Investigatory behavior inthe plains garter snake (Thamnophis radix) and several additional species

Garter snakes (Thamnophis radix), hognose snakes (Heterodon platyrhinos), and rattlesnakes (Crotalus species) flick their tongues and crawl about in an open field containing no food or sexual (i.e., reproductive) odors. As Experiment I shows, the taxa differ reliably in both rate of tongue flicking and rate of locomotion. In Experiment II, garter snakes (Thamnophis radix) placed into an open field for 5 min showed more tongue flicking than snakes that were handled and placed directly back into their home cages, indicating that the first group was exploring the apparatus rather than responding only to handling. During Minutes 3 through 5 (Experiment III) in the open field, garter snakes emitted fewer tongue flicks than they did during the first minute, and after 20 min, the rate of tongue flicking was virtually zero. However, snakes were capable of responding to presentation of new objects and/or odors, indicating that the previous response decrement was not derived from effector fatigue but rather from some habituatory process. Experiment IV revealed that satiated snakes habituated more rapidly than hungry snakes during exploration ofihe open field. Hence, exploratory behavior in these snakes is at least partially under the control of the same factors which mediate food·related appetitive activities. Although researchers have long known about the involvement of the vomeronasal system (tongue and Jacobsen's organ) in snake and lizard investi­ gatory behavior (e.g:, Carr, 1934), there are few systematic studies directed specifically at this system. Moreover, the major papers have been primarily concerned with the manner in which the system func­ tions in locating potential mates (Noble, 1937) or food (Burghardt, 1966, 1967, 1969, 1970). Hence, the extent to which tongue flicking occurs during exploration of environments containing no food or ~exual odors is unclear; it is also uncertain if the chemoreceptive tissues of the tongue and! or Jacobsen's organ are sensitive to molecules other than those arising from prey and mates. A main pur­ pose of this investigation is to provide an answer to the first of.these two questions. At a more general level, the study by Glickman and Sroges (1966) provides additional inspiration for the present work. These investigators introduced novel objects (e.g., blocks of wood, pieces of plastic tube, lengths of chain, etc.) into the cages of various mammals and reptiles at the San Diego Zoo; and they recorded the number of visual orientations to these objects as well as the number of contacts each animal made with the objects (with mouth, nose, paws, etc.). Primates and carnivorous mammals had the highest mean scores for all objects, and