Animal Movement - Mobility Data - page 274

revolution that has enormously spurred the study of animal movement was the
advent of GPS-based devices to track animals (Cagnacci et al., 2010).
In parallel with technological and experimental developments there was an
improvement of the statistical methods necessary to study spatial and temporal
processes. In Chapter 1 , a raw trajectory is described by a list of tuples containing
mainly the instant and point of the moving object. In this chapter we use another
representation, a list of vectors, each one (in a 2D space plus time) characterized
by angle and distance. However, the statistical analysis of angles is challenging
because it requires a specific approach, because angles are defined in the interval
− π and + π and appropriate distributions are obtained by wrapping conventional
linear distributions (i.e. − π =+ π ,or2 π = 0). A relevant improvement was
represented by the use of the use of circular statistics in the study of animal
orientation. The first compendium on the modern analysis of biological diffusion
was due to Okubo, although Turchin provided a comprehensive theoretical
summary. The discipline studying animal paths is referred to as trajectometry .
The literature about animal movement is double-faced: the newcomer to this
field has to be aware that two different approaches are used. Many scholars
investigate the proximate causes of movement, for instance, which orienting
cues an animal uses to move from point A to B. On the other hand, researchers
are interested in the ultimate causes of movement, for instance, which are the
factors causing the size of one animal's home range. Indeed, there is not a clear
separation between the two approaches and today the use of complex statistical
modeling makes it possible to investigate both levels of causation within the
same framework. Studies on animal movement have to be directly linked to evo-
lutionary theory, species life history, and the ecological modulation of behavior.
The aim of this chapter is to give a presentation of the state of the art in
the study of animal movement, which could help the student or the beginner to
orient him or herself in this rather cumbersome field of research. In this chapter
we try to avoid as much as possible mathematical formulations and we will use
verbal models and simulations to illustrate the main concepts. Thus the reader
can (1) use this chapter as an introduction to more complex and mathematically
demanding papers, or (2) grasp the main concepts in order to better plan data
collection and experiments and to acquire concepts and terminology useful to
foster cooperation with statistical and mathematical experts.
13.2 The Study of Animal Movement
13.2.1 A Revolution: Biologging Technology
The simplest method to study animal behavior is to use individually recognizable
tags, such as rings, collars, and ear tags. The results obtained by tags are prone to
bias, due, for instance, to differences in recovery rates (in times and/or space) or