An unidentified frog was observed by Jack Corbo while on a 2000 expedition to the recently explored portion of the Bladen Nature Reserve, Belize, Central America.

1. 1
Case of an Unidentified Frog Observed in the Bladen Branch
Nature Reserve, Toledo District, Belize, Central America
Jack M. Corbo
************
South Euclid, OH 44121
Abstract
The Maya Mountains in the Bladen Nature
Reserve of Belize have only recently been
explored in the last 30 years. On a 2000
expedition to the region, the author sited in
Muklebal Tzul valley a species of anuarian that
could not be identified. The anecdotal
description of the frog in this publication was
observed on the gravel bank of Cave creek: a
tributary of the upper Bladen River that is the
eastern branch of the Monkey River drainage.
Introduction
In 1525, Hernán Cortés cursed the arduous
terrain of the Maya Mountains of southern
Belize as he led an expedition around the range
to subdue the local Mayas, then a backwater of
their realm. Though not very high, the
inaccessibility of this mountain range prevented
their crossing until 1875 while the highest
summit, Doyle’s Delight, was first accented as
recently as 1987 (Kindon, 2002). Exploration is
difficult due to the steeply eroded knife-like
karst limestone composition that is further
isolated by dense stands of impenetrable
seasonal rain forest. This “terra incognita” (it
was also referred to as “Lost World” by the
expedition director) aspect was the very reason
that a local university archeologist directed a
series of archeological expeditions to the Maya
Mountains for a decade starting in the 1990’s
(Dunham, 1995: Dunham, 2009). With the
discovery of several previously undocumented
Mayan out-post cities on earlier expeditions, the
very unexplored nature of the Maya Mountains
led me to conclude that significant biological
findings could also be made.
Due to the cross-disciplinary nature of the
expeditions and as a then biology PhD student, I
was invited to be a member of the 1999 and
2000 expeditions deep into the 99,687 acre
Bladen Branch Nature Reserve. A region of the
upper Monkey River drainage and then the main
area of my field research.
Although the objective of this paper is to
describe an unidentified frog seen on one of
these expeditions, it also provides an
opportunity to document the serendipitous
nature and pitfalls of scientific field
investigations (the first half of this paper). Such
obstacles can possibly lead to discoveries
outside the intended area of research.
Background
Guides at the front of our procession used
machetes to advance a trail through the tick
infested forest undergrowth to our field camp.
Some of the Mayans we employed had
improvised backpacks made of used white rice
sacks of nylon that were supported by a thinned
palm leaf used as a trump line across their
foreheads. I recognized this as a traditional
method of portage chronicled as far back as the
Spanish conquest (Ross, 1978).
Occasionally abandoned logging trails (the
region was known for its lucrative mahogany
trade in the late 19th and early 20th centuries) or
sun-baked dry riverbeds (during the rainy
season from July to December they become
lethal torrents) were incorporated into the trail.
The dry riverbed of lower Bladen River, a
collapsed river cave, had the added drudgery of
enormous weathered limestone boulders some
the size of small houses littering the trail.
Dubbed “Rock Shoot”, despite the hardship of
climbing over or squeezing between these
obstacles to reach our destination, I learned to
welcome this last leg of our trek. It was located
near field camp and heralded an end of a

2. 2
grueling 16 km, day-and-a-half inland hike that
began at a logging road off Belize’s Southern
Highway.
Two field camps were established to
accommodate our roughly thirty-member
expedition crew. The first was located at the
eastern end of AC valley where the middle
Bladen River exited AC cave. The valley and
cave were so-named for a much welcomed air-
conditioned-like microclimate that emanated
from the cave and permeated our canopy-shaded
camp. A smaller camp was set up in the larger
neighboring Muklebal Tzul (“Mooklaybahl
Tzool”) valley.
The fieldwork was tedious; often pestered by
malarial mosquitoes, which I caught in 1999,
and botflies whose parasitic larvae I was
routinely infested with in numbers too high to
count (the juvenile insects burrow below and
feed on skin tissue). Out of desperation I
developed a reliable method to remove these
pests on the 2000 expedition by placing a drop
of insecticide on their breathing hole. After a
few minutes, the infested area of skin was
thoroughly washed (many of the insecticides in
Belize contain DDT). After a days wait, the
decomposing pest loosened its grip and could be
extracted by applying pressure like popping a zit
(the botfly larvae have three rows of spikes
surrounding their thorax that otherwise prevent
easy extraction even when freshly killed).
Other dangers in the field were the venomous
fur-de-Lance (Bothrops asper) and herds of
White-Lipped Peccaries (Tayasuu pecan), the
latter mauled one unfortunate expedition
member on our 2000 expedition. We had to
vicariously call-in via satellite phone to
Washington DC a Royal British Army
helicopter from the capital of Belize City some
112 km (70 miles) away. The dusk casualty
evacuation was made at a helicopter landing
area we routinely had cut from the forest near
our field camp as a precaution. I vividly
remember one expedition member treating the 2
inch long by 1 inch deep rear wound caused by
the tusk of these animals with iodine from my
tissue sampling kit for turtles as we waited for
the helicopter on the edge of the field.
Initially I planed to study the population
genetics of Kinosternon leucostomum (White-
lipped Mud Turtle) for my field research. On
later expeditions, a fish species, Heterondria
bimaculata (False Swordtail) and Pachychilus
indiorum (Jute Snail) were added. These were
all commonly found species in the middle
Bladen River and chosen for their varying
degrees of mobility and ease of identification.
They were also easily captured during the dry
season (January to June) when portions of the
river’s course and its tributaries run dry forming
stagnant pools that force aquatic life to
congregate in abnormally large numbers. This
was especially helpful the in the capture of K.
leucostomum which were found in high
densities hiding in the decomposing leaf litter at
the bottom of the streambeds. I intended to
extract DNA from tissue samples collected from
the three species and sequence small genomic
domains to determine if tributary animal
populations have unique genetic characteristics
specific to each stream in the study area.
Figure 1. Map of Bladen River drainage found
in the southwestern region of the Bladen Branch
Nature Reserve, Toledo District in southern
Belize. AC and Muklebal Tzul field camps are
represented by the large and small solid circles,
respectively. The helicopter landing area is
represented by the square. AC Cave is depicted
by the doted line between the two field camps.
The unidentified frog was sited in May of 2000
on the bank of Cave Creek within an estimated
300 m upstream from the Muklebal Tzul valley
field camp.

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The streams in the investigation were Ek Xux
(“Eck Shoosh”) creek and the middle Bladen
River: tributaries to the lower Bladen River
(Figure 1). Ek Xux creek courses over volcanic
bedrock making its water slightly acidic and
inhospitable to P. indiorum unlike the limestone
bedrock of middle Bladen River that has
carbonate rich water, a favorable habitat for the
snail (Corbo, 2000). The availability of the P.
indiorum in one tributary and its absence from
another provide potentially different diets for K.
leucostomum, which inhabits both tributaries. I
hypothesized and attempted to prove that
populations of K. leucostomum, develop minor
genetic variations to cope with these different
food resources. My main interest was the
genetic analysis of animal populations in the
tributaries as well as the genetic analysis of the
animal populations at the tributaries’
convergence. Just as the waters of the two
converging tributaries mix, the animal
subpopulations of the same species inhabiting
different tributaries also merge and interbreed
with upstream subpopulations. I further
hypothesized that a genetic mixing downstream
of subpopulations could preserve adaptive traits
uniquely advantageous to upstream tributary
environments. This archiving mechanism would
be useful for recolonization if an upstream
tributary subpopulation was catastrophically
extirpated. In other words, when upstream
genetic traits are introduced to downstream
populations the traits have the potential to be
reintroduced by recolonization and
establishment of a recovering upstream
subpopulation in the advent of a prior upstream
population catastrophe. Otherwise advantageous
adaptive traits would be permanently lost if they
were solely restricted to drought vulnerable
upstream populations and would have to form
again a priori.
A GPS survey made by the author (with
assistance from guides Norman Chaco and Ben
Rash) on the hydrology of Ex Xux creek and
middle Bladen River indicated approximately
half their lower course ran dry during the dry
season. Streamsinks (where the river runs
underground) potentially isolate upstream
populations from those downstream where a
resurgence was observed at the convergence of
these two streambeds. Lethal catastrophes could
conceivably occur during an abnormally hot dry
season where an upstream tributary would
completely run dry only to become habitable
again with a continuous flow of the tributary
during the rainy season. Such research would
provide a mechanism for riparian species to
maintain or rapidly regain portion of its range
(by the inbreeding expression of beneficial
recessive traits) lost during environmental
catastrophic events.
Preliminary d-loop CR mtDNA sequence
phylogenetic analysis was made on eleven K.
leucostomum collected from three sites (with
one out group specimen from Nicaragua)
suggested there were no clear subpopulations.
The turtles caught at the Muklebal Tzul pool
near the entrance to AC Cave, AC valley, and
Ek Xux creek showed evidence of migration
between the sites (van Keulen, 2003), even
though they were separated by steep karst
mountain terrain or connected by tortuous
caves.
Regrettably time restrictions, funding
problems and a near direct hit to the study area
by hurricane Iris in 2001 (making trails to the
field camp cut in previous years impassible with
fallen timber) prevented me from obtaining the
PhD. But it was on the 2000 expedition during a
field excursion to capture K. leucostomum in
late May that I sited a cream colored frog that is
the subject of this paper.
Study Area
The approximately 8.75 km2 (roughly 4 km
long) Muklebal Tzul valley derives its name
from Q’eqchi’ Maya meaning “Hill of Many
Tombs” (Kindon, 2002). The ruined structures
(211 were counted) in this valley were built of
eroded rectilinear limestone slabs, collected
from local rock outcrops and piled up to 7 m
high to build monumental ceremonial structures
with civic plazas, tombs, and house mounds (a
remote area of the canyon was also found to
have stone-faced agricultural terraces). Far from
the better-known Mayan archeological sites like

4. 4
Tikal or Palenque, no elaborate carvings or
hieroglyphics were found after the site was
bushed (cleared of vegetation by machetes
wielding guides). Ornamentation was likely
painted rather than carved on any architectural
stonework and had long since weathered away.
The Muklebal Tzul archeological site is
thought to be a backwater settlement established
during the Maya Late Classic as a frontier
kingdom dating roughly AD 700-850. This
remote mountainous city had a population
estimate (based on the number of house mounds
surveyed multiplied by the average number of
ethnic Mayans occupying a contemporary
house) at the height of occupation of 1,146
people (Kindon, 2002). A more updated
interpretation of the site is that the city was
founded to exploit mineral resources much like
the modern mining city of Denver, Colorado.
The region is thought to be an economic source
for quarried raw materials like granite for
grinding stones. Mineral pigments such as red
hematite was another material traded to lowland
Mayan cities far downstream toward the
Caribbean coast. The area is also rich in cave
formations that had religious significance to the
Maya. I particularly remember Mayehal Xheton
Cave which had the remnants of a 10 m wide
elevated plaster platform (stage) constructed in
front. The entrance was narrow with a natural
pointed arch flanked by a second smaller cave
giving the cliff face a cathedral-like facade.
Other caves had a more practical use where the
cooler temperatures were exploited to store
presumably corn. Large empty ollas, round-
bottom short-necked ceramic storage vessels up
to 60 cm (2 ft) in diameter, were found intact in
some of theses dry caves (Prufer, 2002).
The 2000 MMAP expedition had an
archeological survey conducted on the Mayan
ruins and limestone caves of Muklebal Tzul
valley. The smaller field camp was set up to
accommodate three archeological graduate
students and a support team of Belizean field
technicians. I was invited from AC field camp
along with two guides, Ben Rash then from the
town of Big Falls and Sebastian “Besh” Rash
then from the village of Silver Creek, to expand
my fieldwork into this adjacent canyon (two
guides always assisted me, in the case of an
emergency one of our party stayed with the
injured while the other ran to a field camp for
help).
The Muklebal Tzul valley field camp was
located on Cave Creek which served as the
camp’s water source. Another aquatic habitat
found in the eastern side of this canyon was
small 3 m wide pool that had a high density of
K. leucostomum: five adult female, eight adult
male, and five hatchlings (Corbo, 2000).
Situated in the riverbed of the dry upper Bladen
River, I suspected this stagnant pool acted as an
oasis/nursery that sustained the turtles until the
rainy season resumed the continuous flow of the
river. This would explain the accumulation in
the pool of 1.5 ppm dissolved ammonia
(TetraTest® Ammonia; Corbo, 2000) making it
potentially deadly for fish and presumably
amphibians. An artificial source of water devoid
of aquatic life was found at the Muklebal Tzul
archeological site where an intact 13 m long by
1 m high horizontal well was constructed
sidewise 2 m below the civic stelae plaza
(Prufer, 2002) at the core of the ruined city. The
once plaster lined tunnel ended in natural spring
flowing from a fist-sized fissure. The proximity
and low volume likely made it an exclusive
water source, insufficient to supply for the entire
city’s population during the dry season.
Habitat
Cave Creek flows through an Evergreen
Broadleaf Forrest in the Maya Mountains at an
elevation of 370 m (Meyers, Farneti, and Foster,
1996). A primary stream, the width was variable
with a maximum of 2 m and no more than 50
cm deep with a current estimated to be less than
4 m/min. Downstream of our field camp, a
stream sink caused the creek channel to run dry
as it followed the northeastern wall of the valley
where it converged with the dry streambed of
upper Bladen River. The river channel then
entered AC Cave which tunnels through the
eastern side of Muklebal Tzul valley. Tree
trunks snagged in the 15 m high ceiling at the
opening of the cave (observed by previous

5. 5
researchers) attested to the depth of severe
flooding that can occur during the rainy season.
I planned to make biological collections
upstream of Cave Creek to its source, but our
efforts ended after we encountered a 10 m
vertical waterfall in a narrowed branch of the
canyon. Located 1 km from the field camp, the
falls were climbed by both accompanying field
technicians who found yet another waterfall of
equal height above, suggesting that we were at
or near the rim of the valley. None of organisms
in my primary study (K. leucostomum, H.
bimaculata, and P. indiorum) were observed in
our survey.
The absence of the P. indiorum is especially
noteworthy in that it suggests an acidic water
chemistry as was also observed in neighboring
Ek Xux creek in the adjacent valley which had a
GH/KH of 0 ppm (GH/KH TetraTest®:
measurement of dissolved carbonates needed for
shell formation; Corbo, 2000) and a acidic pH
of 6.5 (pH TetraTest®; Corbo, 2000). Rain
runoff over a predominance of volcanic bedrock
in these two valleys is the likely cause for the
acidic water chemistry (Bateson and Hall,
1977). A resurgent cave spring roughly 60 m
from downstream entrance of AC Cave formed
the headwaters of the middle Bladen River
which registered a higher alkaline pH range of
7.5-8.6 and KH/GH range of 35-122 ppm
(Corbo, 2000). The higher alkaline water
chemistry of the down stream middle Bladen
River is likely the byproduct of dissolved
carbonates released by the acidic headwaters
from limestone strata that makeup AC Cave and
the riverbed. As a consequence of the high
KH/GH, unlike its upstream counterpart, the
middle Bladen River as it exited AC Cave had
an abundance of P. indiorum populations.
Description of Unidentified Frog
About 300 m upstream from the field camp
we observed the frog in question on the northern
side of Cave Creek which in this area was less
than a 1 m wide and not more than 10 cm deep.
The frog was seen for less than a minute by the
technicians and author in the midmorning
suggesting a diurnal behavior. It sat in a
stationary posture roughly 10 cm from the
stream northern edge on a damp, shaded
graveled bank. As depicted in Figure 2, the frog
had the appearance of a terrestrial species with
two prominent characteristics. The first and
most notable was a lack of dermal pigmentation
with a uniformly smooth cream-colored skin
with no notable blotches, striping or tubercles
(ventral skin pigmentation was not observed and
there may have been a darkened face mask
around the eyes). The second distinguishing
characteristic was the dorsalateral black eyes
with no discernable iris and the same diameter
as the medium sized tympanum. The interorbital
distance was roughly 15 mm. There were no
terminal discs observed on the fingers as are
found on tree frogs, which confirmed its
terrestrial behavior. A dorsalateral fold was
observed, the snout was rounded and the snout-
vent length was about 7.5 cm with a general
body shape was reminiscence of the genus
Rana.
Figure 2. Drawing made in 2004 by the author
of an unidentified frog observed at Cave Creek,
a tributary to the upper Bladen River (a branch
of the Monkey River), on a 2000 expedition to
Muklebal Tzul valley, Belize. Distinguishing
characteristics were the cream-colored skin and
black eyes. The frog appeared to be a terrestrial
species with a body shape of genus Rana.
One of my accompanying field technicians
dissuaded my attempts to hand capture the frog
as I straddled the stream in pursuit of the

6. 6
ambivalent anuran. He implied that it was a
common species and was not worthy of an
investigation. In hindsight as we resumed our
upstream survey, I regretted heeding this advice
and on our return downstream to the field camp
two hours later found that the frog was absent
from the site. A similar frog was seen by the
author a year earlier in the 1999 expedition in
the same region. The amphibian was observed
in the center of the mostly dry riverbed of the
middle Bladen River sitting on the damp clay
edge of very small 1 m crescent shaped pool. A
large boulder on the downstream side shaded
the muddy pool and its occupants from the
glaring tropical sun. This frog was darker and
likely not the same species seen at Cave Creek.
On a later expedition in 2003 to the valley of
Dam Creek (more than 16 km from east of Cave
Creek) in the eastern foothills of the Maya
Mountains near the town of Medina Bank the
frog was not observed. A flyer with the
illustration of the frog in Figure 2 was kindly
handed out to local workers by the co-director
of the 2004 Uxbenka: another university
archeological expedition site located at the
southern foothills of the Maya Mountains. No
response was received of the frog inhabiting this
region either, suggesting a restricted, not
cosmopolitan, range (Wanyerka, 2005). The
species is apparently confined to the interior of
the Maya Mountains, endemic perhaps solely to
Muklebal Tzul valley. The appearance of the
frog was reminiscent to the author specifically
to Rana Sylvatica (North American Wood Frog)
in size and morphology with a lack of skin
pigmentation.
Native Frog Candidates
A review of known frogs inhabiting Belize
provided four candidates for the frog seen at
Cave Creek (Meyer, Farneti, and Foster, 1996).
Rana juliani (Maya Mountains Frog) ranges in
the area, but its color is medium brown with
dark brown markings unlike the lighter colored
skin of the Cave Creek frog. Eleutherodactylus
laticeps (Broadhead Rainfrog) is a similar size
as the Cave Creek frog, but again as with R.
juliani the dorsal color is a medium to dark
brown, too dark to be a match for the Cave
Creek frog. Eleutherodactylus rhodopis
(Lowland Rainfrog) ranges in northern Belize
and is smaller than the unidentified frog as is
Eleutherodactylus chac (Maya Mountains
Rainfrog) which also has dark bands on its legs.
Another possibility is that a known frog from
neighboring regions intruded its range into the
study area. A review of frogs that range in
nearby countries had none of the characteristics
observed on the frog seen at Cave Creek
(Cambell, 1988).
The geography of Muklebal Tzul valley
provides favorable conditions for the
unidentified frog to be a color variant or
subspecies of the known frogs mentioned above.
The steep karst canyon walls can act as
migration barriers, essentially biological islands
that isolate local frog populations promoting
inbreeding and the expression of recessive genes
such as a leucistic genotype (Bachtel, 1995).
Pale leucistic phenotypes typically though not
aways have eyes that are light color unlike the
black eyes of the Cave Creek frog, making it a
color variant of a local frog unlikely. The
abundance of caves in the canyon and lack of
skin pigmentation lend a second possibility, the
frog is not adapted to epigean (surface)
environments but rather a species adapted to
hypogean (subterranian) environments.
Reduction of skin pigmentation is one
characteristic of troglobites, organisms that have
undergone regressive evolution living their
entire life cycle in caves (environments also
considered biological islands). Because the frog
was observed roughly 0.5 km outside the nearest
known cave, it is more appropriately called a
trogloxene: species that live in but are not
completely dependent on caves (Gillieson,
1996; Wilkins, Culver, and Humphreys, 2000).
AC Cave was explored on a different project, I
was collaborating with the American Cancer
Society, Natural Products Division, in the
collection of cave soil samples to isolate species
of fungus that would provide new variety of
antibiotics, much like penicillin. During the
arduous walk through the cave to collect soil
samples, although not conducted as
herpetological survey, no amphibians were
observed. As mentioned earlier, this region has

7. 7
an abundance of caves which does not exclude
the possibility that the frog originated from
another.
Recommendations
The description of the frog observed at Cave
Creek is admittedly anecdotal. The objective of
this paper is to encourage other researchers
working in the middle Bladen River to further
investigate frog species in this stream Photo
documentation and tissue samples for genetic
analysis are needed to determine its taxonomy
and confirm if it is actually an undocumented
species of frog. A herpetofaunal survey is
recommended during the dry season for
Muklebal Tzul valley with emphasis on Cave
Creek. To my knowledge the region where the
unidentified frog was sited, Cave Creek in the
Bladen Branch Nature Reserve, has not since
been revisited to the extent of the 2000
expedition.
Authors note: correspondence with another
2000 expedition member who was a native of
southern Belize indicated that that he also
observed a strange translucent shrimp inhabiting
one of caves in the study region (Cal, 2013).
Photos of the some of the sites in this paper can
be viewed on my Facebook timeline (1999-
2003).
.
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