An open-source sensor-logger for recording vertical movement in free-living organisms

Measuring individual-based movements in free-ranging animals is relevant to our understanding of many basic ecological principles (migration, competition, optimal foraging) but has been difficult to realize in a small size. We have developed a freely available, open-source, non-invasive datalogger that can measure an animal's altitude or elevation (A) at sampling intervals greater than once per second, storing up to 10,000 total samples, depending on programme size. The realized design weighs 370mg, opening a wealth of opportunities to study animals as small as 10g without exceeding the 4% rule-of-thumb for the relative mass of telemetry devices. In addition, power management is provided via a modern ultra-low-power microcontroller, making it possible to record altitude data over extended periods (>100days) by extending battery lifetimes. First results from testing and field applications of this design underline its suitability for reliable and extended monitoring of how animals interact with the environment. Our empirical results show this design can provide high-resolution data with altitude measurements accurate to the nearest several metres at 1-s intervals, provided a local known elevation pressure reference, elucidating fine-scale differences between species/individuals in their use of the air column over 10-day intervals.