Animal lifestyle changes acceptable mass limits for attached tags

Abstract Animal-attached devices have transformed our understanding of vertebrate ecology. To minimize tag-related harm for these studies, researchers have long advocated that tag masses should not exceed 3% of the animal’s body mass. However, this proposition ignores tag forces generated as a result of animal movement. Using data from collar-attached accelerometers on diverse free-ranging terrestrial animals, we detail a tag-based acceleration method (TbAM) in which we quantify animal athleticism in terms of fractions of animal movement time devoted to different collar-recorded accelerations. The varying accelerations are converted to forces imposed on the animals based on the acceleration and tag mass and allow derivation of defined force limits, including those amounting to 3% of the animal’s mass, for specified fractions of any animal’s active time. We demonstrate how species athleticism is the principal determinant of tag forces, whereas body mass is of little importance. Forces exerted by ‘3%’ tags were mostly equivalent to 4-19% of the animals’ masses during moving, with a maximum of 54% in a hunting cheetah. Cumulative frequency curves of tag acceleration for periods when animals were active, all showed a characteristic sigmoid pattern, which was displaced further to the right as higher acceleration activities accounted for an increasing proportion of any animal’s time. Specifying that tags should exert forces that are less than 3% of the animal’s body mass for 95% of the time led to corrected tag masses constituting between 1.6% and 2.98% of our study animals’ masses, with values depending on animal athleticism. Recognition that animal athleticism affects tag forces of their carriers fundamentally changes how acceptable tag mass limits should be determined by ethics bodies. In order to have a scientifically robust acceptable threshold to limit the forces experienced by an animal carrier, we suggest practitioners derive a similar cumulative acceleration profile for their study species and use a minimum of the 95% limits on the plot (although higher limits may be more appropriate).