A description of the acoustic method used to discriminate between different species of Myotis bats developed by Michel Barataud
The south-eastern part of France is one of the richest areas of Europe when it comes to species of bats. One can expect to pick up nearly all european Myotis bats in some regions, and many of them on a regular basis. This makes the identification of species extremely cumbersome, so the locals are forced to work hard on the problem of how to distinguish different species on the basis of their echolocation calls. After having followed a workshop and by using a power point presentation designed by Michel Barataud, I would like to describe the new method in english. If you think I made a mistake in explaining the method, please send me a mail to correct my text. In some time I will analyse the example-calls of the power point presentation and present here the results of my attempt to extract the physical parameter that represent the cues Michel Barataud and many other people in France use.
The Barataud-method consists of three stages:
1: Define the structure of the calls.
This basically boils down to determining whether we are dealing with calls of Myotis dasycneme, or any of the other Myotis bats. Long (>10ms), narrowband calls would suggest M. dasycneme, anything else all other Myotis.
2: Listen to the sequence and try to establish whether you hear A an "amorce", B a "claquement final" or C none of the two: absence de pic.
Note that C really means neither A nor B and forget about the word "pic". Below you can read what amorce and claquement final mean.
3: Classify the end frequency as either A: high (>30kHz), B: average (23-30kHz), or C: low (<23kHz). We are supposed to do this by listening, but I guess it wouldn't hurt to at least check our perception with Batsound.
The three-point system works like a key. For instance, if you go through stage 1 and eliminate dasycneme, then in stage 2 you hear neither A nor B and your end frequency is above 30 kHz, the only species you are left with are: M capaccini, M. emarginatus and M nattereri (the last species, apparently CAN end a bit higher than it usually does). The three-point therefore tells you the GROUP of Myotis bats you are dealing with. You need the Barataud-tables (that are available as presentations, and will be published soon) to go down to species level. Take for example the group "claquement final, haute fréquence". This can only be: M. emarginatus, bechsteini and brandtii. Now, imagine end frequency is 45 kHz. According to a graph, this can only be M emarginatus. Had duration been 2.5 ms and end frequency 37 kHz, no further conclusion could have been drawn. I understand that this doesn't help you very much now, not having the Barataud-graphs, but I am just trying to explain the method here and nothing more. To be complete about it all I would like to list the parameters that are used to draw the exclusion-graphs: pulse duration, end frequency, bandwidth and frequency of maximum energy (frequency at which the FFT over the entire pulse has its peak). The parameter "bandwidth" implies that the start frequency of pulses is also measured, since bandwidth is start frequency - end frequency.
Amorce and claquement final
By now you should have some impression of the three-point system. Still, we don't know what amorce and claquement final mean. According to my dictionary amorce means "upbeat" and during the workshop I attended, it was explained that amorce refers to a sound quality at the BEGINNING of a pulse and claquement final to a sound quality at the END of each pulse. It was explained that we don't yet know what either parameter mean in physical terms, but listeners (after training) firmly agree on whether the parameter in question is present or not. People said the sound quality (some kind of clicking, or impression of 'suddenness') MAY be related to the steepness of the upgoing and downgoing slope of the oscillogram. However, it was also said that the sound quality "amorce" may well be impossible to visualise on Batsound.
This is my description of the Barataud-method. Please let me know if you feel that the text above needs some modifications. Being a very critical person, I fear to have annoyed some of the organisers of the workshop that I attended, but I promised to at least make an effort to find the physical parameters that are most strongly correlated with amorce and claquement final. As soon as I have some results, I will present them here.