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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. [ABSTRACT FROM AUTHOR]

Abstract Ontogenetic shifts in habitat use are widespread, especially in ectothermic taxa in which juveniles may be an order of magnitude smaller than large adult conspecifics. The factors that generate such habitat shifts are generally obscure, but we studied an unusual system that allowed us to compare consequences of habitat selection between adults and juveniles. Pit-vipers (Gloydius shedaoensis ) on a small island in north-eastern China feed almost entirely on seasonally migrating birds. During the spring bird-migration period, individual snakes consistently re-used either arboreal or terrestrial ambush sites. Snakes in trees were smaller (and more philopatric) than snakes on the ground. This ontogenetic shift in habitat use may reflect the difficulty of capturing birds on the ground, especially by small snakes. In laboratory trials, large (adult) pit-vipers struck faster, further and more accurately than did small (juvenile) snakes. In experiments with free-ranging snakes, the proportion of strikes hitting the bird was lower for juveniles than for adults, and lower for terrestrial snakes than for arboreal snakes. Additionally, adult snakes generally seized the bird by the head whereas juveniles frequently struck the body or wings (and thus, obtained a less secure grip). Arboreal ambush sites may facilitate prey capture not only because they give access to smaller birds but also because they render the bird's location more predictable and, hence, enable the snake to position itself optimally prior to the prey's arrival. Because juvenile pit-vipers are less capable strikers, and are small relative to available prey items, they may benefit from the greater ease of prey capture from branches. Thus, the ontogenetic shift in habitat selection within this species may be because of ontogenetic shifts in the vipers’ ability to capture and ingest large, mobile prey. [ABSTRACT FROM AUTHOR]