FIELD TECHNIQUES
Free-ranging platypuses have been monitored using eDNA, live capture-release studies, radio-telemetry, data loggers, remote observational studies, camera traps and acoustic transmitters (Grant 2009; Gust and Griffiths 2010; Griffiths et al.
2013; Bino et al. 2018). Each of these methods has limitations: live capture studies are very labour intensive and often have low recapture rates; radio-telemetry and data loggers are limited by battery life, problems associated with application of the device and difficulties of recapture for device retrieval; and camera traps, observational studies and public surveys do not enable individuals to be identified (Macgregor et al. 2014). A recent study demonstrated that the use of consolidated time-lapse camera imagery can effectively be used to detect and monitor platypus activity (Roberts and Serena 2024). Intraperitoneal implanted acoustic transmitters have been used effectively in platypuses, using an array of acoustic sensors to track movements (Bino et al. 2018; see Chapter 10). This allowed investigation of detailed fine- and large-scale movements and habitat use; however, the technique is invasive and labour-intensive, requiring surgical implantation and the deployment and retrieval of multiple sensors from river systems.Macgregor et al. (2014) investigated the novel use of instream microchip readers to remotely monitor the movements of microchipped wild platypuses. They demonstrated that at appropriate sites, in-stream microchip readers are an effective method of monitoring the movements and survival of microchipped free-ranging platypuses.
The current standard method of body condition assessment in platypuses is the tail volume index (TVI) (Booth and Connolly 2008). Macgregor et al. (2016) assessed performance of the TVI and developed and evaluated the performance of new techniques for routine field assessment of platypus body condition. Three new indices were developed: relative tail fat volume (RTFVTBl) based on cross-sectional area measurements from ultrasound images compared with total body length; and two body condition indices intended for routine field use: one based on body mass and bill width (body condition index: BCIBW) and the other based on a single linear ultrasonographic measurement of tail fat depth and bill width (relative fat depth: RFDBW). Results indicated that RFDBW outperforms TVI as an index of platypus tail fat, but further work is needed to determine the relationship between tail fat and total body fat before any conclusions can be drawn (Macgregor et al. 2016). In practical terms, TVI still remains a useful and commonly used tool to gauge body condition in platypuses.