Inferring an animal's environment through biologging: quantifying the environmental influence on animal movement

Abstract

Background: Animals respond to environmental variation by changing their movement in a multifaceted way. Recent advancements in biologging increasingly allow for detailed measurements of the multifaceted nature of movement, from descriptors of animal movement trajectories (e.g., using GPS) to descriptors of body part movements (e.g., using tri-axial accelerometers). Because this multivariate richness of movement data complicates inference on the environmental influence on animal movement, studies generally use simplified movement descriptors in statistical analyses. However, doing so limits the inference on the environmental influence on movement, as this requires that the multivariate richness of movement data can be fully considered in an analysis.Methods: We propose a data-driven analytic framework, based on existing methods, to quantify the environmental influence on animal movement that can accommodate the multifaceted nature of animal movement. Instead of fitting a simplified movement descriptor to a suite of environmental variables, our proposed framework centres on predicting an environmental variable from the full set of multivariate movement data. The measure of fit of this prediction is taken to be the metric that quantifies how much of the environmental variation relates to the multivariate variation in animal movement. We demonstrate the usefulness of this framework through a case study about the influence of grass availability and time since milking on cow movements using machine learning algorithms.Results: We show that on a one-hour timescale 37% of the variation in grass availability and 33% of time since milking influenced cow movements. Grass availability mostly influenced the cows’ neck movement during grazing, while time since milking mostly influenced the movement through the landscape and the shared variation of accelerometer and GPS data (e.g., activity patterns). Furthermore, this framework proved to be insensitive to spurious correlations between environmental variables in quantifying the influence on animal movement.Conclusions: Not only is our proposed framework well-suited to study the environmental influence on animal movement; we argue that it can also be applied in any field that uses multivariate biologging data, e.g., animal physiology, to study the relationships between animals and their environment.

Leveraging similarity analysis to understand variability in movement behavior

“…That motivates researchers to analyze and infer the environmental drivers leading to variability in animal movement. In previous studies, inferring environmental drivers is often accomplished through relating movement parameters (MPs), such as animal activity space and speed and turning angles, directly to a set of environmental variables (Dodge et al, 2014; Eikelboom et al, 2020; Patterson et al, 2009). Those studies view the same species as a whole while neglecting the individual differences of preferences on environmental context.…”

“…It is believed that patterns of human mobility are linked to how people influence their spatial context and how the spatial context influences them in return (Palmer et al, 2013). The same applies to animal movement ecology, especially that movement is arguably the most significant way by which animals respond to changes in their surrounding environment (Eikelboom et al, 2020; Nathan et al, 2008). That motivates researchers to analyze and infer the environmental drivers leading to variability in animal movement.…”