Fig. A1. (A) Effect of efficiency of conversion of metabolic energy to mechanical work against gravity and (B) mass of spoil (expressed as % of body mass) carried in each trip to the surface on total burrow construction cost for Notomys alexis. Filled symbol represents spoil mass used in model calculations (4.4% and 25% for conversion efficiency and spoil mass, respectively; total burrow cost=55.5 kJ).