Because of their low metabolic costs, ectothermic predators can specialise on prey resources that are available for only a brief period each year. Endemic pit-vipers (Gloydius shedaoensis) on a small island in north-eastern China offer an extreme example of this phenomenon, with adult snakes feeding only on seasonally migrating birds that are available for a few weeks in spring and autumn. We surgically implanted radiotransmitters in 16 pit-vipers, and located the snakes at weekly intervals for the next 12 months to record activity, movements, home ranges, habitat use, body temperatures and associated environmental temperatures. The snakes were extremely sedentary, with daily displacements averaging < 2 m and home ranges < 0.3 ha. The snakes maintained diurnal body temperatures around 25°C throughout the active season. Diurnal activity was reduced in summer, when birds were unavailable. Males and females were similar in most aspects of their ecology, except that females were often found in trees in autumn (feeding) while males were more often on the ground at this time (probably mate-searching). Males also tended to shelter under vegetation rather than under rocks. The low vagility, relatively low body temperatures and summer inactivity of these snakes may reduce energy expenditure, and thus facilitate survival in a habitat where food is available only in brief periods several months apart.