Body temperatures of ectotherms critically affect their bioenergetics, and thus have consequences for multiple aspects of population ecology, including recruitment, survival, and population viability. We compared body temperatures and movement between gravid and non-gravid female Timber Rattlesnakes (Crotalus horridus) inhabiting northwestern Arkansas using radiotelemetry. Body temperatures (n = 839) were recorded from six gravid and five non-gravid adult female rattlesnakes using temperature-sensitive radiotelemetry. Mean T_bs were calculated for each hour of the day from 15 July–22 August 2002 and used to construct a representative 24-hour body temperature profile. Gravid females had significantly higher mean T_bs in the early morning and again for most hours in the late afternoon and first half of scotophase. Overall snake T_bs were higher during the day and lower at night. Moreover, gravid females exhibited lower variation in T_b during late afternoon than did non-gravid females. Mean area used (± SD) by gravid females (0.4 ± 0.4 ha) was significantly less than that of non-gravid females (2.4 ± 1.8 ha), and daily movement (18.2 ± 6.1 m/day) and overall distance traveled by non-gravid females (827.4 ± 234.4 m) was over twice that of gravid females (8.8 ± 4.6 m/day; 384.0 ± 236.1 m). Understanding the thermal ecology of reproduction in this viviparous capital breeder provides valuable information for habitat management and species conservation.