Mate location tactics in garter snakes: effects of rival males, interrupted trails and non-pheromonal cues

1. The ability to follow substrate-deposited scent trails using sophisticated vomeronasal abilities is a key feature of snake biology. However, previous research on this topic has derived mostly from a highly artificial test situation: captive snakes following continuous trails over structurally simple homogeneous substrates, in the absence of any other cues (e.g. visual or olfactory) either from the target of that search or from other snakes. 2. Our field experimental trials with Red-Sided Garter Snakes (Thamnophis sirtalis parietalis) at a communal den in Manitoba explored wider issues in mate location. 3. Males followed a female's trail less successfully if she had recently been followed by rival males, suggesting that trailing males obscured the cues left by the female. 4. Males that lost contact with a female's trail exhibited stereotyped, spatially extensive and prolonged circling behaviour centred on the last point at which the trail was detectable; in nature, this behaviour would maximize the male's ability to relocate a discontinuous trail. 5. Trail-following males switched from chemical to visual cues as soon as they were close to a female, enhancing speed but decreasing the accuracy of mate location (because males could distinguish between females and other males based on either visual or airborne olfactory cues). 6. Incorporating additional cues and broader spatial scales can clarify aspects of trail-following behaviour not evident from studies in small, highly simplified laboratory situations.