Decreased food intake as a fecundity-dependent cost of reproduction in keelback snakes ( <i>Tropidonophis mairii</i> , Colubridae)

The physical burden of pregnancy may render females slower and less able to evade predation, favouring a reduction in feeding in order to avoid a reduction in survivorship. Life-history theory predicts that an organism's optimal level of investment into reproduction depends upon whether or not the associated 'costs' (such as a decrease in rate of feeding) increase with higher fecundity. Anorexia during pregnancy is widespread among snakes, but there are few field data on fecundity-dependence of such costs. Over a 23-year period, we recorded reproductive condition and feeding status (based on palpation and production of faeces) for 3778 captures of free-ranging female natricine colubrid snakes (keelbacks, <i>Tropidonophis mairii</i>) in tropical Australia. Pregnancy reduced feeding rates, and that decrease was greatest for females with higher reproductive investment (clutch mass relative to maternal mass). Our long-term data provide the first clear-cut evidence of fecundity-dependent costs of reproduction in free-ranging snakes.