A comparison of use of tail-mount and collar attachment methods for nutria (Myocastor coypus) telemetry

Background/Question/Methods

Background: The traditional method of attaching telemetry devices to nutria (Myocastor coypus) is with a collar around the neck. However, several researchers have noted that seasonal changes in weight often cause fatal problems with collar fit in nutria. To address this some have proposed the use of collars made of a material designed to degrade to allow the collar to detach before seasonal weight change problems can occur. An alternative method is to glue the transmitter to a small section of PVC pipe. The nutria's tail is then threaded through the pipe and glued with epoxy. Eventually the pipe section and transmitter sloughs off the tail.

Question: Which method of transmitter attachment (tail or collar) is better?

Methods: We compared the tail-mount with a collar designed to fall off after 90 days. The same model of transmitter was used with both attachment methods.  Nutria were randomly assigned to treatment and the two groups did not significantly differ with respect to weight or sex. During attachment, animals fitted with the tail-mounts (n = 16) were restrained without anesthesia in a squeeze cage, while animals fitted with collars (n = 14) were anesthetized. This study was conducted in four urban wetlands near Portland, Oregon, USA.

Results/Conclusions

Overall mortality was 29.6% (similar to other nutria telemetry studies). Mortality was significantly higher with collars (54.5%) than with tail-mounts (12.5%). Smaller nutria had higher mortality with collars than with tail-mounts. For example, small nutria (2.0 kg, n=3) with collars died, but a 1.5 kg nutria had a successful tail-mount deployment and transmitter recovery. Average transmitter retention time was not significantly different. Transmitter detachment rates were 47.5% for collars and 87.5% for tail-mounts. Two animals with tail-mounted transmitters lost their tails and attached transmitters. One of these tailless individuals was spotted several times afterwards but the long-term fate of either animal is unknown.

The breakaway design for the collars needs improvement, and individuals capable of short-term rapid weight change (juveniles and pregnant females) may not be good candidates for collars. The tail-mount technique might be improved by the use of different glue that would be less irritating to the skin and improved sizing of the sections of PVC pipe to prevent tail loss. Tail-mounts are a viable, and less expensive alternative to collars that work on a wider range of nutria sizes and may be useful for other species.