A review of electronic devices for tracking small and medium migratory shorebirds

Abstract

Small- to medium-sized shorebirds (< 200 g) can be particularly difficult to track with electronic devices due to their small size and long-distance migrations which place restrictions on device weight and size. A lack of comparative information on suitable tracking devices makes selecting the most appropriate technology time consuming and complex and can result in duplication of effort for each research project. The purpose of this paper is to address this issue by presenting a review of the scientific literature and commercially available devices to help inform device selection as well as options for attachment. The ideal device for tracking small to medium migratory shorebirds would be light weight (< 5% of a bird bodyweight), flat in profile, durable, have high battery longevity, remote data download, easy to attach from a bird welfare perspective, high spatiotemporal resolution and would be low in cost (so that a large enough sample size can be obtained). This ideal device does not yet exist due to the limitations on the weight of the power supply necessary to obtain frequent, high resolution location fixes over long time periods. As a result, the current choice of device depends on the purpose of the study. Platform Transmitter Terminal (PTT) doppler devices are suitable for tracking long distance movement due to their smaller size and lighter weight (around 2 g), but produce lower resolution location data and are expensive. For tracking smaller-scale movements (i.e., tens of kilometres), Global Positioning System (GPS) devices are more suitable, because they produce higher-resolution location data and are often more cost effective but tend to be heavier. Other device options for obtaining movement data include radio telemetry and light-level geolocators, which are generally lighter and cheaper than GPS or Doppler devices but require more effort to retrieve data and often produce lower resolution location data. Attachment methods and materials vary, but the most suitable is usually leg loop harnesses made with soft materials that are likely to degrade (e.g., elastic). Device type and harness design need to be carefully chosen to minimize potential impacts on the animal.