systematics of snakes of the dipsas oreas complex - BioOne

118 Bulletin Museum of Comparative Zoology, Vol. 158, No. 3
Species of Dipsas are well known to
prey upon terrestrial gastropods (e.g.,
Cunha and Nascimento, 1993; Martins
and Oliveira, 1998; Peters, 1960a; Sazima,
1989). A single food record is available for
D. oreas from the Río Zaña Study Site.
The posterior portion of the intestine of
ANSP 31777 was packed with slug and/or
snail remains. Terrestrial and arboreal gastropods
were both abundant and diverse
at this locality during the rainy season.
Dipsas oreas exhibits defensive posturing
common among species of Dipsadini
(Cadle and Myers, 2003), including head
triangulation, raising the anterior part of
the body, and bringing the head and neck
back into an S-shaped loop (Fig. 15). Individuals
occasionally added an additional
bend to the loop and the body was often
‘‘anchored’’ with a loose coil. Although
some individuals would occasionally crawl
while holding this posture, none could be
induced to strike.
The posturing and head triangulation defenses
of Dipsas oreas resemble the defensive
behaviors of some vipers (Greene,
1988) and thus are potentially a form of
behavioral mimicry, and perhaps the banding
pattern of D. oreas could resemble that
of some vipers to certain predators. However,
vipers are said by local residents not
to occur at the Río Zaña Study Site, and
none were recovered in my herpetofaunal
sampling there (residents report ‘‘víboras’’
at lower elevations toward the coast; at least
one species, Bothrops roedingeri, potentially
occurs there, although this species is
documented only farther south in the Peruvian
coastal region; cf. Campbell and Lamar,
2004). In other parts of the range of
D. oreas, a possibility exists that one or
more viperid species is sympatric with D.
oreas, judging from distribution maps in
Campbell and Lamar (2004); however, such
sympatry remains to be demonstrated. The
only venomous species potentially occurring
sympatrically with D. oreas at the Río
Zaña Study Site is Micrurus mertensi,
which is a coastal/foothill species (Campbell
and Lamar, 2004) that is recorded in
my collections from 1,300 to 1,400 m at the
site, just short of the lowest recorded elevation
for D. oreas (1,450 m). However,
there is (to my perception) no particular
resemblance between these two species.
Comparisons of Behavior with Other
Species of Dipsas. Species of Dipsas occur
in tropical dry forests and rain forests from
central Mexico to the subtropical zone of
southern Brazil, thus inhabiting an array of
relatively aseasonal to highly seasonal environments.
As indicated for the Río Zaña
Study Site, seasonal activity correlated
with the onset of rains or high ambient
humidity has been reported in other species
of Dipsas inhabiting seasonal environments.
For example, Hartmann et al.
(2002) found that adult D. albifrons were
active only during the rainy season in the
Atlantic forest of southeastern Brazil (juveniles
seemed less seasonal in their activity).
On the other hand, a related snake
from the same region, Sibynomorphus
neuwiedi, is more active during the cooler,
drier season (Marques et al., 2001). Activity
patterns of species of Dipsas from less
seasonal rain forests in equatorial Amazonia
do not show strong seasonality (e.g.,
Martins and Oliveira, 1998).
Cadle and Chuna (1995: footnote 5)
commented on the seemingly paradoxical
behavior of an arboreal snake such as Dipsas
oreas retreating to the ground surface
or subsurface during its inactive period,
rather than seeking arboreal retreats.
However, this behavior could be frequent
in both montane and lowland members of
the genus, as the following remarks indicate
for several species.
Dipsas catesbyi: At La Selva Lodge (Río
Napo, Ecuador) I found an adult Dipsas
catesbyi (not collected) under dead leaves
in deeply shaded forest at 1500 hr. At the
same locality another individual encountered
while active in low vegetation at
night dropped to the ground after several
minutes of observation and hid underneath
the leaf litter. Comments associated
with other specimens include ‘‘on ground