Effects of tracking devices on individual birds – a review of the evidence

Tagged Cuckoo, photograph by Chris Hewson

Author(s): Geen G.R., Robinson R.A., Baillie S.R.

Published: January 2019

Journal: Journal of Avian Biology

Digital Identifier No. (DOI): 10.1111/jav.01823

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Newly-published work by BTO has reviewed the long-term patterns in the use of tracking devices on individual birds, and how the effects of the use of such devices are reported. More than 3,400 peer-reviewed publications were included in this review. The numbers of papers based on tracking studies increased by 4.4% per year between 1962, when this technology was first deployed, and the end of 2017. The types of ecological questions addressed with tracking devices varied between groups of species. For example, seabirds have mostly been tracked for studies on foraging and energetics, while landbirds have primarily been tracked to investigate habitat use and dispersal. Migration was the most common study topic across all species.

The review showed that the proportion of studies reporting the effects of tracking devices on birds has declined. Devices can significantly impact tagged individuals in many ways, including reducing survival and reproductive success. The proportion of studies reporting effects of devices on individuals fell by > 1% per year, while the proportion of studies providing no information on effects increased by ca. 0.7% per year. The presence of a control group increased the likelihood of a study reporting effects, (45% vs 33%). 

The work found that the occurrence of effects was significantly related to attachment; invasive methods were associated with a high incidence of effects while tail and leg attachments showed relatively few effects. Probabilities of reporting effects have declined since the tracking began, as practice has improved, and adverse effects were more likely with heavier devices relative to a bird’s mass. Although methods have improved substantially, 55% of studies contained no information on potential effects and in many more documentation was inadequate. This work highlights the continuing need for more systematic documentation of potential effects in peer-reviewed publications, to support more rigorous science and to further improve bird welfare.

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