D7 Environmental and Contextual Analysis

Topic

Environmental and contextual analysis quantifies the physical conditions of the environment in which the mammal operates, as well as the animal's interactions with that environment over time and space. To achieve this, it integrates four components: tracking technologies that monitor the animal's position, techniques for characterizing the surfaces it traverses, measurements of surrounding climatic variables, and a quantitative analysis of its social behavior—all of which provide the physical context for the animal's movement and physiology.

Tracking technologies combine a satellite positioning system with an inertial unit consisting of an accelerometer, a gyroscope, and a magnetometer—each measuring along the three spatial axes; together, these sensors record the animal's geographic position and movement at high frequency. Integrating the accelerometer's acceleration data twice over time yields the animal's displacement, although this calculation accumulates increasing error over time; to correct this, a sensor fusion algorithm combines satellite positioning—which updates infrequently but does not accumulate error—with inertial measurements—which update frequently but do accumulate error—thereby obtaining the best possible estimate of the animal's dynamic state at any given moment. Data from the accelerometer, combined with empirically derived calibration models, also allow for the estimation of the dynamic power the animal generates in the field.

Characterizing the surfaces the animal traverses involves three distinct measurements: the surface's coefficient of friction, obtained by dragging a test element across it; substrate stiffness regarding deformation, obtained by pressing a test element against the surface; and surface roughness, obtained by tracing its profile with a precision instrument. The quantitative analysis of social behavior mentioned at the beginning represents each animal in the group as a point within a network, and each physical interaction between two animals—such as contact, a chase, or a vocalization occurring within a certain maximum distance—as a connection between those two points; this connection is weighted according to the intensity or frequency of the interaction. The number of interactions each individual maintains with its nearest neighbors follows a characteristic distribution within the group, and this distribution makes it possible to identify individuals who are isolated from the social network or who exhibit an interaction pattern that is anomalous compared to the rest.

The animal's daily energy expenditure, estimated from the dynamic power calculated via accelerometry, correlates with body mass according to the same allometric relationship observed in basal metabolism: it does not increase in direct proportion to mass, but rather according to a power of mass slightly less than one. Superimposed on this basal metabolism, the animal's locomotor activity adds a multiplier ranging from one-and-a-half to eight times the basal expenditure, depending on the intensity of the activity; thus, the environmental and contextual analysis that introduced this description ultimately explains—through the physical context of movement—a substantial portion of the animal's total energy expenditure.

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