Using radio‐frequency identification technology to monitor Eurasian Beavers

The use of radio-frequency identification (RFID) offers new potential in remote wildlife monitoring to reduce the invasive nature of studies requiring direct contact with study animals. Facilitated by the emergence of new technology, RFID can remotely identify individual animals implanted with passive-integrated-transponder (PIT) tags. We aimed to establish and assess a new technique for remote RFID for remotely and noninvasively monitoring a wild population of a semi-aquatic mammal, the Eurasian beaver (Castor fiber). A fixed reader was installed from June 2018 to July 2019 at beaver lodges within the territories of 8 family-groups in Vestfold and Telemark, Norway, for 3 nights per lodge, with RFID antennas at lodge entrances. Microchipped beavers were detected when entering or leaving the lodge. The family-group size recorded using RFID was compared to the known family-group size based on live capture records and direct observations. The family-group size recorded using RFID was smaller than the known family-group size. However, testing suggested that individuals inhabiting a lodge with a fixed reader installed had a high probability of detection (98.44%). Fixed readers are effective where the identification of individuals at a focal point is appropriate, with unique applications for monitoring species with high fidelity to lodges or dens, or species that exhibit central-place foraging behavior. Research using RFID through fixed PIT tag readers should be given priority for noninvasive beaver population monitoring. Whereas fixed PIT tag readers may not record entire beaver family-groups, they provide an accurate and efficient alternative to other monitoring techniques. (c) 2021 The Authors. Wildlife Society Bulletin published by Wiley Periodicals LLC on behalf of The Wildlife Society

Retention and Loss of PIT Tags and Implanted VHFs and Bio-Loggers in the Eurasian Beaver

Abstract Background Passive integrated transponder devices (PIT tags) are a valuable tool for individual identification of animals. Similarly, the surgical implantation of transmitters and bio-loggers can provide useful data on animal location, physiology and behavior. However, to avoid unnecessary recapture and related stress of study animals, PIT tags and bio-loggers should function reliably for long periods of time. Here, we evaluated the retention of PIT tags, and of very high frequency (VHF) transmitters and bio-loggers that were either implanted subcutaneously or into the peritoneal cavity of Eurasian beavers (Castor fiber). Results Over a 21-year period, we implanted PIT tags in 456 individuals and failed to detect a PIT tag in 30 cases, consisting of 26 individuals (6% of individuals). In all instances, we were still able to identify the individual due to the presence of unique ear tag numbers and tail scars. Moreover, we implanted 6 VHFs, 36 body temperature loggers and 21 heart rate loggers in 28 individuals, and experienced frequent loss of temperature loggers (at least 6 of 23 recaptured beavers) and heart rate loggers (10 of 18 recaptured beavers). No VHFs were lost in 2 recaptured beavers. Conclusions Possible causes for PIT tag loss (or non-detection) were incorrect implantation, migration of the tag within the body, a foreign body reaction leading to ejection, or malfunctioning of the tag. We speculate that logger loss was related to a foreign body reaction, and that loggers were either rejected through the incision wound or, in the case of temperature loggers, possibly adhered and encapsulated to intestines, and then engulfed by the gastro-intestinal tract and ejected. We discuss animal welfare implications and give recommendations for future studies implanting bio-loggers into wildlife.</jats:p

Retention and loss of PIT tags and surgically implanted devices in the Eurasian beaver

Abstract Background Passive integrated transponder devices (PIT tags) are a valuable tool for individual identification of animals. Similarly, the surgical implantation of transmitters and bio-loggers can provide useful data on animal location, physiology and behavior. However, to avoid unnecessary recapture and related stress of study animals, PIT tags and bio-loggers should function reliably for long periods of time. Here, we evaluated the retention of PIT tags, and of very high frequency (VHF) transmitters and bio-loggers that were either implanted subcutaneously or into the peritoneal cavity of Eurasian beavers (Castor fiber). Results Over a 21-year period, we implanted PIT tags in 456 individuals and failed to detect a PIT tag at recapture in 30 cases, consisting of 26 individuals (6% of individuals). In all instances, we were still able to identify the individual due to the presence of unique ear tag numbers and tail scars. Moreover, we implanted 6 VHFs, 36 body temperature loggers and 21 heart rate loggers in 28 individuals, and experienced frequent loss of temperature loggers (at least 6 of 23 recaptured beavers) and heart rate loggers (10 of 18 recaptured beavers). No VHFs were lost in 2 recaptured beavers. Conclusions Possible causes for PIT tag loss (or non-detection) were incorrect implantation, migration of the tag within the body, a foreign body reaction leading to ejection, or malfunctioning of the tag. We speculate that logger loss was related to a foreign body reaction, and that loggers were either rejected through the incision wound or, in the case of temperature loggers, possibly adhered and encapsulated to intestines, and then engulfed by the gastro-intestinal tract and ejected. We discuss animal welfare implications and give recommendations for future studies implanting bio-loggers into wildlife. </jats:sec

Additional file 1 of Retention and loss of PIT tags and surgically implanted devices in the Eurasian beaver

Additional file 1: Table S1. Overview of all body temperature loggers implanted to Eurasian beavers (Castor fiber), showing the beaver ID, sex, temperature logger model, and fate of the logger. Table S2. Overview of all heart rate loggers implanted to Eurasian beavers (Castor fiber), showing the beaver ID, sex, heart rate logger model, and fate of the logger. Table S3. Estimate, standard error (SE), lower (LCI) and upper (UCI) 95% confidence interval, and P-values of explanatory variables for the full model analyzing the probability of PIT tag loss in a given year. Female sex and the age class ‘>3 year old’ were used as reference level. Note that the intercept only model was the highest-ranking model based on AIC. Table S4. Estimate, standard error (SE), lower (LCI) and upper 95% confidence interval (UCI), and P-values of explanatory variables for the full model analyzing the probability of (1) temperature logger loss and (2) heart rate logger loss. Female sex, temperature logger type ‘Centi-T’, and heart rate logger type ‘RVL-LINQ‘ were used as reference level. Note that the intercept only model was the highest-ranking model based on AIC