The split screen tool of ‘slope’ (measured in Octaves per Second OPS) in Analook for Windows can be used as an aid to identification of Myotis species and the three ‘big bat’ species.
By right clicking on the slope screen, ‘transition’ options are displayed as well as a default ‘auto’ option. Try different ‘transitions’ to see how the slope appearance changes and then stick to one transition option for all comparisons. The examples given here are all depicted using the ‘auto’ option.
Although all species have slope characteristics, the slope parameters can change, even for the same species, depending on the physical characteristics of environment the bat was flying in (e.g. clutter or non-clutter). The examples given compare five UK Myotis species with one another and the two Nyctalus and Eptesicus species with one another, all based on ‘clear air flying’. It is advised that rather than take quantitative measures of slope to determine species, a call library of species flying in different environments should be collected and used for direct comparison to the unidentified calls by opening two comparable Analook screens.
It is not possible to be definitive about Myotis species (and in some cases Eptesicus and Nyctalus species), unless you have the bat in the hand. However you can report that the unidentified call ‘has the characteristics of ………..(species), based on comparison with a known call sequence from a bat flying in a similar situation.’ Then insert a comparison table of slope, call duration, IPI and characteristic frequency parameters measured from the library call and the unidentified call.