Female mimicry in garter snakes: behavioural tactics of "she-males" and the males that court them

Red-sided garter snakes (Thamnophis sirtalis parietalis) in central Manitoba court and mate in early spring soon after emerging from communal overwintering dens. Some males ("she-males") produce female-like skin pheromones, and hence attract courtship from other males. Studies at a den near Inwood, Manitoba, support and extend results from work at other dens. She-males were males that had recently emerged from hibernation and had not yet regained full locomotor capacity or muscle strength. She-males resembled "he-males" rather than females in their antipredator responses, including the thermal threshold at which they fled from a simulated predator (a plastic crow) rather than remaining stationary and displaying. Males courting she-males were cooler than those courting females; nonetheless they were more likely to flee when we approached them. Compared with courting groups focussed on females, groups around she-males were smaller, consisted predominantly of smaller he-males, and were found over a more restricted time of day (early afternoon). Arena trials confirmed that she-males are disproportionately courted by small rather than large he-males, and clarified other aspects of she-male attractiveness and behaviour. She-males attracted more intense courtship when large females were absent. She-males courted less vigorously when large he-males were present, especially when they were vigorously courted themselves. Overall, our data reveal hitherto-unsuspected complexity in the behavioural tactics of reproducing garter snakes.