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clutches of 6-44 eggs, but clutches exceeding 24 eggs are rare (Fitch
1963. Copeia 1963:649-658; Wright and Wright 1957. Handbook
of Snakes of the United States and Canada. Cornell Univ. Press,
Ithaca, NewYork. 561 pp.). Although information concerning clutch
size and husbandry is available for captive
E. o. spiloides
(Merker
and Merker 1995. Reptiles 3:56-75; Staszko and Walls 1994. Rat
Snakes. TFH Publications, Neptune City, New Jersey. 208 pp), little
is known about the reproductive biology of wild individuals of this
subspecies. I report the clutch size of
E. o. spiloides in
Shelby
County, Tennessee, USA, at the northwestern extreme of their range
(Conant and Collins 1991. A Field Guide to Reptiles and Amphibians
of Eastern and Central North America. 3rd ed. Houghton Mifflin
Co., Boston, Massachusetts. 450 pp.). During 1994-1997, two
clutches were obtained from females that were gravid when collected
in the field, and one clutch was discovered in a rotting tree stump.
Mass (± 0.5 g) and SVL (± 0.5 cm) were recorded for each female
at the time of collection. One female (772.7 g, 124.5 cm) laid 19
eggs and weighed 523.2 g following oviposition. The other female
(716.5 g, 122.0 cm) laid eight eggs and weighed 583.4 g following
oviposition. Eggs were weighed within 5 h of oviposition; individual
egg mass ranged from 10.12-21.74 g (mean ± SE = 13.51 ± 0.68).
Relative clutch mass (Shine 1980. Oecologia 46:92-100) averaged
33.42 ± 8.37%.
The clutch found in the tree stump contained eight eggs positioned
ca. 75 cm above ground level in a tree stump measuring 25 cm in
basal diameter. Activity by a colony of carpenter ants
(Camponotus
sp.) higher in the stump had encased the snake eggs in a layer of
decaying wood grains.
Following either collection or oviposition, eggs were incubated
at 26-28°C in plastic boxes containing a 1:2 water:vermiculite (by
mass) substrate. Eggs hatched between 30 August and 24 September
following an incubation period of 60-62 days. Eleven of the 41
eggs (26.8%) failed to hatch or produced still-born embryos
following pipping. The sex ratio of the surviving neonates was 1:1.22
female:male.
I thank Tom Norman, Jr. and Dave Frederick for assistance in the
field, and Bill Gutzke for comments on the manuscript.
Submitted by
STEPHEN J. MULLIN,
Department of Biology,
University of Memphis, Memphis, Tennessee 38152-6080, USA.
Present address: Department of Biology, University of Central
Arkansas, Conway, Arkansas 72035, USA; (e-mail:
smullin@mail.uca.edu).
EUNECTES MURINUS
(Green Anaconda).
CAIMAN
PREDATION.
The green anaconda
(Eunectes murinus)
and the
spectacled caiman
(Caiman crocodilus) are
two large predators that
use very similar habitats in the seasonally flooded savannas of South
America. Predation of caimans by anacondas has been reported
(Wehekind 1955. Brit. J. Herpetol. 2:9-13) and appears to occur
often in the llanos (Rivas, unpubl. data). Predation by
Caiman
sclerops
on
Eunectes notaeus
has been reported (Medem 1983. Los
Crocodylia de Suramerica II. Editorial Carrera, Bogota, Colombia.
270 pp.); however, there are no reports of predation by caiman on
the larger
E. murinus.
During a seven-year study of the behavioral
ecology of the anaconda in the Venezuelan Llanos, we observed
spectacled caimans preying on
E. murinus
on three occasions.
On 25 May 1996 we discovered a large caiman (SVL >90 cm)
firmly gripping the head of a radio-implanted female anaconda (494
cm total length, 29 kg), who in turn had wrapped herself around the
caiman's head and neck. After ca. 15 min. the snake relaxed her
coils, apparently losing the struggle with the caiman. When the snake
stopped struggling, we interrupted the event to recover the
transmitter. Because this snake had been found severely wounded
two months before this observation, it is likely that she was not in
top physical shape, and this may have played some role in the attack.
Another observation took place on 29 April 1996 in a roadside
channel covered partially by water hyacinth
(Eichhornia).
A caiman
(SVL >90 cm) was on the left side of the anaconda, gripping it by
the anterior 1/5 of its body. The snake had thrown a loop over the
dorsal surface of the caiman and wrapped its posterior body and
tail around the caiman's left hind leg. The snake, although much
smaller than the caiman, was wrapped so tightly around the hind
leg that the head of the caiman was pulled towards its hindquarters.
The snake periodically tightened its loop, causing the caiman to
flip over to the right and under the water. The caiman repeatedly
attempted to drag the snake out of the water, but each time the
anaconda managed to flip the caiman and pull it back under water.
The wrestling match continued for five hours, often punctuated by
both animals submerging for periods of 10-15 min. Finally, as the
light faded (1900 h), we saw an unidentified caiman of similar size
leaving the area with no snake in its mouth. Five days later we
found a dead male anaconda (247 cm total length, 5.5 kg), with
wounds from a caiman bite on the anterior 1/5 of its body. The
wounds suggest a caiman with estimated measurements of 121 cm
SVL, 43 kg mass, and 29.5 cm skull length (Thorbjarnarson, unpubl.
data). The snake showed no signs of decomposition, indicating a
recent death. We surmise that the snake escaped from the caiman
but subsequently died from its wounds. Judging by the relationship
of masses, we believe that it was the caiman trying to eat the snake
and not vice-versa.
The last observation (19 March 1997) also involved a large caiman
(SVL >90 cm) attacking a small female anaconda (152 cm total
length, 1.7 kg). The caiman was in a small roadside pool with the
snake in its mouth. Upon our approach, the caiman dropped the
seriously wounded female anaconda. Although the snake survived,
we consider this a predation event because the snake was not
struggling when we arrived and thus would not have survived
without our intervention.
In total, we have found twelve dead anacondas (six males and six
females) during the study. Based on our observations and
examination of the anacondas (presence of deep circular bite marks
matching the size and position of caiman teeth), we determined
that all six males and two of the females were killed by spectacled
caimans. Interactions between these two sympatric reptiles seem to
be quite common.
We are in debt to M. Quero and P Azuaje for their cooperation
with the project. W. Holmstrom helped in the data collection and P.
Calle was great help in the implantation of the transmitters. We
also thank P. Andreadis and G. M. Burghardt for editorial comments
on early versions of the manuscript. This research was possible
thanks to grants from The Wildlife Conservation Society, The
National Geographic Society, CITES, and the Venezuela Fish and
Wildlife Service (Profauna). We thank COVEGAN for allowing us
to work on their ranch and for all their cooperation with this project.
Submitted by
JESUS A. RIVAS,
Department of Ecology and
Evolutionary Biology, University of Tennessee, Knoxville Tennessee
37996-0900, USA (e-mail: jrivas@utk.edu),
JOHN B.
THORBJARNARSON,
Wildlife Conservation Society, 2300
Southern Boulevard, Bronx, New York 10460-1099, USA,
MARIA
C. MO10Z,
Graduate Program in Ecology, Departamento de
Biologia de Organismos, Universidad Simon Bolivar, Caracas,
Venezuela, and
RENEE Y. OWENS,
World Society for the
Protection of Animals, 29 Perkins Street, P.O. Box 190, Boston
Massachusetts 02130, USA.
Herpetological Review 30(2), 1999
101
