Evaluating the effects of tracking devices on survival, breeding success, behavior, and condition of a small, partially migratory shorebird

Studies on bird behavior have benefited from the miniaturization of tracking devices and the opportunities for massive data collection facilitated by extensive satellite and cellular infrastructures. However, assessments of the effects of tracking devices on the behavior and survival of birds are rarely conducted and disseminated – raising animal welfare concerns, risking project failure, and hindering optimization of tracking methods within the ornithological community. We quantified the effects of tracking devices on banded dotterels Anarhynchus bicinctus – a threatened, small-bodied (median 59 g), partially migratory shorebird native to New Zealand and a priority for conservation planning on Austral flyways. We deployed ten 1.2-g archival GPS loggers and ten 1.8- to 2-g Argos satellite transmitters on breeding dotterels in Kaikōura, New Zealand. Including leg rings and silicone-tubing leg-loop harness, deployments constituted 2.7–4.3% of an average individual's mass (or 1.9–3.4% for the device alone). Both tracking devices documented the curiously mixed winter strategies characteristic of banded dotterels: migrants flew north to the upper North Island or south to the Canterbury Plains, while other individuals stayed resident in Kaikōura. Compared to a control group of 74 dotterels without tracking devices, neither technology had adverse effects on subsequent breeding outcomes, annual apparent survival, behavior, or body condition, but Argos satellite trackers provided data over a longer period than archival GPS loggers. One possible reason for the absence of adverse effects could be that banded dotterels (and other Charadriinae species) primarily rely on ground-based locomotion, characterized mainly by walking and running – movements that are less hindered by the added mass of auxiliary attachments. Our findings support the ‘3% rule' (i.e. using device weight alone as a guideline), but we suggest that deployment limits of tracking devices could be refined by considering both the species' ability to carry additional weight and its primary mode of locomotion.