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, Tropidonophis mairii) 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.

Mark-recapture data from adult female snakes during the April - July nesting seasons from 1998-2021. Data include female ID number, snout-vent length (SVL), body mass, postpartum body mass (PPM) and relative clutch mass (RCM). n/a indicates missing data.