Miniaturization of biologgers is not alleviating the 5% rule

Abstract

The use of biologging technology has increased exponentially over the last decade, allowing us to study animal behaviour at a level of detail not previously possible. It is clear from recent meta‐analyses that the attachment of such devices can have negative effects on individual animals, particularly their behaviour and physiology. In recognition of this, a commonly applied rule is to ensure that devices borne by flying animals weigh less than 5% of their body mass. Over time, the continuing miniaturization of devices should facilitate the deployment of devices that are an ever‐decreasing fraction of animal mass. Despite these considerations regarding device mass, here we show that there has been no apparent reduction in the relationship between body mass and the mass of logging devices over the last 48 years. Using a meta‐analytical approach, we demonstrate that the ongoing miniaturization of animal‐borne devices has resulted not in a decrease in the relative device mass borne by animals, but instead has prompted researchers to measure smaller and smaller species. We recommend that researchers better exploit the ongoing miniaturization of devices to reduce the relative mass of the devices borne by animals, and avoid blind adoption of the 5% or any other arbitrary rule when designing research programs.

Minimizing the impact of biologging devices: Using computational fluid dynamics for optimizing tag design and positioning

“…On the contrary, our results suggest that there may be scope to increase the size of tags, within reason, providing that their form ultimately leads to a reduction in drag (Figure ) – see also Shorter et al () and Fiore et al (). Certainly, seen in this light, the persistent stated aim to simply ‘miniaturize' biologging devices may be too simplistic (Portugal & White, ).…”

“…Indeed, researchers often select their study animals based on the size or weight requirements for the tags, rather than trying to optimize tags for a given species or size class, although there are examples of specific developments made for very small animals (Stidsholt et al, 2018). Despite this, most studies using tags have so far largely failed to take advantage of technological advancements to reduce the impact of tags on animals (Portugal & White, 2018). Crucially, for projects involving tags on aerial and aquatic animals, the focus on weight by most existing tag guidelines -for example the 3% or 5% rule (Casper, 2009) -ignores aero/hydrodynamic impacts (most notably drag) which are key in modulating energy expenditure and behaviour during swimming (Cornick, Inglis, Willis, & Horning, 2006;Culik & Wilson, 1991;Rosen, Gerlinsky, & Trites, 2017;van der Hoop et al, 2018) and flight (Bowlin et al, 2010;Pennycuick, Fast, Ballerstädt, & Rattenborg, 2012; but see Tomotani, Bil, Jeugd, Pieters, & Muijres, 2019).…”

Impacts of “supermoon” events on the physiology of a wild bird

“…The temperature sensor of the encapsulated data logger was calibrated by immersing the device in water baths of known temperature. The mass of the internally implanted device (21 g) was comfortably below the 5% of total body mass recommended when deploying internally implanted biologging devices on birds (Portugal & White, 2018;White et al, 2013). Mean daily heart rate of all geese was used to determine daily activity levels (see Portugal, Green, White, Guillemette, & Butler, 2012), in order to identify the autumn migratory flights taking place in September, from Svalbard to Scotland.…”

The neglected impact of tracking devices on terrestrial arthropods

“…These effects can be partially mitigated, for instance by the mode of attachment (White et al, ) and by minimizing tag size (Bodey et al, ; Casper, ). However, as tracking devices are becoming lighter and smaller, they are increasingly used on smaller animals (Portugal & White, ). As researchers are pushing the boundaries of the size at which species are presumed ‘taggable’, the impact of the device on the animal's performance is not necessarily reduced.…”

“…These effects can be partially mitigated, for instance by the mode of attachment (White et al, 2013) and by minimizing tag size (Bodey et al, 2017;Casper, 2009). However, as tracking devices are becoming lighter and smaller, they are increasingly used on smaller animals (Portugal & White, 2018).…”