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

We review long-term patterns of tracking device use and the reporting of the effects of such devices on individual birds. We assessed > 3400 primary references including > 1500 containing information as to whether effects were looked for and reported. Numbers of papers published increased at 4.4% yr(-1). Research on foraging and energetics focussed on seabirds while work on habitat use and dispersal was focussed mainly on landbirds. Migration was the most common study topic overall and increased markedly from the turn of the century in all three bird groups. The proportion of studies reporting effects of devices on individuals declined at > 1% yr(-1), while the proportion of studies providing no information on effects increased by ca 0.7% yr(-1). The presence of a control group increased the likelihood of a study reporting effects, (45 vs 33%). We modelled the probability of reporting effects separately for three bird groups and two attachment durations. Occurrence of effects was significantly related to attachment method (4 models), year (4 models) and relative device mass (1 model). Invasive attachment methods were associated with a high incidence of effects while tail and leg attachments showed relatively few effects. Probabilities of reporting effects declined over time and increased with relative device mass, however there was no device mass threshold below which effects were not observed. Approaches designed to minimize potential effects of devices on individual birds and to improve scientific rigour have advanced substantially. Nevertheless ca 55% of studies contained no information on potential effects and in many more documentation was inadequate. We call for more systematic documentation of potential effects in peer-reviewed publications to support more rigorous science and to further improve bird welfare.