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

Abstract

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.