Reproductive effort and reproductive nutrition of female desert tortoises: essential field methods

I used three innovative, nondestructive field methods (gas dilution,doubly labeled water and radiography) to measure individualenergy and water budgets of wild, female desert tortoises (Gopherusagassizii). With these budgets, I evaluated whether body reserveshelp females produce eggs independent of rainfall and food availability.Female desert tortoises used large seasonal and annual changesin metabolism and body water, protein and energy reserves tosurvive and produce eggs. Although lipid reserves are importantto female desert tortoises, nitrogen or crude protein appearsto be the primary limiting resource for producing eggs. By reducingmetabolic rates 90%, females conserved enough body reservesto produce eggs during extreme drought conditions; this is aneffective bet-hedging reproductive pattern in an extreme andunpredictable environment.