Vigie-Chiro
French reference scales of activity levels
Summary
These tables can be used by bat workers and enthusiasts, consultancies and conservation practitioners to compare their study site with a national reference and conclude on the importance of their site for bats. This can answer questions such as: "Is bat activity higher than the national/regional mean on my site?" or "Do my recordings reveal conservation issues? And on what species?" or "Is this habitat of higher quality for bats than expected?", etc.
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We made these tables available for a variety of geographical areas and habitats in France, but we strongly recommend to first use the national reference scale since it is both the most robust one and the most relevant for conservation, and then complete the analysis with other reference scales if needed.
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We built those reference scales of activity based on the method developed by Alexandre Haquart (2015).
How the reference scales were built
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Bat acoustic activity has a non-normal distribution. This means that for each night of recording, it is more common to record a few bat passes, while nights with a lot of bat passes are rarer. Therefore, we need to take this into account to establish levels of activity (low, medium, high, very high). This is why we use quantiles to define the thresholds between the activity levels.
To do this, we order all the nights available in our database (Vigie-Chiro French Bat Acoustic Monitoring Program) from the night with the lowest to the night with the largest amount of bat passes. We then calculate the quantiles at 25%, 75% and 98%. To give an example, if Q25% = 3 bat passes/night, this means that 25% of nights have a value that is inferior or equal to 3.
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This is done for each species separately.
How to use the reference scales
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You need to have a study site in France (or at least close to the border) to use these reference scales. Your bat recorder and its settings must match the requirements of the Vigie-Chiro protocol.
Calculate the count of bat passes per night on your study site. One bat pass is defined as 1 or more than 1 bat call in a time frame of 5 seconds. Once you have calculated the count of bat passes/night for a given species on your own study site, refer to the values in the three columns (Q25, Q75 and Q98). Determine between which thresholds your value is, and assign the corresponding level of activity. We defined activity levels as following:
Density
Number of bat passes/night
Example of quantiles calculated for the common pipistrelle
Be aware that the number of observations used to build the reference scale (our database, not yours) is a very important factor of reliability. It means that for species or habitats that were undersampled we cannot provide reliable activity level thresholds ! A dedicated column "confiance" (confidence in french) is provided in the tables for this purpose.
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Therefore, each person contributing to Vigie-Chiro helps to reinforce the reliability of the reference scales. Regular updates will be made and these tables will thus progress in reliability year after year.
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Since acoustic sequences are automatically identified with the TADARIDA software, we used a method to automatically sort out false positives (see Barré et al., 2019). This process does not guarantee the absence of abnormal data (e.g. Mediterranean species found in Northern France). However, the error rate is small enough to provide reliable results using the associated confidence information.
Definition of the table columns
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MoySiP: Mean number of bat passes per night if the species is present during the night
EtypSiP: Standard deviation of bat passes per night if the species is present during the night
Q25, Q75, Q98: 25%, 75% and 98% quantiles
nbocc: Number of nights where the species was present
Confiance: Confidence (directly linked to nbocc)
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Downmoad the French national reference scale of activity levels
Download the reference scales for different habitats and biogeographical areas
Download the definition of each reference scale name
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Quantiles
Activity level
< Q25
Low
Q25 - Q75
Medium
Q75 - Q98
High
> Q98