We studied the spatial and reproductive ecology of a population of Copperheads (Agkistrodon contortrix), a North American pitviper, in a basalt trap-rock ecosystem in the central Connecticut River Valley, a region that constitutes the northeastern extreme of this species' geographic range. Adult males (n  =  20) and females (n  =  15) were surgically implanted with radio-transmitters and tracked every 48 h during the active season (April through October) for three consecutive years (2001 to 2003). From late autumn to early spring (November through March), when snakes were hibernating and thus inactive, tracking was reduced to once per week. We generated data on movement and other spatial parameters for each subject using GPS coordinates. There were significant sex differences in activity range size and multiple movement parameters. Throughout the active season males had greater activity range sizes and showed greater movement than females. This trend was pronounced during the mating season, which was restricted to late summer and early fall (late July through September). In contrast to most populations of A. contortrix from more southern and western localities, we did not observe any sexual activity (e.g., courtship, coitus, and male–male fighting) in the spring. Individuals of both sexes showed annual fidelity to: (i) activity range location, (ii) activity range size, (iii) movement distances, (iv) particular features of their activity ranges (e.g., refuge sites), and (v) hibernation sites. Males and females showed no difference in preferred seasonal habitats. In both sexes, shifts in habitat associations during the active season included migrations from over-wintering sites within basalt trap rockslides to upper-elevation, open deciduous forest during the summer foraging and reproductive season. Parturition in the field was recorded in eight instances and was always close to one of the two hibernacula used by the individuals in the study area.