Data Processing

Firetail features a several data processing and data visualisation tools. You can access these features via the Data menu.

Overview

(see below for details)

Menu Item	Category	Description
Default Color	Color Track by	Use the default color for the trajectory.
Point Index	Color Track by	Highlight timestamps by an equidistant index. Time intervals are neglected.
Timestamp	Color Track by	Highlight timestamps with respect to the time intervals among them.
Speed over Ground	Color Track by	Highlight each timestamp by measured speed over ground.
Height	Color Track by	Color each timestamp relative to its associated height
Temperature	Color Track by	Show the measured temperature for each timestamp
Battery Voltage	Color Track by	Show the voltage available to the tracking device for each timestamp
DBBMM Average Window Variance *)	Color Track by	show the track's utility distribution calculated from a dynamic Brownian Bridge Movement Model
Location Data Smoothing Layer	Manipulate Locations	apply curve smoothing trajectory
Kernel Density Map	Analyze Data	compute heatmaps based on frequency of occurrence
Show Convex Hull	Analyze Data	show the minimal convex polygon around the data
Calibrate e-obs IMU Data	Analyze Data	calibrate Inertial Measurement Unit data for e-obs tags
Calculate DBBMM	Analyze Data	calculate a dynamic Brownian Bridge Movement Model

*) Requires Calculate DBBMM

Point Index/Timestamp

In the default viewport there no indication is given whether a timestamp has been measured earlier, or later. Using point index or timestamp will visually highlight early (black) points from late (white) measurements. While the point index uses equally distributed colors along the complete track, the timestamp mode will scale the colors according to their distance.

Speed/Height/Temperature/Battery Voltage

The respective attribute is color-coded by its maximal (white) and minimal (black) values for each timestamp.

DBBMM

The dynamic brownian bridge movement model provides means to estimate the utility distribution from a set of locations and timestamps. It was originally published by Kranstauber et al., 2012 [1] as a combination of Brownian Bridges (Horne et al., 2007 [2]) and behavioural change pattern estimation (Gurarie et al., 2009 [3]).

Firetail computes the utility distribution for one selected individual via Data > Location and GPS > Calculate DBBMM. The induced heatmap can be shown by Data > Location and GPS > DBBMM Average Window Variance.

The heatmap and the Average-window-variance sensor-type can be hidden from the map via Data > Clear Overlays.

Kernel Density Map

see Kernel Density Estimation

Location Smoothing

Animal tracks can be smoothed to approximate real-life flight patterns and movement routes.

Each fix is replace by the average of its location and that of its trajectory neighbors. Notably, this feature will displace the current trajectory significantly. It is useful to simulate more natural movement patterns at the cost of actual measurement accuracy.

Outlier Filtering

Movebank outlier definition

Movebank provides the following categories for tagging data outliers that Firetail will interpret as well in the context of csv and Movebank files.

field	description
manually-marked-outlier	manually assigned outliers
import-marked-outlier	externally assigned outlier
algorithm-marked-outlier	outliers assigned by the Movebank algorithm
manually-marked-valid	override outlier assignment (force include)

Fields that contain one of the following values will be considered true during read-in: {"1", "true", "t", "yes", "y"}.

In the Firetail settings, enable the Movebank outlier filter via

File > Settings > Import, then check filter outliers by annotation (manual/import).

Status/type outliers

Typically, fixes are filtered that differ from

field	value
type-of-fix	3
status	A

This option is targeted at e-obs tags and forces the inclusion of filtered measurements. Enable this filter in

File > Settings > Import > Filter Outliers by status/type

Hint: combine this filter with a speed threshold filter or Movebank annotation filters

Speed threshold filter

During read-in, this filter checks for each position if it is reachable from the previous location given a user-defined maximum speed threshold. Enable this filter in

File > Settings > Import > Filter Outliers by speed threshold

Show Convex Hull

Draw the minimum convex polygon around each grouping (tag/individual/deployment). If a visible region around the current timestamp is selected (dropdown menu below time slider), the induced time window is used to restrict the data.

An area statistics window will show the (approximate, no earth-curvature) area of the shown regions for all selected (Open Files) regions.

Overall dynamic body acceleration

Overview

The overall dynamic body acceleration (ODBA) is a measure derived from acceleration data. It can be used to estimate energetic costs of different behaviours, i.e. following Wilson et al. [4] the value is correlated linearly to the oxygen consumption and CO2 production.

Computing ODBA

ODBA can be computed when acceleration data is available.

1. Open a project with associated acceleration data
2. Select Data > Acceleration > Compute ODBA

Additional lanes will be shown containing a visual representation of the ODBA results per grouping, i.e. per acceleration source. In addition to the overall mean ODBA the individual axis mean values are shown as well.

Exporting ODBA values

ODBA can be exported along with accelerometer data along with other auxiliary data by File > Export Annotated Events > Export Acc Bursts as CSV .

One file will be created per grouping (individual/tag/deployment). You'll be asked where to save each file.

Key steps

Firetail computes the ODBA value as follows:

1. calculate a mean acc value for each direction and each burst
2. substract the respective mean from each measurement
3. sum over the absolute value across all directions

Details

Let $B$ a burst of $n$ samples.

A burst sample $b_i = (x_i, y_i, z_i),\,i=1 \dots n$ holds the respective x, y and z acceleration components.

Given the mean values

$$\overline{x} = \frac{\sum_{i=1}^n{x_i}}{n}\newline{} \overline{y} = \frac{\sum_{i=1}^n{y_i}}{n}\newline{} \overline{z} = \frac{\sum_{i=1}^n{z_i}}{n}$$

the overall dynamic body acceleration is then given by

$$ODBA(B) = \sum_{d \in \{x,y,z\}}{|d_i - \overline{d}|}$$

A similar value is computed for activity plots.

Activity Value

The activity value is a time-dependent measure summing over the absolute difference of consecutive values in a burst.

Let $B$ a burst of $T$ ordered samples in dimensions $x, y$ and $z$.

Activity ACT(B) is then defined as:

$$\text{ACT(B)} = \frac{1}{3 * (T - 1)} \sum_{t=1}^{T} \left( |x_{t-1} - x_{t}| + |y_{t-1} - y_{t}| + |z_{t-1} - z_{t}| \right)$$

References

1. Kranstauber, B., Kays, R., LaPoint, S. D., Wikelski, M., & Safi, K. (2012). A dynamic Brownian bridge movement model to estimate utilization distributions for heterogeneous animal movement. Journal of Animal Ecology, 81(4), 738-746.
2. Horne, J. S., Garton, E. O., Krone, S. M., & Lewis, J. S. (2007). Analyzing animal movements using Brownian bridges. Ecology, 88(9), 2354-2363.
3. Gurarie, E., Andrews, R. D., & Laidre, K. L. (2009). A novel method for identifying behavioural changes in animal movement data. Ecology letters, 12(5), 395-408.
4. Wilson, R.P., White, C.R., Quintana, F., Halsey, L.G., Liebsch, N., Martin, G.R. & Butler, P.J. (2006) Moving towards acceleration for estimates of activity‐specific metabolic rate in free‐living animals: the case of the cormorant. Journal of Animal Ecology, 75, 1081–1090.