported.