Social Behavior and Group Formation in the Coypu (Myocastor coypus) in the Argentinean Pampas

Abstract

This study presents the first description of social behavior and structure in native populations of the coypu (Myocastor coypus). Data from behavioral observations and trapping were used to describe group composition and behavior at 3 study areas in east-central Argentina in 1999–2000. Seven groups were described (11 coypus/group ±1.5 SE). Groups were characterized by several adult and subadult females, 1 dominant male, several adult and subadult males, and a variable number of juveniles. Subgroups (mainly composed of juveniles and small adult males) were also identified within some groups. Group fidelity was relatively high. Amicable interactions and cooperative behaviors such as nursing in groups, allogrooming, and alarm calls occurred within groups. Agonistic interactions and marking behavior were rare but suggested that the largest male was socially dominant. This study confirms gregarious habits and a polygynous mating system for the species and provides the first report of the existence of some cooperative behaviors.

Full text

254
Journal of Mammalogy, 84(1):254–262, 2003
SOCIAL BEHAVIOR AND GROUP FORMATION IN THE COYPU
(MYOCASTOR COYPUS) IN THE ARGENTINEAN PAMPAS
M. L
AURA
G
UICHO
´N
,* M
ARIELA
B
ORGNIA
,C
ARINA
F
ERNA
´NDEZ
R
IGHI
,G
UILLERMO
H. C
ASSINI
,
AND
M
ARCELO
H. C
ASSINI
Departamento de Ciencias Ba´sicas, Universidad Nacional de Luja´n, Rutas 5 y 7, (6700) Luja´n,
Buenos Aires, Argentina
This study presents the first description of social behavior and structure in native popula-
tions of the coypu (Myocastor coypus). Data from behavioral observations and trapping
were used to describe group composition and behavior at 3 study areas in east-central
Argentina in 1999–2000. Seven groups were described (11 coypus/group
6
1.5 SE). Groups
were characterized by several adult and subadult females, 1 dominant male, several adult
and subadult males, and a variable number of juveniles. Subgroups (mainly composed of
juveniles and small adult males) were also identified within some groups. Group fidelity
was relatively high. Amicable interactions and cooperative behaviors such as nursing in
groups, allogrooming, and alarm calls occurred within groups. Agonistic interactions and
marking behavior were rare but suggested that the largest male was socially dominant. This
study confirms gregarious habits and a polygynous mating system for the species and
provides the first report of the existence of some cooperative behaviors.
Key words: behavior, coypu, Myocastor coypus, nutria, social structure
The coypu or nutria (Myocastor coypus)
is a herbivorous rodent that inhabits banks
of rivers, lakes, lagoons, marshes, and
swamps (Gosling and Baker 1991). This
semiaquatic rodent is indigenous to the
southern half of South America but was in-
troduced into several areas around the
world early in the 20th century, including
North America, Europe, the Middle East,
Africa, and Japan (Gosling and Baker
1991). Population dynamics and regulation
(Doncaster and Micol 1989, 1990; Gosling
et al. 1981; Reggiani et al. 1995) and re-
production (Gosling 1981, 1986; Gosling
and Baker 1991; Newson 1966; Willner et
al. 1979) have been intensively studied only
in a few feral populations. Females can
breed throughout the year, give birth to 5–
6 young after a gestation period of 4
months, and nurse for 8 weeks. Weight at
birth is about 0.2 kg; individuals reach
* Correspondent: lalifer@vianw.com.ar
maximal body size of approximately 6 kg
by 2 years of age (Gosling and Baker
1991).
Social organization of the species is
poorly known (Jouventin et al. 1996). The
most complete studies describe a polygy-
nous mating system, with a matriarchal or-
ganization composed of groups of related
females (Gosling and Baker 1989; Gosling
and Wright 1994). However, other authors
report no gregarious habits (Reggiani et al.
1993; Ryszkowski 1966) or different types
of gregariousness (Ashbrook 1948; Ehrlich
1966; Warkentin 1968). The objective of
this study was to provide the 1st description
of social behavior and structure of wild
coypu populations in native habitat.
M
ATERIALS
A
ND
M
ETHODS
Study area.—The work was conducted at 3
study sites in the Province of Buenos Aires, east-
central Argentina. Grassland steppe was the
original dominant habitat in this area, but it has
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February 2003 GUICHO
´N ET AL.—SOCIALITY IN COYPUS 255
T
ABLE
1.—Observation of coypus in Argentina, showing duration and dates of observation and
trapping sessions (number of days and month(s) when observation or trapping was conducted), num-
ber of trap-nights, number of coypus caught, and range of body mass of individuals captured. The
number of coypus caught also includes a few individuals that were observed during observation
sessions but that were not captured.
Site Season Observation
sessions Trapping
sessions Trap-
nights Coypus
caught Body mass
(kg)
Ruiz Spring 1999
Summer 2000
Autumn 2000
Winter 2000
4 days, Feb.
4 days, Apr.
16 days, Aug.–Sep.
8 days, Oct.
10 days, Jan.
7 days, Apr.
8 days, Jul.
472
650
441
464
47
50
43
42
0.3–5.9
0.5–5.5
1.1–5.1
0.5–5.5
Luja´n Spring 1999
Summer 2000
Autumn 2000
Winter 2000
7 days, Nov.–Dec. 4 days, Nov.
4 days, Mar.
5 days, Jun.
4 days, Sep.
128
124
170
136
7
4
6
5
2.5–4.4
1.2–4.4
1.9–4.7
2.2–4.6
Ja´uregui Spring 1999
Summer 2000
Autumn 2000
Winter 2000
7 days, Sep.–Dec.
15 days, Dec.–Mar. 7 days, Nov.
9 days, Feb.
11 days, May
4 days, Aug.
329
387
396
168
35
44
36
25
0.2–6.2
0.8–5.8
0.5–6.2
0.7–5.6
been widely modified due to livestock and ag-
ricultural practices and urbanization (Cabrera
1971). The climate is temperate (mean temper-
ature 9.1
8
C in winter and 23.8
8
C in summer),
with mean annual rainfall of 944 mm (Goldberg
et al. 1995). During our study, total precipitation
in spring and summer (355 mm) was consider-
ably less than the mean total rainfall for the
same period in 1989–1999 (649 mm). The total
precipitation in the autumn of our study (544
mm) was nearly twice as high as that recorded
for the autumn of 1989–1999 (246 mm). Thus,
during our study a drought occurred in summer
and a flood in autumn.
The 1st study site (Ruiz; 34
8
12
9
S, 59
8
16
9
W)
was a 1.5-km-long portion of stream that crosses
3 fields with natural grasslands (i.e., nonsown
pastures) used for raising cattle. The 2nd site
(Luja´n; 34
8
35
9
S, 59
8
04
9
W) was formed by 2
small ponds (0.6 and 0.08 ha) separated by a
portion of stream about 100 m long. These
ponds were located in fields with natural pas-
tures used for cattle grazing on the campus of
the University of Luja´n, Buenos Aires, Argen-
tina. The 3rd site (Ja´uregui; 34
8
35
9
S, 59
8
11
9
W)
was a pond (4.3 ha) in a large field. This pond
had been constructed for recreational purposes
in 1960 by modifying a natural watercourse but
was rarely used for this purpose during the
study. It contained 3 small islands (45 by 40, 90
by 20, and 45 by 20 m), the water was covered
by Lemna, which was widely present and evenly
distributed, and the dominant vegetation around
the pond consisted of grasses and planted trees.
Data collection.—Coypus were live-trapped
seasonally from spring 1999 to winter 2000 at
the 3 study sites (19 days of preliminary trap-
ping were conducted between summer and win-
ter 1999). During trapping sessions (Table 1) we
attempted to capture most coypus present in the
area; trapping was concluded when recaptures
exceeded 80% of total captures for 2 consecu-
tive days. Cage traps (80 by 25 by 25 cm) were
placed at burrow openings or on paths or for-
aging sites near them; traps were baited with ap-
ple before sunset and checked and closed before
sunrise. Animals were not transported; they were
marked and released in their trapping location.
Coypus were immobilized by intramuscular in-
jection of a combination of ketamine hydrochlo-
ride (4 mg/kg) and xylazine hydrochloride (0.5
mg/kg—Bo´ et al. 1994). Body mass and repro-
ductive condition were recorded for all coypus.
Assessment of sexual maturity was made for
males on the basis of whether or not the penis
was completely eversible and for females on the
basis of whether or not the vulva was perforate
(Gosling et al. 1981). Coypus were classified as
juveniles (sexually immature individuals) and
subadults or adults (sexually mature coypus
weighing
,
3kgor
.
3 kg, respectively). Juve-
niles weighing
,
1.5 kg were considered to be
offspring born between trapping sessions. A to-
tal of 87 individuals (40 males, 40 females, and
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256 Vol. 84, No. 1JOURNAL OF MAMMALOGY
6 nontrapped juveniles) was trapped at Ruiz, 14
(8 males, 6 females) at Luja´n, and 55 (23 males,
32 females) at Ja´uregui.
Two types of marks were used for visualiden-
tification: ear tags and hair dye. A combination
of ear tags of different colors and shapes al-
lowed individual identification. For complemen-
tary identification the hair was cut on 1 area
(about 4 by 3 cm) on the head or back and the
dense underfur was dyed with black hair dye
sold commercially for human use. The dye was
dry in 30 min (approximately the time that an-
imals remained anesthetized).
Behavioral observations were conducted from
spring 1999 to winter 2000 (Table 1). Most be-
havioral sampling was in spring at Luja´n, sum-
mer at Ja´uregui, and winter at Ruiz. We ob-
served animals for 280 h on 59 days using a
telescope (60
3
) and binoculars (12
3
50) during
the evening and a monocular light intensifier
with an infrared illuminator during the night.
Video recording was also done during both day
and night. At Ruiz, feeding trays were placed
near burrow entrances to facilitate individual
identification on the video. Scan sampling at 15-
min intervals was alternated with focal obser-
vation during these intervals at Ja´uregui and
Ruiz (Martin and Bateson 1993). At Luja´n only
focal sampling was conducted.
During scan sampling, activity of each indi-
vidual was recorded: foraging, grooming, inter-
acting with another individual, in alert position,
resting, or locomotion (swimming or walking—
D’Adamo et al. 2000; Gosling 1979; Warkentin
1968). At Ja´uregui, location of each individual
in every scan was also recorded on a 10 by 10
m grid (marked with stakes). Activity of coypus
was registered in 305 scans; the number of coy-
pus in each scan varied from 1 to 36.
During focal sampling, coypus using (entering
or emerging from) each burrow were identified,
and social behavior was recorded. Three types
of amicable interactions were recorded: body
contact (foraging or self-grooming with bodies
in contact), naso-nasal greetings (approaching or
making contact with the noses), and allogroom-
ing. One type of agonistic interaction was re-
corded: aggression (expelling the subdued ani-
mal from a place). Except for allogrooming, the
other categories have been described previously
(Ehrlich 1966; Gosling and Baker 1991; Rysz-
kowski 1966; Warkentin 1968).
Location of all burrow openings was mapped
at each site. Previous description of burrows
showed that they can have 1–2 openings or,
more commonly, 5–7 openings over a distance
of approximately 5 m (Laurie 1946; Sierra de
Soriano 1963; Warkentin 1968). The 193 burrow
openings facing the water at the 3 sites were
distributed nonrandomly (goodness-of-fit to a
Poisson distribution, P
,
0.05); approximately
80% of these burrows were
,
5 m from one an-
other. Based on these and previous results(open-
ings within 5 m distance belong to the same
‘‘den’’—Warkentin 1968), burrow clusters were
defined as groups of openings separated by
,
5
m from one another. Twenty-two clusters were
found at Ruiz; 22 at Ja´uregui; and 2 at Luja´n.
Mean number of openings in each cluster was
4.5
6
0.2 SE (n
5
46, range 1–17); clusters ex-
tended from 0.3 to 25 m of shoreline. Nests (de-
scribed by Ehrlich 1966; Laurie 1946; Rysz-
kowski 1966; Sierra de Soriano 1963) were ob-
served at Ruiz in winter.
Data analysis.—A group was defined as a set
of individuals that used 1 cluster of burrows (de-
termined through direct observations of animals
entering or emerging from burrows) or shared
exclusive use of an area (determined through di-
rect observation or trapping). Coypus that used
the same cluster of burrows were assigned to the
same social group. Trapping data were used to
define group composition if capture locations
showed high overlap among individuals, spatial
segregation of groups, and groups of individuals
equivalent to the group composition that resulted
from observational data when both types of data
were available. For the latter analysis a corre-
lation coefficient for dichotomous nominal-scale
data (r
n
, range
2
1to
1
1—Zar 1996) was cal-
culated between location of trapping site and the
location of the cluster of burrows used for in-
dividual coypus. This coefficient was obtained
for all animals that were both captured and ob-
served in summer, autumn, and winter at Ruiz.
At Luja´n no statistical method was applied to
validate trapping data because only 1 group was
identified. At Ja´uregui no spatial segregation
among individuals was detected from trapping
data, and only observational data were used to
identify group composition in summer. There-
fore, group composition was described through-
out the year at Ruiz and Luja´n (i.e., 4 group
configurations) and only in summer at Ja´uregui
(i.e., 1 group configuration).
Subgroups were identified within a group
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February 2003 GUICHO
´N ET AL.—SOCIALITY IN COYPUS 257
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ABLE
2.—Composition of the groups and subgroups of coypus at 3 study sites in Argentina.
Ruiz site
Group 1
Main Subgroup Group
2Group
3Group
4
Luja´n site
Group 1
Main Subgroup
Ja´uregui site
Group
1
Group 2
Main Subgroup
1Subgroup
2
Spring 1999
Juvenile
Subadult female
Subadult male
Female
Male
15
6
4
1
1
1
2
2
2
10
2
1
1
2
1
1
1
1
Summer 2000
Juvenile
Subadult female
Subadult male
Female
Male
8
2
4
6
1
1
1
1
4
2
1
1
1
12
1
3
1
1
1
11
8
1
1
6
1
a
1
5
2
a
7
1
1
3
Autumn 2000
Juvenile
Subadult female
Subadult male
Female
Male
5
1
3
3
1
1
1
1
1
6
1
2
7
2
2
4
1
2
2
11
Winter 2000
Juvenile
Subadult female
Subadult male
Female
Male
1
5
32
2
1
1
2
2
1
10
5
1
5
2
2
1
11
a
The same individual was the largest adult male of both groups.
based on observational data. These subgroups
comprised individuals that used a burrow cluster
adjacent to the main one and used the main clus-
ter only occasionally and were not chased out;
they foraged and moved together with the mem-
bers of the main group. In these cases, a group
comprised a main group and 1 or a few sub-
groups.
At Ja´uregui, the standardized Morisita index
of dispersion (I
p
, range
2
1to
1
1—Krebs 1989)
was calculated to analyze the pattern of coypu
distribution in summer. The locations of individ-
uals on the 10-m grid recorded during scan ses-
sions (1 scan/day with at least 8 animals) at
Ja´uregui were used. Data are presented as mean
6
SE.
R
ESULTS
Group composition.—We identified 7 so-
cial groups at the 3 study sites, averaging
11
6
1.5 coypus/group (range 3–25; Table
2). Mean group composition was 5
6
1 ju-
veniles, 0.9
6
0.3 subadult females, 3
6
0.4
females, 0.6
6
0.2 subadult males, and 1.9
6
0.3 adult males. Three groups (1 at each
study site) had subgroups (Table 2). Fifty-
three percent of animals belonging to a sub-
group were juveniles, and 32% were rela-
tively small adult males (body mass
,
4 kg).
Fourteen of 15 group configurations that
had
.
1 sexually mature male contained a
full-grown male (4.6
6
0.2 kg) that was
significantly larger than the other mature
males of the group (X
¯,3.3 kg
6
0.1; Wil-
coxon paired-sample test: n
5
14, P
,
0.001).
A description of the results obtained at
each study site follows. At Ruiz, 4 groups
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258 Vol. 84, No. 1JOURNAL OF MAMMALOGY
were identified (Table 2) because they used
different burrow clusters. Members of 1
group using a burrow cluster never used the
cluster of another group and used a second-
ary cluster only occasionally (8% of 322
recordings). The distribution of capture lo-
cations revealed that these groups used 4
contiguous areas (Fig. 1). The limits of
these 4 areas remained constant throughout
the year. Individual locations were signifi-
cantly correlated for all individuals (in sum-
mer: r
n
5
0.93 for 21 individuals; in au-
tumn: r
n
5
0.8 for 9 individuals; in winter:
r
n
5
1 for 22 individuals; P
,
0.001).
A subgroup within group Ruiz-1 (2 adult
males of body mass 3.2 and 3.3 kg) used a
burrow cluster about 8 m from the group’s
main cluster in winter (Table 2). Subgroups
in other seasons may not have been detect-
ed due to insufficient data.
Few movements of individuals between
social groups were recorded at Ruiz: 85%
of 20 mature females and 78% of 18 mature
males remained in the same social group
throughout the study period, whether or not
they were sexually mature at 1st capture.
Most individuals that changed group mem-
bership between seasons were 2–3 kg in
body mass for females (55% of 11 cases)
or 3–4 kg for males (46% of 13 cases).
At Luja´n, direct observations and capture
locations revealed 1 group that contained 1
subgroup (Table 2). Each of the 2 ponds
had only 1 burrow cluster; the main group
was settled on the largest pond, and the sub-
group occupied the small pond. Three of
the 3–6 members of the main group re-
mained in the group for most of the study
period (11 months).
At Ja´uregui, 2 groups were identified
(Table 2) because they used 2 burrow clus-
ters located on 2 different islands and used
a secondary cluster only occasionally (12%
of 477 recordings). The largest male of the
population (5.8 kg) used both clusters; each
group also had smaller males (2.9–3.7 kg).
Two subgroups were identified within
group Ja´uregui-2 (Table 2).
Behavioral observations.—Foraging was
the major activity (87% of 2,111 recordings
from scan sampling), followed by swim-
ming or walking (6%), vigilance (4%),
grooming (2%), and interacting with others
(1%). Coypus were never observed
.
10 m
from water at either Ruiz or Ja´uregui. In
summer at Ja´uregui, animals were rarely
observed
.
10 m from coastline into the
water (6% of 1774 recordings) and were ag-
gregated when observed outside the bur-
rows (I
p
.
0.5, P
,
0.05).
Thirty-two of 46 aggressive interactions
occurred at burrow entrances and seemed to
be related to burrow defense. The ratio of
aggressive behaviors sent to behaviors re-
ceived was 14:0 for the largest adult male
of the group, 16:6 for adult females, 3:2 for
other adult males, and 2:11 for subadults
and juveniles.
A total of 102 amicable interactions was
recorded. Adult females, subadults and ju-
veniles, and adult males were involved in
65, 52, and 13 of these interactions, respec-
tively. The largest male interacted amicably
only with adult females (n
5
11), and in-
dividuals of the other categories interacted
among themselves.
We also observed categories of behavior
that have not been described before for this
species (nursing in groups, allogrooming,
marking over other coypus, and alarm call-
ing). Up to 6 adult and subadult females
and at least 5 recently born coypus were
observed resting with their bodies in con-
tact on a nest composed of sedges (Scir-
pus). The 2 largest females (4.2–4.9 kg)
were nursing the 5 recently born, suckling
coypus. The offspring walked over the
backs of all females, occasionally stopping
and moving their noses through the pelage
in the region of the dorsolaterally placed
mammary glands, as if they were searching
for teats. There were no aggressive respons-
es from any of the females to these apparent
suckling attempts. The 2nd category of be-
havior described is allogrooming (n
5
4)
by a small adult male or an adult female
consisting of using the mouth to clean the
back and face of another animal (all adult
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February 2003 GUICHO
´N ET AL.—SOCIALITY IN COYPUS 259
F
IG
. 1.—Composition of social groups as shown by capture sites of coypus in trapping sessions
during 4 seasons at Ruiz, Argentina. Trapping data showing high overlap among individuals and
spatial segregation of groups was used to define group composition. Coypus were captured along a
stream (gray line at left) at burrow clusters (black rectangles on streamline) at and near the main
burrow cluster (gray circles) identified for each portion of the stream. The number (n) of individual
coypus captured in each season and capture locations are shown by circles (males, filled circles;
females, open circles). Vertical lines joining circles indicate the individuals that were captured at
$
2
burrow clusters. Area of circles is proportional to percentage of captures of each individual in each
cluster. The 4 social groups of coypus and the area used by each group are indicated on the right.
No trapping was conducted on the last 200 m of stream in spring.
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260 Vol. 84, No. 1JOURNAL OF MAMMALOGY
females); this behavior was observed at
burrow entrances. Self-grooming in groups
of 2–3 individuals (n
5
13) with their bod-
ies in contact or very close to each other
was also observed. The 3rd category of be-
havior was indulged in by the largest male
at Ja´uregui, which urinated on burrow en-
trances in the main cluster and also urinated
on a small adult male that approached him
when he was at a burrow entrance with an
adult female. Finally, an alarm call was ob-
served 3 times on 2 different days. It was
given by an adult female while she swam
in circles in front of her burrow. Calling
seemed to be elicited by the presence of
dogs, lasted 2–5 min, and was composed of
repeated, high-pitched humming sounds,
each about 1–2 s in duration.
D
ISCUSSION
We found that coypus live in territorial
groups typically composed of several adult
and subadult females, 1 dominant male,
several adult and subadult males, and a var-
iable number of juveniles. These results
agree with previous studies on feral popu-
lations, which found that the species is gre-
garious (Ashbrook 1948; Ehrlich 1966;
Warkentin 1968), polygynous (Doncaster
and Micol 1989; Gosling and Baker 1989),
and territorial (Gosling and Wright 1994).
However, Reggiani et al. (1993) and
Ryszkowski (1966) reported no gregarious
habits for this species. The former study
found no clear evidence of gregariousness
based on radiotracking, a result likely due
to insufficient information. Ryszkowski
(1966) reported solitary habits for adult
coypus inhabiting enclosed marshes in
crowded conditions based on observations
and trapping data. He concluded that coy-
pus had no ‘‘herd’’ relationships, based on
social tolerance observed between animals
provided with supplemental food in captiv-
ity. Ryszkowski (1966) also concluded that
territorial behavior was absent because cap-
ture locations were randomly distributed.
However, his methods may not have been
sufficiently reliable to detect such behavior.
Our observations suggest the existence of
both dominance and cooperation in the so-
cial behavior of coypus in their natural en-
vironment. The largest males of the groups
were the aggressors in agonistic encounters,
and they scent-marked both burrow en-
trances and other coypus. This behavioral
pattern suggested that they were socially
dominant over other members of the groups
and could be important in the maintenance
of spatial segregation among groups (Gos-
ling and Wright 1994).
Evidence of cooperative behavior was
foraging in groups, nursing in groups, al-
logrooming, and alarm calls. Most of this
evidence is preliminary but is the 1st de-
scription for the species. Future research on
these types of cooperative behaviors is de-
sirable because it will contribute to the un-
derstanding of the evolution of group-living
mammals.
We observed that movements between
social groups occurred mainly at interme-
diate ages, suggesting that dominant indi-
viduals were tolerant to smaller adult males
and females but may have excluded them
from groups as they grew larger.
A wide range of social and mating sys-
tems has been described in hystricomorph
rodents, including monogamy, polygyny,
and promiscuity (Branch et al. 1993; Her-
rera and Macdonald 1987; Redford and Ei-
senberg 1992; Rood 1972; Taber and Mac-
donald 1992). Several attempts have been
made to link this variability with ecological
factors in order to understand the evolution
of sociality of hystricomorphs (Ebensperger
and Cofre´ 2001; Lacher 1981; Sachser
1998). Results of these studies are limited
by the paucity of information for many spe-
cies. However, information now available
about social behavior of coypus places
them among the most social of these rodent
species. At least 2 other species share sim-
ilar characteristics regarding social structure
and behavior: vizcachas (Lagostomus max-
imus—Branch et al. 1993) and capybaras
(Hydrochoerus hydrochaeris—Herrera and
Macdonald 1987, 1989). High sociality and
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February 2003 GUICHO
´N ET AL.—SOCIALITY IN COYPUS 261
the combination of dominant and coopera-
tive behaviors described in this study sug-
gest that coypus constitute an interesting bi-
ological model to study the evolution of so-
cial systems.
R
ESUMEN
Este estudio presenta la primera descrip-
cio´n del comportamiento y de la estructura
social de poblaciones de coipos (Myocastor
coypus)ensua´rea de distribucio´n original.
Se utilizaron datos provenientes de obser-
vaciones de comportamiento y de captura
viva de coipos para describir la composi-
cio´n de los grupos y el comportamiento de
los individuos en tres sitios de estudio ubi-
cados en la Regio´n Pampeana, Argentina
durante 1999–2000. Se describieron siete
grupos (11 coipos/grupo
6
1.5 SE). Los
grupos estaban formados por varias hem-
bras adultas y sub-adultas, un macho domi-
nante, pocos machos adultos y sub-adultos
yunnu´mero variable de juveniles. Tambie´n
se identificaron subgrupos (principalmente
formados por juveniles y machos adultos
pequen˜os) dentro de algunos grupos. La fi-
delidad de los individuos a su grupo fue
relativamente alta. Se observaron interac-
ciones amistosas y de cooperacio´n entre in-
dividuos de un mismo grupo, como por
ejemplo amamantamiento en grupos, aci-
calamiento entre individuos y llamados de
alarma. Las interacciones agresivas y las
conductas de marcado fueron escasas pero
sugirieron que el macho de mayor taman˜o
era dominante sobre los dema´s. Este estudio
confirma que los coipos tienen ha´bitos gre-
garios y un sistema de apareamiento poli-
gı´nico y provee la primera descripcio´n de
algunos comportamientos cooperativos que
no habı´an sido observados en esta especie.
A
CKNOWLEDGMENTS
P. Arnedillo, M. Bello, V. Benı´tez, A. Bianchi,
M. Cristiano, L. Fasola, C. Sagario, and P.Stam-
pella collaborated in trapping sessions. M. Kevy
and I. Sterverlynck kindly allowed us to conduct
this work on their properties. A. Guicho´n com-
mented on a previous version of this work. F.
Milesi offered important assistance during field-
work, revision of the manuscript, and prepara-
tion of the figure. L. M. Gosling and an anon-
ymous referee provided helpful criticism on an
earlier version of the manuscript. M. L. Guicho´n
was supported by a grant from the Comisio´n de
Investigaciones Cientı´ficas, Province of Buenos
Aires, and Fundacio´n Antorchas. M. H. Cassini
was supported by a grant from the Consejo Na-
cional de Investigaciones Cientı´ficas y Te´cnicas.
Universidad Nacional de Luja´n and Organiza-
cio´n Profauna funded this project.
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Submitted 21 January 2002. Accepted 7 July 2002.
Associate Editor was Edward H. Miller.
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