Referee 1's review (Brock Fenton):

**********
N.B. These are the comments made by the referee when reviewing an earlier version of this paper. Prior to publication the manuscript has been revised in light of these comments and to address other editorial requirements.
**********

Review of the original submission:
This is an excellent paper. The experiments, analyses and statistics are of high quality and the conclusions are presented in a user-friendly way. The authors have provided enough detail to allow someone to replicate their work. The writing is clear and the paper does not duplicate anything else that the authors have published (although it builds effectively on their previous work). There are no ethical issues.

I have one suggestion I believe to be important. The authors should present their findings in an evolutionary setting. I recommend including a recent phylogeny of bats (perhaps that of Jones and Teeling in TREE) to make an evolutionary argument. This will increase the impact of the work both for those who study bats and those who are interested in the more general application.

The authors might be clearer about "the range of echolocation" ... the range over which a bat can detect an insect-sized target.

I am not convinced that abbreviations such as SL enhance the manuscript. The term is first introduced on page 4 (although it is mentioned at the beginning - abbreviations. For the few words it adds, I would write it out rather than use the abbreviation (if the goal is to make the information accessible to people outside the bat and sound community.
This is an excellent contribution.

Review of the first revised manuscript:
I have reviewed the revised manuscript and recommend that it be accepted for publication. The authors have addressed my main comment which was putting the information in an evolutionary context and perspective. Given the paper that appeared yesterday in Nature (Simmons et al. 2008), the authors might consider adding a reference to this latest and perhaps most astonishing fossil bat.

Very nice manuscript.