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SOUTHEASTERN NATURALIST
2009 8(3):399–410
Nutria Survivorship, Movement Patterns, and Home
Ranges
Lauren E. Nolfo-Clements*
Abstract - Sixteen Myocastor coypus (Nutria) were implanted with radiotransmitters
and monitored on a freshwater fl oating marsh. Mortality and/or transmitter failure
was high, with 5 transmitters failing or being destroyed through predation within 3
days of release. Predation mortality was common, with an additional 5 transmitters
recovered from carcasses within 35 days of implantation. The remaining 6 animals
survived for a mean of 182 days. After removing fi rst movement distances from the
analyses, the mean distance traveled between locations for surviving animals was
77.4 m. Distances varied signifi cantly between seasons, but not between the sexes.
The average minimum convex polygon (MCP) for individuals with suffi cient data
was 28.8 ha and the 95% fi xed kernel (FK) estimates averaged 32.7 ha. There was no
signifi cant difference between home-range estimates overall or between the sexes.
Introduction
Myocastor coypus Molina (Nutria or Coypu) is a large aquatic rodent
endemic to the Patagonian subregion of South America. This mammal has
been transported to various locations around the world as a valued furbearer
(Carter and Leonard 2002). Many of these introduced populations have be-
come established, resulting in the institution of population-control measures
(Bounds and Carowan 2000, Kuhn and Peloquin 1974).
Numerous studies have focused on the movement patterns of the Nutria,
both in its native and introduced range (Doncaster and Micol 1989, Guichon
and Cassini 1999, Reggiani et al. 1993). In the Nutria’s native range, where
these animals are subject to intense hunting pressure, studies are focused
on illustrating the Nutria’s innocuous nature and avoidance of human
settlements (D'Adamo et al. 2000; Guichon and Cassini 1999, 2005). In its
introduced range, studies focus on movement patterns in order to better un-
derstand the Nutria’s overall ecology, either to contribute information to aid
in control efforts (Reggiani et al. 1995) or to enhance means of increasing
harvest effi ciency (Coreil et al. 1988, Ryszkowski 1966).
In Louisiana, where annual Nutria harvests are in the hundreds of thou-
sands and sometimes millions, management efforts focus on controlling
rather then eradicating the population (Scarborough and Mouton 2007).
Despite government funded control efforts, most studies involving Nutria in
Louisiana focus on herbivory and the effects these rodents have on wetland
plant communities (Evers et al. 1998, Ford and Grace 1998, Gough and
*Department of Ecology and Evolutionary Biology, Tulane University, 400 Boggs
Center, New Orleans, LA 70118; Current address - Department of Biology, Suffolk
University, 41 Temple Street Boston, MA 02114; lnolfo-clements@suffolk.edu.
Southeastern Naturalist Vol. 8, No. 3
400
Grace 1998, Randall and Foote 2005, Taylor and Grace 1995). Few studies
in Louisiana have focused on the movement patterns and activities of the
Nutria (Coreil et al. 1988, Warkentin 1968).
The purpose of this study was to uncover seasonal and sex-specifi c
trends in Nutria home ranges and movement patterns. I examined Nutria
home ranges and movements both annually and seasonally. This study was
conducted in a freshwater fl oating marsh in southeastern Louisiana. To the
author's knowledge, no other examination of Nutria movement patterns has
been conducted in this type of environment.
Field-site Description
This study was conducted in the Barataria Unit of Jean Lafi tte National
Historical Park and Preserve (JLNHPP), located about 24 km south of New
Orleans in Jefferson Parish, LA. Wetland habitats comprised about 4900 ha
of the total park area of approximately 7500 ha (D.P. Muth, JLNHPP, pers.
comm.). The climate was subtropical with annual rainfall exceeding 160 cm
and mean annual temperature of 21°C (summer average of 28.5 °C, winter
average of 12.2 °C). The growing season typically exceeded 260 days. The
study site was at or slightly below sea level (White et al. 1983).
The wetland habitats of the JLNHPP included fl oating marsh, spoil banks,
and open water habitats. The fl oating-marsh habitat roughly coincided with
types 1–5 thick-and thin-mat fresh fl oating marsh, as characterized by Sasser
et al. (1994). This habitat was nearly devoid of woody vegetation except
for patches of Morella cerifera (L.) Small (Myrica cerifera; Wax Myrtle)
distributed across the marsh. Canals that were dug primarily for oil and gas
exploration in the 1940s–70s provided access to the marsh.
These canals were lined by spoil banks that were constructed from the
sediments excavated in the digging of the canals. Woody vegetation domi-
nated this habitat type, in contrast to the herbaceous species that dominated
the surrounding canal and marsh communities. Smaller bodies of water that
traversed open expanses of marsh are referred to as trenasses, French-Acadi-
an for “trail on the marsh.” Trappers probably dug these waterways as routes
for laying trap lines (D.P. Muth, pers. comm.). Trenasses averaged 2–3 m
wide and were usually completely covered with fl oating aquatic vegetation
during the growing season.
For a full description of the wetland habitats of JLNHPP, including a
species checklist, see Nolfo-Clements (2006). Voucher specimens from that
plant survey are housed at the Tulane University Herbarium.
Methods
Radiotelemetry
Sixteen adult Nutria (8 females, 8 males) were captured off of an airboat
and implanted with radiotransmitters (Nolfo and Hammond 2006) during
January 2004 (7 animals), December 2004 (2 animals), and January 2005
L.E. Nolfo-Clements2009 401
(7 animals). Animals were released within 24 hours of surgery at a location
in the marsh within 100 m from their point of capture, with one exception.
All animals were located at least 2 and no more than 4 times per week using
a 3-element Yagi antenna attached to a LA12-Q receiver (AVM Instrument
Company, Colfax, CA). Relocations occurred at this interval to avoid auto-
correlation of data points (Swihart and Slade 1985).
All transportation to the marsh areas of JLNHPP was done in a 14-foot
aluminum fl atboat with a 70-horsepower outboard motor within the canals
of the Park. Marsh travel was done on foot. All radiolocations were done
on foot or from a canoe. Either visual or auditory (movement in brush or
splashing) confi rmation of an animal’s presence was required to confi rm a
location. A GPS point was taken at each locality using a Garmin Etrex Ven-
ture handheld GPS receiver (Forestry Suppliers, Jackson, MS).
Statistical analyses
I plotted all Nutria locations on a 1998 digital orthophoto quarter quad-
rangle (DOQQ) of the study area downloaded from the Louisiana statewide
GIS site (www.atlas.lsu.edu) and projected into ArcView GIS, Version 3.2.
1999 from ESRI (Environmental Systems Research Institute, Inc., Redlands,
CA). I calculated successive movement distances, minimum convex polygon
(MCP), and fi xed kernel (FK) estimates with 95, 50, and 25% contours us-
ing the animal movements extension for ArcView version 1.1 (Hooge and
Eichenlaub 1997). There were insuffi cient data to calculate seasonal MCPs
and FK estimates.
I calculated successive movement distances and survivorship for all ani-
mals. I calculated the MCP and FK estimates only for animals that survived
>60 days and therefore had ≥15 radiolocations. I chose the FK estimate ver-
sus the adaptive kernel estimate of home range for these analyses because,
although adaptive kernel may give the most accurate picture of actual home
range, FK produces the least-biased estimates of home-range area with the
lowest error, which is especially important when dealing with low sample
sizes (Seaman and Powell 1996, Seaman et al. 1999, Worton 1989).
I compared survivorship to mean distance traveled for all animals using
correlation analysis and tested for linear relationships using Pearson’s cor-
relation coeffi cient and linear regression analysis. I did the same between
the sexes and for survivorship versus MCP areas and FK 95% contour areas.
I used a combined ANOVA to examine the interactions between season, sex,
and distance traveled. I then compared distances traveled between seasons
and between the sexes using an ANOVA with Tukey’s pairwise comparison.
Due to the distance between capture and release sites, all distance analy-
ses were conducted both with and without the fi rst distance traveled included
in the analyses. In seasonal analyses, winter was December–February, spring
was March–May, summer was June–August, and fall was September–No-
vember. All statistical analyses were performed using the Paleontological
Statistics Software Package for Education and Data Analysis (PAST) (Ham-
mer et al. 2001). I used P < 0.05 to identify signifi cant differences.
Southeastern Naturalist Vol. 8, No. 3
402
Results
I collected 249 radiolocations over the course of the study (146 for males,
96 for females). Five of the implanted animals had either transmitter destruc-
tion or total transmitter failure within 3 days of release and did not yield any
data. The remaining 11 animals survived a mean of 105 days (range = 5–486
days) and traveled a mean of 91.2 m (range = 1.4–1931.3 m) between reloca-
tions (Fig. 1). However, once the fi rst distance traveled between release and
fi rst relocation was removed from the analysis, the mean distance traveled
dropped to 77.4 m. There was no correlation between survivorship and mean
distance traveled.
The removal of the fi rst distances traveled measurements only affected
the mean distance moved for the winter since that was when all captures and
implantations took place. Nevertheless, even with the fi rst distances trav-
eled data removed, the mean distances traveled varied signifi cantly between
seasons, with the distances being highest in the winter (mean =113.7.0 m,
SE = 21.1 m), lowest in the summer (mean = 35.9 m, SE = 5.6 m), and inter-
mediate in the spring (mean = 72.7 m, SE = 14.6 m) and fall (mean = 54.7 m,
SE = 10.3 m) (Fig. 2). There was no signifi cant difference between distances
traveled between the sexes overall or seasonally, nor were there any interac-
tions between distance traveled, sex, and season.
Only 6 Nutria (3 males and 3 females) survived for >60 days and there-
fore accumulated ≥15 relocations per individual. The survivorship for these
animals was a mean of 182 days. Their mean MCP home-range area was 28.8
ha. Their mean FK estimate contours at 95, 50, and 25% respectively were
32.7, 6.0, and 2.4 ha, respectively (Table 1). There was no statistical differ-
ence between MCP or 95% FK areas between the sexes. There was some
overlap in both MCP and FK home ranges (Fig. 3).
Figure 1. Survivorship in days versus mean distance traveled for male and female
Nutria monitored at JLNHPP 2004–2005.
L.E. Nolfo-Clements2009 403
Discussion
Survivorship
The low survivorship of the Nutria was not completely unexpected. Due
to the size of the transmitters used, animals had to weigh at least 4 kg in
order to be implanted (Nolfo and Hammond 2006). Any animal that did not
meet this criterion was released upon initial capture. We estimated Nutria
of this weight to be approximately 7–9 months of age following Louisiana
Nutria growth curves created by Atwood (1950). Although there are records
of captive Nutria surviving up to 6 years (Gosling and Baker 1982), data
suggests that up to 80% of Nutria in the wild die in their fi rst year (Willner
et al. 1983) and that individuals over 3 years of age rarely constitute >15% of
a wild population (Guichon et al. 2003b). Because the animals in this study
were at least 7 month old, they would probably have succumbed to natural
mortality within months even without the implantation.
Additionally, although Nolfo and Hammond (2006) recommended that
Nutria be held in a predator-free environment for at least 72 hours before
release, this was not feasible for this study. Therefore, the high initial mortal-
ity may be attributed in part to a protracted recovery time or disorientation
Figure 2. Mean distance traveled by season for Nutria monitored at JLNHPP ± 1
SE (n = 78, 108, 37, and 17 for winter, spring, summer, and fall, respectively). First
distances traveled after release are omitted from the analysis. Means do not statically
differ between the sexes and are therefore combined for each season.
Table 1. Sex, identifi cation number (#), survivorship, number of locations, MCP area, and 95%
FK area of Nutria monitored at JLNHPP 2004–2005.
Sex (#) Survivorship (days) # of locations MCP (ha) 95% FK (ha)
Male ( n16) 61 15 23.9 66.8
Female (n5) 80 17 54.2 54.6
Male (n10) 126 32 28.7 16.3
Female(n14) 126 33 9.0 8.3
Female (n7) 212 39 47.1 43.7
Male (n2) 486 97 10.1 6.5
Southeastern Naturalist Vol. 8, No. 3
404
after release. Another factor that must be considered in the high mortality of
the Nutria in this study is the density of predators at the study site. Both Al-
ligator mississippiensis Daudin (American Alligator) and Canis latrans Say
(Coyote) are very abundant (L.E. Nolfo-Clements, unpubl. data), and Nutria
have been reported to fall victim to these predators at other locations (Kinler
et al. 1987, Valentine et al. 1972).
Movement patterns
The seasonal differences in distances traveled recorded in this study co-
incide with previous results for Louisiana Nutria, but not for Nutria in other
parts of the world. Coreil et al. (1988) found that female Nutria in Louisiana
maintained much larger home ranges in the winter then in the summer. In
contrast Reggiani et al. (1993) and Doncaster and Micol (1989) found that
Nutria did not show any seasonal changes in movement patterns in Italy
and France.
The lack of statistical difference detected in male versus female move-
ment patterns in this study contrasts the findings of previous studies and
may be due to small sample size. Gosling and Baker (1989) and Doncaster
and Micol (1989) found that male Nutria moved further than females be-
tween radiolocations.
One of the main reasons for some of the discrepancies in the fi ndings
between this study and other Nutria movement studies may be the length
Figure 3. 95, 50, and 25% FK contours for male and female Nutria labeled by indi-
vidual. Male 95% areas are dark, female areas are light. Release points are marked
with stars “★.”
L.E. Nolfo-Clements2009 405
of time between radiolocations. In previous studies, animals were relocated
at set time intervals within a 24-hour period (i.e., every 30 minutes; Coreil
et al. 1988, Edwards et al. 2001, Foerster and Vaughan 2002, Gosling and
Baker 1989, Linders et al. 2004). These studies aimed at pinpointing the
length of daily movement or assessing diel patterns of activity. My goal
was to assess the long-term movement patterns of the Nutria; therefore,
radiolocations were made less frequently, similar to other seasonal move-
ment assessments (Chamberlain and Leopold 2005, Diffendorfer et al. 2005,
Kamler et al. 2005, Roth 2005).
A factor that may have contributed to a few of the longer distances
traveled, especially by the male n10, was the distance between the point of
capture and the point of release. However, even after removing the fi rst dis-
tances traveled by animals upon release, these animals still exhibited notably
long travel distances for this species. All animals except n10 were released
within approximately 100 m of their capture site from a centralized location.
Animal n10 was released over 1 km from his capture site due to extremely
low water levels on his release date that did not allow for his transport to
his capture locale. N10 was released at the same point as n14 and n16, but
it is clear that he promptly traveled directly back to his area of capture and
established his home range in that area (Fig. 3). Although this may have
artifi cially infl ated n10’s MCP home range, it did not have any effect on his
95% FK home range (Table 1).
Home range
Although other studies have assessed Nutria home ranges using MCP,
this is the fi rst study that utilized FK estimates. Past studies on Nutria home
ranges have all occurred on introduced populations. There have been no
home-range or movement studies conducted in their native South American
range. In all of the studies that evaluated both sexes, male Nutria were re-
ported to have larger home ranges then females.
In an observational and mark-recapture study of an enclosed, breed-
ing, population of Nutria in Poland, Ryszkowski (1966) found that females
tended to have more restricted (smaller) home ranges then males. In Italy,
Reggianni et al. (1993) reported signifi cant differences in home-range sizes
between radio-collared males and females in the spring but not in the winter.
They found that the average home-range area across both seasons and both
sites was 5.27 ha for females and 14.90 ha for males.
Gosling and Baker (1989) used a combination of mark-recapture and
radiotelemetry to evaluate the movements and ranging behaviors of Nutria
in Great Britain prior to their eradication. They found that males had signifi -
cantly larger home ranges than females at all sites. Additionally, the size of
these home ranges varied signifi cantly between sites. In areas with patchy
resource distribution and low population densities, the average home-range
size was 93.9 ha for males and 46.3 ha for females. In contrast, in an area
where resources were more evenly distributed and population densities were
higher, the average was 6.8 ha for males and 3.0 ha for females.
Southeastern Naturalist Vol. 8, No. 3
406
In a marsh in central west France, Doncaster and Micol (1989) used
radiotelemetry to assess the home ranges of male and female Nutria. They
found that males had larger home ranges than females and traveled along
greater lengths of the canal in the study site then did the females (average
home range of 5.68 ha for males and 2.47 ha for females).
In Mississippi, Lohmeier (1981) conducted a radiotelemetry-based study
on Nutria and found the mean home range for these animals was 2.31 ha.
Using MCP, Denena et al. (2003) found that Nutria inhabiting a reservoir/
recreation area in Texas had a mean home range of 2.7 ha (1.6 ha for females
and 3.6 ha for males).
In Louisiana, there have been two previous studies that have specifi cally
examined movement patterns of Nutria. Warkentin (1968) used a combina-
tion of mark-recapture and visual observations to uncover the behaviors and
movements of Nutria in and around man-made ponds adjacent to WWII mu-
nitions bunkers. She observed that the majority of those animals remained
within approximately 274 m (300 yards) of their original capture site. Coreil
et al. (1988) radio-tracked female Nutria in an intermediate marsh habitat.
They found that animals had the largest MCP home ranges in the winter (138
ha) and the smallest in the summer (7.2 ha).
In comparison to these studies on other introduced Nutria populations,
the mean annual MCP and 95% FK ranges for the animals in this study are
relatively large (28.8 and 32.7 ha, respectively). This result may be due to one
of two factors: 1) the pooling of seasonal data; as observed by Coreil et al.
(1988), Nutria in Louisiana appear to have signifi cantly larger home ranges in
the winter than in the summer. The combination of data from all seasons due
to small sample sizes may therefore have translated these seasonal differences
into larger annual averages. 2) Patchy resource distribution and/or low popu-
lation densities at this site (see discussion above; Gosling and Baker 1989).
Another possible explanation for the large home ranges found in this
study may be the small sample sizes utilized in the analyses. Although MCP
estimates necessarily increase as the sample size increases (White and Garrott
1990:151), the opposite is true of FK, estimates where a smaller sample size
sometimes leads to infl ated contour areas (Seaman et al. 1999). This discrep-
ancy is only apparent for one animal is this study. Male n16, who survived for
61 days and had 15 relocations, had a MCP home range that was noticeably
smaller then his 95% FK area (Table 1). Overall, the MCP and 95% FK areas
found in this study did not statistically differ, and therefore their compara-
tively large extents are probably not due to insuffi cient relocation sample
sizes. However, the small number of animals used in these analyses (6) calls
into question the utility of extrapolating these results to other populations,
especially in other wetland habitat types.
A noteworthy aspect of these home ranges is the similarity in mean ar-
eas for males and females. Nutria have been reported as gregarious in areas
of both their native and introduced range with groups usually consisting of
multiple females, their young, and a single male (Doncaster and Micol 1989,
L.E. Nolfo-Clements2009 407
Gosling and Baker 1989, Guichon et al. 2003a). Others have concluded that
Nutria were territorial, with a defi nite dominance hierarchy (Reggiani et al.
1993, Ryszkowski 1966, Warkentin 1968). Most home-range and movement
studies report larger home ranges for males, with a single male’s range over-
lapping that of one or more females (Doncastor and Micol 1989, Guichon et
al. 2003a, Reggiani et al. 1993).
This study did reveal some home-range overlap. This fi nding may be due
to shared release sites, but could also be due to social interactions between
radio-implanted individuals (Fig. 3). For example, the male n16 and female
n14 were radio-located together on 2 occasions. The overlap between male
n2 and female n7 was due to their utilization of communal burrows below a
canal spoil bank, although they were never radio-located simultaneously in
this area. There was also home-range overlap of the females n5 and n7, who
were located within 75 m of each other on 3 occasions.
As stated, this is the fi rst study to examine the movement patterns of
Nutria on a freshwater fl oating marsh, which, as its name indicates, is not
attached to a substrate for most if not all of the year. The variability in fl oat-
ing marsh mat thickness has been noted by Sasser et al. (1994, 1996). These
different mat thicknesses are associated with whole suites of vegetative char-
acteristics (Nolfo-Clements 2006). It has also been documented that Nutria
utilize areas of different mat thicknesses and plant species composition on
a seasonal basis (Nolfo-Clements, in press). Hence, the variability in fl oat-
ing marsh habitat adds another dimension to habitat selection and movement
patterns for this species; that of mat thickness. I have even witnessed Nutria
burrowing through the mat, swimming beneath it, and reappearing in a nearby
trenasse or canal, a feat that would prove impossible in an attached marsh.
Conclusions
This study of the movement patterns and home ranges of Nutria on a
fl oating marsh revealed useful information regarding both methodologies
and results. Based upon the relatively high mortality and low survivorship of
the majority of radio-implanted Nutria, future radiotelemetry studies on this
species should focus on short-term movement patterns with more frequent
relocations and/or a greater number of radio-implanted animals.
Although the home ranges calculated for these animals were larger then av-
erage when compared with other Nutria studies, this fi nding may be attributed
to the nature of the unique habitat under consideration, the possibility of patchy
resource distribution, and the pooling of seasonal data. This study revealed a
small glimpse of the ranging behaviors of Nutria on a freshwater fl oating marsh,
one that could be greatly expanded through further study and observation.
Acknowledgments
I would like to thank the staff of Jean Lafi tte National Historical Park and Pre-
serve. A special thanks to N. Walters, who was instrumental to the completion of this
project, for GIS assistance and Nutria capture. Thanks to L. Zahm and W. Adams for
boat use, maintenance, and fi eld support. Thanks to C.S. Hood for all of his guidance,
Southeastern Naturalist Vol. 8, No. 3
408
support, and editorial comments. Thanks are also extended to the Maryland Coopera-
tive Fish and Wildlife Research Unit for the loan of radiotransmitters. This research
was funded by grants from the National Parks Service and the Coypu Foundation.
This project was covered under Tulane University Institutional Animal Care and Use
Committee protocol # 0230-3-16-082.
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