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2007 SOUTHEASTERN NATURALIST 6(1):159–164
Testing Tail-mounted Transmitters with
Myocastor coypus (Nutria)
Sergio Merino1, Jacoby Carter1,*, and Garrett Thibodeaux1
Abstract - We developed a tail-mounted radio-transmitter for Myocastor coypus
(nutria) that offers a practical and efficient alternative to collar or implant methods.
The mean retention time was 96 d (range 57–147 d, n = 7), making this a practical
method for short-term studies. The tail-mounts were less injurious to animals than
collars and easier for field researchers to implement than either collars or surgically
Myocastor coypus Molina (nutria) are large semiaquatic rodents endemic
to southern South America that have been introduced around the world as a
furbearer (Carter and Leonard 2002). Methods used to monitor nutria activity
include visual observation, mark-recapture, and radio-telemetry (Evans et al.
1971, Guichon et al. 2003, Lohmeier 1981, Reggiani et al. 1995). Because of
their amphibious nature and susceptibility to dermatitis, the use of radiocollars
is not always practical and often results in morbidity or mortality
(Coreil and Perry 1977, D. Birch, US Fish and Wildlife Service, Blackwater
National Wildlife Refuge, Dorchester County MD, pers. comm.). During an
enclosure study in 2002–03, we monitored nutria using both radio-collars and
implantable transmitters, but found neither satisfactory. When collars were
loose, the animal’s foot could be caught between the collar and the neck,
hindering the animal’s ability to feed and resulting in death (n = 3). Collars
that were too tight dug into the animal’s skin, causing dermatitis, morbidity,
and subsequent death (n = 3; J. Carter, pers. observ.). Surgically implanted
transmitters have been used successfully in Louisiana (Hammond et al. 2003),
but we found this method to be cost prohibitive and logistically challenging.
Considering the limitations of radio-collars and implants, we needed another
short-term practical field method to track nutria movements.
In winter and spring 2003–04, we conducted a study to determine if tailattached
transmitters could be used for short-term studies (2 to 3 months) of
nutria movements and home range.
Our study site was Salvador Wildlife Management Area, located 23 km
southwest of New Orleans in St. Charles Parish, LA (90°20'W, 29°50'N).
The habitat was composed of thin-mat floating marsh (locally called
1USGS National Wetlands Research Center, 700 Cajundome Boulevard, Lafayette,
LA 70506. *Corresponding author - firstname.lastname@example.org.
160 Southeastern Naturalist Vol. 6, No. 1
“flotant”), primarily Type III (Sasser 1994), and open water with submerged
and floating aquatic vegetation. The site was only accessible by airboat or
mudboat. We modified collar transmitters (model M2030, Advanced Telemetry
Systems,Isant; MN, USA) for use as tail-mounted units. Transmitters
were attached onto the exterior of a 5-cm length of 19-mm or 25.4-mm
diameter schedule 40 PVC pipe using a 2-part epoxy (hereafter referred to as
a “unit”). We captured nutria from an airboat using long-handled fishing
nets. The nutria were restrained in a wire squeeze cage. We cleaned tails
with water and disinfected with alcohol. We then slid a unit onto the tail to
determine size and attachment site. The unit was removed and epoxy applied
to the attachment area. We rotated the unit as we slid it over the attachment
area to ensure even distribution of the adhesive inside the pipe. The unit was
held in place for 3 min. We used a “quick set” epoxy glue which bonds in 60
sec. The animal remained in a holding cage for approximately 15 minutes to
cure the epoxy. The nutria was then released within a kilometer of where it
Transmitter status was checked weekly from October 2003 to mid-December
2003, and every 2–3 weeks from mid-December to March 2004. The
transmitters were equipped with a movement-sensitive mortality signal that
doubled the pulse rate after 8 h of inactivity, but were reactivated if the
animal moved again. We determined the detectable ranges of our transmitters
to be 0.5 km if placed at a depth of 15 cm underwater, and between 1–1.5
km if placed at or above the water surface.
When recovering transmitters generating mortality signals, we attempted
to determine the cause. When the unit remained attached to a carcass, we
examined the attachment site for signs of injury. When only transmitters
were recovered, we determined predation by the presence of teeth marks. If a
detached unit was still intact with no chew marks, we presumed that it fell
off the tail. Conical indentations were caused by an Alligator
mississippiensis Dundin 1802 (alligator) attack, and linear marks were presumptive
of chew marks by the incisors of nutria.
Results and Discussion
We determined project status 18 times between October 3, 2003 and March
11, 2004. All 12 deployed transmitters were recovered (Table 1). With few
exceptions, we were able to check the transmitter status once a week for the first
2 months of deployment and thereafter an average of once every 2 weeks. We
were prevented from checking the transmitters some weeks because of logistical
problems, inclement weather, or access restrictions.
All transmitters were recovered within 1.2 km of their initial nutria
release site. Seven of the transmitters fell off, and 5 animals died with their
units attached. We observed 2 animals soon after their units fell off and
noted that their tails were red and raw where the skin sloughed off with the
2007 S. Merino, J. Carter, and G. Thibodeaux 161
unit: significant amounts of hair and skin remained glued to the inside of the
PVC pipe (Fig. 1). Of the 5 mortalities, 3 were designated alligator attacks
Figure 1. Photograph of a nutria tail where the transmitter unit was removed. Note
the missing hair where the unit was attached and some remaining epoxy.
Table 1. Deployment and recovery of radio transmitters.
Date of Retention
Last normal Mortality Transmitter time
Release signal sensor recovered (days)A Cause of mortality signal
03 Oct 2003 27 Jan 2004 19 Feb 2004 19 Feb 2004 118 Mortality- unit still attached to
08 Oct 2003 18 Dec 2003 14 Jan 2004 19 Feb 2004 71 Detached from tail
08 Oct 2003 19 Feb 2004 02 Mar 2004 02 Mar 2004 133 Detached from tail
08 Oct 2003 19 Feb 2004 22 Feb 2004 22 Feb 2004 136 Animal shot by trapper 22 Feb
08 Oct 2003 02 Mar 2004 11 Mar 2004 11 Mar 2004 147 Detached from tail
15 Oct 2003 13 Jan 2004 27 Jan 2004 27 Jan 2004 95 Detached from tail
15 Oct 2003 18 Dec 2003 14 Jan 2004 02 Mar 2004 71 Detached from tail
15 Oct 2003 13 Nov 2003 20 Nov 2003 14 Jan 2004 29 Mortality from alligator
15 Oct 2003 11 Dec 2003 15 Dec 2003 27 Jan 2004 57 Detached from tail
15 Oct 2003 27 Jan 2004 19 Feb 2004 19 Feb 2004 106 Mortality from alligator
21 Oct 2003 11 Dec 2003 15 Dec 2003 02 Mar 2004 57 Detached from tail
21 Oct 2003 28 Oct 2003 29 Oct 2003 29 Oct 2003 7 Mortality from alligator
ARetention time was calculated from the date of release to the date of the last normal signal.
162 Southeastern Naturalist Vol. 6, No. 1
from teeth marks and separation of transmitter from PVC pipe, one died for
unknown reasons, and one animal was taken by a trapper. We examined the
nutria that died for unknown reasons, but found no signs of infection or
tissue damage at the unit attachment site. We were unable to recover any of
the other carcasses for examination.
We calculated retention time for each transmitter by using the most
recent date we found a normal signal (Table 1). Considering only those
animals whose transmitters fell off, the average retention time was 95.9
(± 37.5) days with a range of 57–147 days. All of the whip antennas were
intact, even though they were within reach of the animal (Fig. 2).
To calculate survivorship for the animals used in the study, we treated
the five animals that died as mortalities, and the 7 other animals that dropped
their transmitters were presumed as having survived for the approximately 5
months of the study. The survivorship of 58.3% is within the range of values
reported in the literature, where survivorships as low as 29% to 31% have
been reported (Bounds et al. 2003). However, because we don’t know the
fate of the animals that dropped their transmitters, 58.3% is probably an
overestimate of survivorship.
Several important questions remain unanswered by this study. First, do
the tail-mounted transmitters affect the nutria’s ability to move about and
forage? We think that transmitter units were unlikely to affect movement
because (1) unlike the tails of muskrats or beavers which are flattened, nutria
tails are round in cross section and apparently not adapted to assist in aquatic
Figure 2. Picture of a nutria collected 5 weeks after the transmitter unit was attached.
Note that the antenna is intact and there are no signs of irritation at the site of attachment.
2007 S. Merino, J. Carter, and G. Thibodeaux 163
locomotion, and (2) the nutria’s body form is such that these would not add
significant drag. Second, are there problems associated with skin irritation?
We found 2 animals with skin irritations from the tail-mounted units. The
tails were red and raw where skin sloughed off with the units.
However, the use of tail-mounted transmitters was relatively less stressful
to apply for both the animals and animal handlers. The handling time to
apply tail-mounts is greatly reduced compared to both collars and the
implantation of units and does not require anesthesia. Epoxying of transmitters
has been used on a variety of different animals including birds, fish,
marine mammals, and crocodilians (e.g., Spears et al. 2002). No animals
showed any signs of morbidity associated with the transmitters. We were
unable to ascertain why one animal died, but there were no external indications
that it was the transmitter unit.
For movement studies of short duration, we suggest that tail-mounted
transmitters offer a viable alternative to collars or implants. Tail-mounts are
easier and safer to place on the animals and, in our experience, animals are
less likely to be injured by extended wear of the transmitter. Squeeze cages
are less stressful for the nutria than restraint using a catchpole around the
animal’s neck and shoulder. Benefits to the researchers are reduced handling
time and less risk of being bitten by the animal when working with its tail.
Because sloughing of skin causes detachment of the unit, we do not believe
that a different adhesive would improve retention.
We would like to thank L. Nolfo (Ph.D. Candidate Tulane University, New
Orleans, LA), for her assistance and animal-handling skills. The idea of attaching a
transmitter to a tail was originally suggested to us by Dr. R. Aguilar, Senior Veterinarian
at the Audubon Nature Institute, New Orleans, LA. We would also like to give
special thanks to G. Linscombe (Louisiana Department of Wildlife and Fisheries) for
his continuing support of nutria research and his openness to helping us try new
things. Thanks also to B. Hulslander and W. Adams at the Barataria Unit of Jean
Lafitte National Historical Park and Preserve for their assistance. This project was
supported by funding from the Louisiana Department of Wildlife and Fisheries, the
US Geological Survey (USGS) Invasive Species Program-Nutria Project, and the
USGS/National Park Service National Resources Preservation Program (NRPP).
Thanks again, Greg. This research is covered under the Louisiana Department of
Wildlife and Fisheries Scientific Collecting Permit #LNHP-03-061 and was approved
by the Institutional Animal Care and Use Committee (IACUC) of the USGS
National Wetlands Research Center.
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