Behavioral shifts associated with reproduction in garter snakes

Reproduction may involve profound modifications to behaviors such as feeding, antipredator tactics, and thermoregulation. Such shifts have generally been interpreted as direct consequences of reproduction but may instead be secondary effects of reproduction-associated changes in other traits such as habitat use. We quantified behaviors of red-sided garter snakes (Thamnophis sirtalis parietalis) courting and mating at a communal den, and also of postreproductive snakes dispersing from the same den. Snakes at the den actively courted, did not feed, tolerated close approach by humans, and did not retaliate (bite) when seized by us. Dispersing snakes did not court, fed, fled from our approach, and bit when seized. Snakes of both groups were then transferred to outdoor arenas and retested. Courtship vigor by males, and attractiveness of females, had declined but not disappeared for the dispersing snakes. Snakes of both groups ate readily, showing that reproduction-associated anorexia was a facultative response to lack of prey in the den. Body temperature regimes were also similar in the two groups of snakes. Overall, many of the characteristic behavioral changes associated with reproduction were responses to features of the den environment (e.g., presence of sexual partners, lack of food) rather than to reproduction per se. The shift in antipredator responses, however, may reflect a neural or endocrine "switch," suggesting that the link between reproduction and other behaviors involves a diversity of proximate mechanisms.