A new direction for differentiating animal activity based on measuring angular velocity about the yaw axis

Abstract

The use of animal‐attached data loggers to quantify animal movement has increased in popularity and application in recent years. High‐resolution tri‐axial acceleration and magnetometry measurements have been fundamental in elucidating fine‐scale animal movements, providing information on posture, traveling speed, energy expenditure, and associated behavioral patterns. Heading is a key variable obtained from the tandem use of magnetometers and accelerometers, although few field investigations have explored fine‐scale changes in heading to elucidate differences in animal activity (beyond the notable exceptions of dead‐reckoning). This paper provides an overview of the value and use of animal heading and a prime derivative, angular velocity about the yaw axis, as an important element for assessing activity extent with potential to allude to behaviors, using “free‐ranging” Loggerhead turtles ( Caretta caretta ) as a model species. We also demonstrate the value of yaw rotation for assessing activity extent, which varies over the time scales considered and show that various scales of body rotation, particularly rate of change of yaw, can help resolve differences between fine‐scale behavior‐specific movements. For example, oscillating yaw movements about a central point of the body's arc implies bouts of foraging, while unusual circling behavior, indicative of conspecific interactions, could be identified from complete revolutions of the longitudinal axis. We believe this approach should help identification of behaviors and “space‐state” approaches to enhance our interpretation of behavior‐based movements, particularly in scenarios where acceleration metrics have limited value, such as for slow‐moving animals.

Similar circling movements observed across marine megafauna taxa

“…Circling movements may be an effective strategy for collecting navigational cues, such as visual, olfactory and magnetic information, etc. Similar mechanical circling movement was also reported in a post-nesting loggerhead turtle (Caretta caretta) that circled 17 times in 3.75 min during the flat-bottom phase of a U-dive, although the geographic location of this circling behavior is unknown (Gunner et al, 2020).…”

Hidden Markov models identify major movement modes in accelerometer and magnetometer data from four albatross species

“…The frequency and amplitude of cycles that characterize dynamic soaring [ 56 ] could reveal how birds adjust soaring when responding to environmental cues, such as wind variability. Novel metrics derived from magnetometer data, such as the recently described AVeY (angular rotation about the yaw axis) may prove to be equivalent, or better, proxies of energy expenditure for soaring birds than traditional accelerometer-derived metrics such as ODBA [ 22 ], given the energetic cost associated with body rotations [ 57 ].

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“…Tri-axial magnetometers record movement data that are analogous and complementary to that of accelerometers and are being deployed with increasing frequency [ 20 – 22 ]. These sensors record magnetic field orientation and intensity, from which animal heading and angular velocity about the yaw-axis can be derived.…”

Dead-Reckoning Animal Movements in R – A Reappraisal Using Gundog.Tracks

“…[62], for recent review) has been validated as a proxy of speed for terrestrial animals [63,64] although there are still very few studies that use the dead-reckoning method in terrestrial animals [e.g., 6,7,23,31,65,66]. In line with the above -range for accurate angular (pitch & roll) measures are restricted in one or more dimensions Heading will be biased according to the degree of displacement about the z-axis [16] [81] Ensure tag orientation is noted during deployment and retrieval operations (and subsequently used in corrections)…”