22 Tracking data: Brief introduction

This chapter was built with R version 4.3.2 (2023-10-31 ucrt)

The chapter was last updated on 2024-02-23

22.1 Animal tracking data considered in this toolkit

This toolkit focuses on the analysis of data primarily from GPS and PTT devices. Some of the analyses may be extended to data from GLS devices. For all devices, we encourage users to understand the limitations of each device and how these limitations can affect interpretation of animal movement patterns.

22.2 General introduction to animal tracking data

Distribution data can be obtained from observations collected during surveys within a predetermined spatio-temporal frame of reference or by sampling locations of individual animals using animal‐borne tracking devices. The former provide an area-based sampling perspective, also referred to as a Eulerian perspective in the oceanographic literature, whereas the latter provides an individual based sampling perspective, also referred to as a Langragian perspective (Phillips et al. (2019)).

Area-based or Eulerian survey designs sample across a predetermined survey area using predetermined sampling locations or transects, which may or may not be replicated through time. The primary objective of this sampling approach is to obtain animal distribution and abundance data in a predefined area and time period. For seabirds, at-sea such surveys are generally conducted using ships or aircraft (Buckland et al. (2012); Camphuysen et al. (2004); Tasker et al. (1984)), although land-based surveys may be used to cover near-shore environments (Arranz et al. (2014); Smith et al. (2015)).

Individual-based or Lagrangian survey designs track the locations of seabirds and other marine megafauna through space and time using data logging or tracking devices attached to individuals (Burger and Shaffer (2008); Hays et al. (2019)). Location data may be received in near real-time from transmitting or satellite-linked devices, or obtained by downloading stored location data using base-stations or after device retrieval. Depending on the mobility of a species, individual-based sampling may increase the spatial extent and resolution of the survey area compared to area-based surveys, or even identify colony location and/or at-sea habitats if no a priori information about species movements are available (Bolton (2021)).

Modern tracking methods provide high‐resolution data (generally with sub-km precision) at an individual level, but device cost and the logistical challenges of tag deployment usually limit the number of tags deployed, as well as the number of locations at which tags are deployed. So while the spatial extent of survey coverage achieved by animal-borne devices is determined by individual’s movements, and not a priori defined by the surveyor, achieved coverage of the wider marine environment will generally not be independent of the locations at which tracking devices are deployed. Tag deployment further depends on the accessibility and/or catchability of individuals, therefore tracking data sets often exhibit individual-level heterogeneity, which may be related to sex, age, breeding status and/or colony-affiliation (Gutowsky et al. (2015); Krietsch et al. (2017)) and may complicate population‐level inferences.

Some of the limitations identified above should be accounted for by users when defining the “dataGroup” for analysese following the track2kba protocol outlined in this toolkit.