Fig. 11. Mean efficiency of sound production E for individuals of each species. There were no statistically significant differences in E between individual S. borellii. One S. vicinus had a mean E significantly lower than the others. In both species the major cause of variation in E was that P_ac was generally more variable than P_call. Overall E was significantly greater in S. borellii than in its congener. Values are means ± 95% CI.