ORIENTATION ABILITIES AND MECHANISMS IN NONMIGRATORY POPULATIONS OF GARTER SNAKES (THAMNOPHIS-SIRTALIS AND T-ORDINOIDES)

I tested the navigational abilities in nonmigratory populations of gar ter snakes (Thamnophis sirtalis and T. ordinoides) from Spectacle Lake Provincial Park on Vancouver Island, British Columbia. Canada. Displa cement studies were carried out from 1986-88 to determine the level of orientational abilities present in each species and to examine potent ial orientation cues. Snakes were displaced from their home range and tested in an arena under a variety of conditions. The results demonstr ated that nonmigratory T. sirtalis possessed advanced navigational abi lities. Advanced abilities may be absent in T. ordinoides. Thamnophis sirtalis demonstrated time-compensated solar orientation as determined by 6-h phase-delayed tests. Pheromone trails produced by gravid femal es, but not by males, may also provide an orientation guide for T. sir talis under some conditions. Thamnophis ordinoides did not respond in a discernible way to either solar or pheromonal cues. The findings of this study were compared with similar tests performed on a migratory p opulation of T. sirtalis. Navigational skills vary little between migr ating and nonmigrating populations of the same species but may be poor ly developed in nonmigratory species.