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I investigated habitat use, home ranges, activity patterns, thermal biology, and energetics of sympatric western diamondback (Crotalus atrox), black-tailed (C molossus), and tiger rattlesnakes (C. tigris) in the Sonoran desert of southeastern Arizona. The three species differed significantly in their choice of habitats, and habitats used by snakes were significantly influenced by season. Crotalus atrox used mainly creosotebush flats, but switched to rocky slopes during winter. Crotalus molossus frequented rocky areas, but during late summer and fall used arroyos and creosotebush flats. Crotalus tigris was a strict rock dweller during winter and spring, but used edges of arroyos during summer. Crotalus atrox, C. molossus, and C. tigris had mean home range sizes of 5.42 ha, 3.49 ha, and 3.48 ha, respectively. Over the year, snakes traveled a mean distance of 12.94 km (C. atrox), 14.99 km (C. molossus), and 9.29 km (C. tigris) during approximately 95 h of surface activity. During their active seasons, 1 March to 15 October, rattlesnakes traveled, on average, 50.8 m/d (e. atrox), 42.9 m/d (C. molossus), and 32.9 m/d (C. tigris). All three species had mean activity temperatures near 29.5 C. The three species showed no significant differences in home range, activity distances, or body temperatures. Rattlesnakes had standard metabolic rates similar to those of other Crotalus species, but only 40% those of other squamate reptiles of similar mass. They could fulfill yearly maintenance energy requirements with a prey quantity equivalent to 93% of their body mass; these energy demands could be met with 2 to 3 large meals.