Is abdominal implantation of devices a good alternative to external attachment? A comparative study in Adélie penguins

Abstract

Bio-logging studies suffer from the lack of real controls. However, it is still possible to compare indirect parameters between control and equipped animals to assess the level of global disturbance due to instrumentation. In addition, it is also possible to compare the behaviour of free-ranging animals between individuals equipped with different techniques or instruments to determine the less deleterious approach. We instrumented Adélie Penguins (Pygoscelis adeliae) with internal or external time-depth recorders and monitored them in parallel with a control group during the first foraging trip following instrumentation. Foraging trip duration was significantly longer in the internally-equipped group. This difference was due to a larger number of dives, reflecting a lower foraging ability or a higher food demand, and longer periods of recovery at the surface. These longer recovery periods were likely to be due to a reduced efficiency to ventilate at the surface, probably because the implanted devices pressurised adjacent organs such as air sacs. Moreover, descent and ascent rates were slightly lower in externally-equipped penguins, presumably because external instrumentation increased the bird drag. Looking at our results, implantation appears more disadvantageous-at least for short-term deployment-than external equipment in Adélie Penguins, while this method has been described to induce no negative effects in long-term studies. This underlines the need to control for potential effects due to methodological aspects in any study using data loggers in free-ranging animals, to minimise disturbance and collect reliable data.

Best practice recommendations for the use of fully implanted telemetry devices in pinnipeds

“…Such wires and fixing sutures may increase the likelihood of device effects. Beaulieu et al [32] compared the effects of external (n = 10 animals) and internal (n = 6 animals) tags on the foraging behavior of Adelie penguins. They noted altered foraging behavior in animals carrying internal tags, but none in animals carrying external tags.…”

“…Furthermore, device volume may be more closely related to altered body mass set points in some animals [83], and buoyancy may affect cost of locomotion more than mass [84,85]. Several researchers have suggested that implant size indices based on the percentage device weight in water or volume to body mass ratios should be preferable for aquatic vertebrates [13,17,19,31,32]. Beaulieu et al [32] specifically suggested using device volume per body mass (ml/kg) as a metric.…”

“…Several researchers have suggested that implant size indices based on the percentage device weight in water or volume to body mass ratios should be preferable for aquatic vertebrates [13,17,19,31,32]. Beaulieu et al [32] specifically suggested using device volume per body mass (ml/kg) as a metric. They compared results from their own study to eight other studies on aquatic birds (mostly penguins).…”

Why implantation of bio‐loggers may improve our understanding of how animals cope within their natural environment

“…Finally, because of the invasiveness of surgical implantation and the time required for recovery/healing, which might affect performance, external attachment might be preferable for short-term deployments. For example, Beaulieu et al (2010) found that the dive performance of implanted Adélie penguins (Pygoscelis adeliae) during a single foraging trip (approximately 2 weeks) was significantly reduced when compared with penguins with external device attachment.…”

“…The severity of such a response will depend on the outer material of the implanted device and a surface coating with biocompatible material is, therefore, of great importance, as are proper sterilization procedures (Hawkins 2004;Bryers et al 2012;Mulcahy 2013). Depending on the species in question, device volume might affect body mass set points (Bradley 1978;Adams et al 2001), pressurize adjacent organs such as air sacs in birds (Beaulieu et al 2010), and even interfere with female reproduction (Horning et al 2017), while device mass and buoyancy might affect locomotion costs (Webb et al 1998;Schmidt-Wellenburg et al 2008). In diving species, problems from extensive pressurization might arise, damaging components of the device and, in the worst case, causing battery breakdown and leakage.…”