Male-male ritual combat in Spilotes pullatus (Serpentes: Colubrinae)

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INTRODUCTION
Some males snakes present morphological
changes during reproduction in the breeding
season and also display social interactions, such
as male-male ritual combat. Ritual combat
involves the interaction between two males,
apparently in competition for mating dominance
(Carpenter, 1977). Generally, the ritual consists
of bodily contact between males. They exert
pressure, either by pushing or twisting one
another, with the goal being to physically
dominate an opponent by forcing their head
toward the ground (Carpenter, 1977).
Combat between males has been described
for several snake taxa; Boidae, Elapidae,
Viperidae and Colubridae (Carpenter, 1977;
Shine, 1978, 1994; Almeida-Santos & Marques,
2002). Different taxa exhibit different behaviour
during a ritual. During combat colubrids tend to
assume a horizontal posture with trunk and tail
regions entwined and some oblique or slight
vertical elevation of the head (Carpenter, 1977).
Combat is usually observed during the breeding
season (Capula & Luiselli, 1997; Schuett, 1997;
Schuett et al., 2001) and factors such as body
size of the male and previous combat experience
are important for victory in combat and mating
success (Schuett, 1997).
The genus Spilotes (Wagler, 1830)
(Colubridae, Colubrinae) comprises one
species, Spilotes pullatus. It is a widely
distributed snake, inhabiting areas of Central
and South America from Tamaulipas in Mexico
to Paraguay, and across the extreme northeast
of Argentina (Savage, 2002). It is a diurnal,
terrestrial and arboreal (Vanzolini et al., 1980;
Sazima & Haddad, 1992; Marques, 1998; Boos,
2001; Marques & Sazima, 2004; Pontes &
Rocha 2008).
METHODS
The description of ritual combat by S. pullatus
herein was based on footage and detailed notes
from four observations. The four instances
detailed combat in situ in Brazil. Ritual combat
#1 and #2 were observed in the southeast
region, on Cardoso Island in the municipality of
Cananéia, state of São Paulo (25° 7’S 47°
57’W) in early spring. Ritual combat #3 and #4
were observed in the central-west region of
Brazil in late spring and early summer
respectively. Combat #3 was filmed on the left
bank of Sucuriú River (19º 08’ 30”S 52º 58’
03”W), Paraiso Farm, municipality of Costa
Rica, state of Mato Grosso do Sul and combat
#4 was filmed at Vagafogo Farm (15º 50’
14.62”S 48º 58’ 33.35”W), municipality of
Pirenópolis, state of Goias (Table 1).
RESULTS
Description of the ritual
Males of S. pullatus kept their bodies partially
entwined during combat (Fig. 1). The intensity
at which the bodies became entwined varied.
Specimens tried to keep the cranial portion of
the body in the most upright position, trying to
raise their heads as far as possible above the
ground (Fig. 1a and 1d). The male that was
disadvantaged in rituals retreated its head,
loosened its body from the entwined posture,
25© 2013 British Herpetological Society
Short Note
Male-male ritual combat in Spilotes pullatus
(Serpentes: Colubrinae)
DIEGO FERREIRA MUNIZ-DA-SILVA1,2* and SELMA MARIA ALMEIDA-SANTOS1
1Laboratório de Ecologia e Evolução, Instituto Butantan,
Av. Vital Brazil, 1500, 05503-900 São Paulo, SP, Brazil
2Setor de Anatomia, Departamento de Cirurgia, Faculdade de Medicina Veterinária e Zootecnia,
Universidade de São Paulo, Av. Orlando Marques de Paiva 87,
05508 270 Cidade Universitária/São Paulo, SP, Brazil.
*Corresponding author e-mail: diegomuniz.vet@gmail.com
Herpetological Bullen (2013) 126: 25-29

and placed its body back to a vertical position
by raising its head above that of its opponent
(Fig. 1b and 1c). Throughout each combat
ritual, the snakes also used their tails to restrain
their opponent by preventing forward
locomotion. Bites were not observed during
rituals.
Observations of male combat
Case #1: One S. pullatus was observed near the
curb of a sidewalk while a second individual
approached. The two paired their heads and a
third individual approached while the other two
were exhibiting courting behaviour. One of the
snakes (probably a male) interrupted the
courtship behaviour to pursue the third
individual, who fled. The “pursuer” returned to
courtship and the third snake, which had been
chased away, approached the courting pair
again. It was pursued a second time and finally
chased away by the “pursuer”. The pair
remained copulated and later were observed
mating on a lemon tree.
Case #2: Three individuals were observed
together, two keeping their heads raised on
display and later in combat. After a short period
two of the snakes engaged in copulation. The
third individual was no longer near the site.
Case #3: This episode occurred on the banks
of a river. Males were entwined and repeatedly
tried to keep the cranial part of their body raised
above their opponent’s. During certain moments,
the tail was used in an attempt to immobilize
the opponent and, on some occasions, it was
possible to observe a brief exposure of the
hemipenis of one individual. Combat occurred
in low-lying vegetation and partly among
26 Herpetological Bulletin 126 (2013)
D.F. Muniz-Da-Silva and S.M. Almeida-Santos
Case Season Date N specimens Combat Copulation
behaviour
Duration Place
#1 Austral spring
12 Oct 2000
3 X X - Cardoso
Island-SP
#2 Austral spring
Oct 2001
3 X X - Cardoso
Island-SP
#3 Austral spring
13 Dec 2007
2 X* - + 1 hr Costa Rica-MS
#4 Austral summer
26 Dec 2012
2 X - + 1 hr Pirenópolis-GO
Table 1. Male-male ritual combat in S. pullatus observed in situ. (x) observed; (-) not observed; (*) hemipe-
nial exposition.
Figure 1. Male-male ritual combat in S. pullatus. A.
The males try to keep their heads as high as possible.
B. The male that is at a disadvantage (white) retreats
its head and loosens a portion of the body twining.
C. After gaining free space with the body, the male
that retreated (white) places its head up again. D. At
this time, this male (white) is able to keep its head
higher than the opponent (black). The arrows indi-
cate the direction of the movement performed by the
individuals.

terrestrial substrate. During combat the snakes
fell off branches. The beginning of the ritual
was not observed and it lasted for approximately
one hour.
Case #4: On a dirt road two males were
sighted already commencing combat. The
snakes kept their bodies entwined throughout
combat, although it was noticeable that the
smaller male intertwined its body more than the
larger male in an attempt to immobilize its
opponent (Fig. 2). After a period approximately
one hour the larger male gave up and retreated
to a tree nearby. The smaller male then chased
the losing individual away.
DISCUSSION
Reproductive behaviour in snakes involves
courtship, copulation, and in some species,
mate guarding or surveillance that can lead to
combat between males (Carpenter, 1977;
Almeida-Santos et al., 1999). Of the
approximately 2700 known species of snakes,
combat has been recorded for only 6% of
species (Schuett et al., 2001).
Combat ritual among colubrids was
described by Carpenter (1977) and reported to
be horizontal, with the snakes rarely raising the
head and neck regions off the ground. The only
previous exceptions were species such as
Elaphe longissima and Ptyas mucosa that raise
the cranial part of the body to try to force the
opponent’s head toward the ground. Almeida-
Santos & Marques (2002) reported that
Chironius did not fit this general pattern for
colubrids since the species displayed a combat
ritual where males tended to maintain the
cranial portion of the body vertical. This posture
of lifting the cranial portion of the body is more
typical of Viperines. S. pullatus also fits the
pattern demonstrated by Chironius and both
genera are semi-arboreal. This suggests that
semi-arboreal colubrids may engage in combat
ritual in a similar manner to viperines and not
adopt a standard horizontal position as other
colubrids do. Although there is a similarity in
the position of the combat ritual of Spilotes with
that of vipers, it appears different because male
vipers often try to push the opponent’s head
against the ground (Carpenter, 1977). This
suggestes that a possible goal of the behaviour
is to restrain, through physical force, the head
of the rival. For S. pullatus the goal of the
combat ritual seems to be to keep the head
higher than that of the opponent, possibly to
boast that it is the larger individual. Schuett
(1997) demonstrated that male size is important
for success in combat and influences mate
selection by females. The fourth ritual (case #4)
showed clearly that larger males are not always
more dominant than smaller ones and it is
possible that a male with more energy may have
the advantage during combat. Combatant snakes
that did not become fatigued in our observations
were able to remain upright and win over
weaker rivals.
Combat in S. pullatus lasted approximately
one hour. Despite the long period of the ritual,
bites or any application of physical damage to
an opponent was not observed, and therefore
the ritual may only result in an energy
expenditure cost for the participating snakes. In
one case (case #1), the males were not observed
commencing a duel but the encounter did not
result in combat. Instead, the dominant male
chased the subordinate male away suggesting
that the cost of energy expenditure, or perhaps
even previous combat experience, may serve as
a deciding factor for males during combat
rituals. In two of the reported cases (case #1 and
#2), three animals were present, two of which
participated in the ritual and the third (female)
observed to copulate with the likely winner of
Male-male ritual combat in Spilotes pullatus
27Herpetological Bulletin 126 (2013)
Figure 2. Two males in combat. Note that the small-
er male (white arrow) tries to immobilize the larger
male (black arrow) keeping his body intertwined
with its opponent.

28 Herpetological Bulletin 126 (2013)
D.F. Muniz-Da-Silva and S.M. Almeida-Santos
the combat. It is possible that proximity of this
nearby female may have incited combat ritual.
Combat behaviour in snakes typically occurs
during the mating season and is mostly related
to copulation (Capula & Luiselli, 1997; Schuett
et al., 2001; Almeida-Santos & Marques, 2002).
In both interactions of Spilotes in the
southeast region on Cardoso Island, Sao Paulo,
combat occurred during early spring, which is
when the final period of copulation for Spilotes
species in the southern hemisphere occurs
(Muniz-Da-Silva, 2012). However, combats
between male Spilotes, observed in the central-
west region, occurred in late spring and early
summer, which does not correspond to the
mating season of the species. During these
events, there were no females present. This may
suggests that male-male combat rituals for S.
pullatus may serve other purposes besides
access to females such as dominance or territory
dispute. Dominance and territory has also been
suggested as a cause of combat for Chironius
bicarinatus (Marques et al., 2009)
In one instance (case #3) exposure of the
hemipenis of one of the snakes was observed
during combat. Almeida-Santos et al. (1998)
also observed this behaviour in Micrurus
frontalis. Behavioural analysis of this
phenomenon is not easily explained and would
require further observations to decipher exact
reason for its function.
ACKNOWLEDGEMENTS.
We thank R. Cogni, P. R. Guimarães Júnior, J.
M. Longo, E. Ayer, R. M. Rodrigues, L. Pizzatto
and C. R. Martins for their important photos,
videos and information that were essential for
elaboration of the manuscript. We also thank V.
F. Czank for illustration in this paper and
Fundação de Amparo à Pesquisa do Estado de
São Paulo (2010/14733-1) and Coordenação de
Aperfeiçoamento de Pessoal de Nível Superior
for financial support. Suggestions for
improvements to the original manuscript by Dr
Todd Lewis greatly improved the final version.
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