Brain size is a key factor determining the performance and fitness of an organism; birds with relatively larger brains might have advantages in the utilization of resources and dispersal. Bite force is another important indicator of fitness, and plays an essential role in intra- and inter-specific competition. In this study, a comparative analysis was conducted on the head size and bite force of the two sister species, the white-rumped munia (Lonchura striata) and scaly-breasted munia (L. punctulata) that differ in distribution range. The results showed that the scaly-breasted munia, which has a wider distribution range, had a significantly larger head size than that of the white-rumped munia. In addition, scaly-breasted munias had a greater bite force; however, the difference was not significant. One possible explanation could be that the smaller head to body ratio in scaly-breasted munias reduced their bite-force slightly. Further, this finding could be attributed to the fact that similar food resources and foraging habitats of the two species lead to a similar bite force. Our study supported the argument that head size, rather than bite force, plays a more important role in the dispersal and evolutionary adaptation of birds.
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