Low-cost animal tracking using Bluetooth low energy beacons on a crowd-sourced network

Animal tracking has opened the door to address many fundamental questions in ecology and conservation. While historically animals have been tracked as a means to understand their large-scale movements, such as migration, there is now a greater focus on using tracking to study movements over smaller scales, individual variation in movement, or how movements shape social network structure. With this shift in focus also comes different tracking needs, including the need to track larger numbers of individuals. Tracking studies all face some technological limitations. For example, GPS and other active tracking solutions can collect fine-scale movement data, but have a high cost per tag, limiting the number of individuals that can be followed. They also have high energy costs of data acquisition and download, limiting time periods over which data can be collected. Low-energy passive (e.g. PIT) or active (e.g. reverse GPS) tags can overcome these limitations, but instead require animals to remain within a bounded study area or to come into close proximity to detectors. Here we describe one solution that can overcome many current limitations by employing the massive global network of personal mobile phones as gateways for tracking animals using Bluetooth low energy (BLE) beacons. In areas with medium to high density of people, these simple-to-make beacons can provide regular updates of position over long time periods (battery life 1-3 years). We describe how to use off-the-shelf components to produce BLE beacons that weigh c. 5-6 g and cost < $7USD. Using field testing, we then show that beacons are capable of producing high-frequency tracking data that can be used to build home ranges or to detect spatio-temporal co-occurrences among individuals. BLE beacons are a low cost, low energy solution for studying organisms (e.g. birds, mammals, and reptiles) living and moving in urban landscapes. Their low weight and small size makes them particularly well-suited for tracking smaller species. When combined with fixed gateways, their use can also be extended to non-urban habitats. Their high accessibility is likely to make them an attractive solution for many research projects.