- 1. Small mammals require more energy per unit gut capacity than large mammals and, as a result, are forced to be more selective in their dietary habits. We predicted that when offered seeds, Meriones crassus (adult body mass [m b ] = 50-100 g) would husk less and consume proportionately more husks than the smaller Gerbillus henleyi (m b = 8-12 g). Furthermore, in the sexually dimorphic M. crassus, larger males would consume proportionately more husks than females but in G. henleyi, which does not show size difference between sexes, there would be no difference in husk intake. 2. Only male M. crassus (m b =86 2g) consumed husks ; female M. crassus (m b =57.0g) and both sexes of G. henleyi (m b =9.20g for males and 8.85g for females) did not. Therefore, our hypotheses were partly supported. 3. Digestibilities of dry matter and energy for male M. crassus were lower than for females and those of G. henleyi males and females. This was a result of the greater proportional consumption of low digestible, low energy husks. 4. We also predicted that the average daily metabolic rates (ADMR) of these species would be (1) similar to each other when compared allometrically and (2) lower than those predicted for rodents of their body masses. These hypotheses were based on the coexistence in deserts and similar granivorous diets of the two gerbil species. ADMR for each species was calculated from the regression equation of body mass change on metabolizable energy intake at the point of zero change in body mass. 5. Their ADMRs, 8.23kJ g -0.54 day -1 for M. crassus (m b =72.6g) and 8.65 kJ g -0.54 day -1 for G. henleyi (m b =9.05 g), were similar and therefore this hypothesis was confirmed. However, in contrast to our hypothesis, both these species had ADMRs that were similar to predicted values, that is, 96.1% and 101.1%, respectively, of rates predicted for their body masses.