Tracking Without Harm?
A field-test of mini GPS and satellite devices on New Zealand’s threatened Banded Dotterels finds that small tracking devices can be safely used without measurable impacts on behaviour, breeding, or survival – offering reassurance for shorebird conservation and telemetry efforts
Testing the technology on a conservation priority
Banded Dotterels (Anarhynchus bicinctus) are a partially migratory shorebird endemic to New Zealand and listed as ‘Declining’. Understanding their varied migratory strategies is crucial for conservation, and remote tracking technologies offer powerful tools to achieve this. However, concerns remain about potential negative impacts of devices on small-bodied birds.
Researchers from the Max Planck Institute and New Zealand’s Department of Conservation deployed two types of tracking devices – 1.2-g archival GPS loggers and 1.8–2-g Argos satellite transmitters – on 20 adult Banded Dotterels at Kaikoura. Including harness and leg rings, the total attachment weight reached up to 4.3% of body mass, slightly exceeding the widely adopted ‘3% rule’ for small flying birds.
To determine whether such deployments affect fitness or behaviour, the researchers compared tracked birds with a control group of 74 individuals, following them over three breeding seasons.
No measurable impact on fitness or breeding success
The study found no significant effects of either tracking technology on key metrics. Apparent survival rates were similar across all groups – control, GPS-tagged, and PTT-tagged – averaging around 81–83%. Likewise, no clear differences emerged in nest fate or the likelihood of fledging young. While there was a slight, non-significant trend toward more nest abandonment among PTT-tagged birds, sample sizes were small.
Repeated body condition measurements showed that tracked birds maintained similar scaled mass indices compared to controls, even across seasons. Behavioural observations also found no differences in walking, feeding, incubating, or flying – and no abnormal behaviour was noted in birds wearing devices.
Short migrations, long data sets
Tracking confirmed the expected diversity in winter strategies among Kaikoura dotterels. Some individuals migrated north to the upper North Island, others south to the Canterbury Plains, while several remained resident. Notably, none of the tracked birds undertook trans-oceanic migration.
The satellite PTTs outperformed the GPS loggers in data quantity, yielding over 5,500 location fixes compared to just over 100 from GPS tags. They also lasted longer – averaging 44.5 weeks of coverage versus 27 weeks for the GPS units – and several reactivated after winter, while GPS tags did not.
However, device loss due to harness failure was recorded in both groups, and solar charging efficiency declined in autumn, especially for resident birds. These practical limitations suggest areas for further improvement in deployment design and power efficiency.
Ground birds, grounded conclusions
A key insight from the study is that the primary locomotion mode of a species may mediate its tolerance for tracking devices. Banded Dotterels are largely terrestrial, engaging mostly in walking and running, with flight used infrequently outside of migration. This may explain their apparent tolerance of tracking loads slightly exceeding 3% of body weight.
The authors recommend that deployment thresholds should not rely on rigid rules alone but instead consider species-specific behaviour and ecology. A ‘one-size-fits-all’ mass limit may unnecessarily restrict valuable research on species like the Banded Dotterel.
Calls for transparency and cautious optimism
The researchers emphasise the importance of publishing pilot studies like this one. Too often, results from device trials go unpublished, hindering collective progress and leading to duplicated efforts or avoidable welfare concerns.
While this study suggests that modern miniature tracking devices can be safely used on small, ground-based migratory shorebirds, the authors caution that long-term effects beyond one annual cycle remain unknown. Devices did detach after months, indicating that harness design can act as a safety valve – but continued vigilance is needed, especially for longer-term deployments or in more aerial species.
For now, this study offers robust, field-based evidence that miniaturised telemetry devices can help unlock the mysteries of partial migration without harming their tiny wearers.
Why this study matters
Long-term datasets from tropical regions are rare, making this century-spanning study especially valuable. The subtle but measurable changes in body shape and size serve as indicators of broader ecological shifts and highlight the importance of continued monitoring. The study calls for further investigation into the mechanisms behind these changes, combining ecological, behavioural, and physiological research to fully understand how tropical birds - and biodiversity more generally - are coping with a warming world.
July 2025
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