Finds harbor porpoise feeding buzzes

This function uses one of two methods to classify NBHF clicks into one of two classes: feeding buzz or non feeding buzz.

Usage

fp_find_buzzes(x, method = "clicks")

Arguments

x

a data.table where each row is a click, as the "clicks" element in the list object returned by fp_read(). Each row must minimally have a POSIXct column time, with nanosecond precision.

method

the method to use to find feeding buzzes - "clicks" or "trains". See details.

Value

An integer vector of the same length as nrow(x), where the values indicate that that click can be considered a feeding buzz (value = 1) or not (value = 0).

Details

Note that the so-called "feeding buzzes" are usually considered to represent a combination of feeding buzzes and social calls. Even so, the classifications resulting from both of these methods are commonly used as a proxy of foraging activity.

The two available methods are:

• clicks method: any inter-click-interval (ICI) less than 20 milliseconds is considered a NBHF feeding buzz.

• trains method: buzzes are identified using a mixture Gaussian model, with the number of components k=3. All clicks associated with the first component are considered a NBHF feeding buzz. This method requires the package mixtools to work.

References

Pirotta, E., Thompson, P.M., Miller, P.I., Brookes, K.L., Cheney, B., Barton, T.R., Graham, I.M. and Lusseau, D. (2014), Scale-dependent foraging ecology of a marine top predator modelled using passive acoustic data. Funct Ecol, 28: 206-217. https://doi.org/10.1111/1365-2435.12146

Examples

# first read some FPOD data
fn <- fp_example("gullars_period1.FP3")
dat <- fp_read(fn)

# extract porpoise clicks of quality Hi and Mod
nbhf <- dat$clicks[species == "NBHF" & quality_level >= 2]

# then add a 'feeding buzz' column to the clicks data.table
nbhf$buzz <- fp_find_buzzes(nbhf, method = "clicks")