the Gigantes
Geckos, cave frogs, and
small land-bridge islands
in the Visayan sea
By Rafe M. Brown and Angel C. Alcala
Photos by Rafe M. Brown
Top: Gigante South Island: denuded, the
forest completely removed in the last 30
years. Bottom left: A close up of the coast
line on the southern shores of Gigante
South Island. The sheared face of the
porous limestone karst rising from the
sea with very little beach appears to be
ideal habitat for Gekko gigante. Note the
cave just left of center and the scrubby
secondary vegetation atop the limestone
formations. Bottom right: Our first
glimpse of Gigante South Island.
n June 1968, Lawton Alcala led a collecting party that explored Gigante South Island as part
of a biological survey to explore the small islands in the Visayan sea, which consists of the
islands of Tablas, Romblon, Masbate, Leyte, Biliran, Cebu, Panay, and Negros. The herpetological survey effort was part of Walter Brown and Angel Alcala’s long-term collaboration
(1955 until present) to catalogue and describe the diverse amphibians and reptiles of the
Philippines. Before this, some sites on the archipelago’s larger islands had been moderately
well studied but no systematic effort had been advanced to address the herpetological communities on smaller islands (i.e. 1,000 to 30,000 square hectares). This effort was important
because only through the arduous collection of the baseline species distribution data that we
are now able to appreciate the staggering levels of Philippine biodiversity and endemicity. To
date, it remains largely due to the efforts of these initial surveys that the puzzling ability of
some small islands to harbor endemic Philippine biological treasures has come to light.
OCTOBER NOVEMBER DECEMBER 2000
HARING IBON
•19•
This is the first live Platymantis insulatus observed by biologists in 32 years. It was photographed outside a small cave where it was spotted at 7 p.m.
just after sunset.
Lawton Alcala however was not preoccupied about these issues at
the time; he was too busy catching frogs, lizards, and snakes for his
herpetologist brother. He may even have been thinking about the giant
python rumored to inhabit the cave he was about to enter. Lawton ducked
into a small coastal limestone cave with the sound of pounding surf
behind him. As his eyes adjusted to the shadows, he detected movement in the dim light. Recognizing the motion as that of a frog on the
cave floor, he rapidly scooped up the retreating animal and held it up to
the light for a better look. In his hand, Lawton Alcala held the first specimen of a strange species that was eventually described as the Island
Forest Frog Platymantis insulatus.
Since the formal description of the species
in 1970, the Island Forest Frog’s strangely
combined morphological and biogeographical
attributes have baffled frog biologists.
Platymantis insulatus is related to other forest
frogs in the Platymantis guentheri species
group; all are moist forest species that call and
nest in trees. However, the Island Forest Frog
lives on the ground among rocks around the
mouths of small karst caves, and nests in limestone crevices. Seems hard to imagine that a
population of rainforest tree frogs could become isolated over thousands of years, diverge
and adopt a terrestrial lifestyle, and invade cave
habitats on a tiny land-bridge island. That a
•20•
small land-bridge island (that was connected
to Panay as recently as 10,000 to 18,000 years
ago but now separated by a shallow channel)
should support an endemic forest species absent (as far as we know) on the nearby relatively large Visayan aggregate island complex
of Panay, Negros, Cebu, and Masbate makes
no biogeographical sense. The only other two
frog species collected as part of the initial survey were the commonly introduced species associated with agricultural areas: the Brackish
water Frog Rana cancrivora and the Common
Tree Frog Polypedates leucomystax. Despite
expectations and overwhelming odds, the presence of Platymantis insulatus is undeniable:
HARING IBON
an endemic species known only in the Gigante
Islands, a Philippine national treasure and a
curious addition to the archipelago’s immense
biological wealth.
The next few years after Lawton Alcala’s
discovery determined that Gigante supports not
only an endemic frog, but a unique gecko species as well. While collecting in the same caves
where Platymantis insulatus was discovered,
Lawton Alcala had also captured a few specimens of a pale pink and gray gecko from cracks
in the cave walls. In 1974, Brown and Alcala
published the description of the Gigante Cave
Gecko Gekko gigante. The probability that
Gigante Island could harbor not only a unique
frog but also an endemic gecko species seemed
unbelievable.
To our knowledge, only one other group of
biologists—Alcala and Luchavez’s team made
a brief visit in the mid-1980s—have been to
the Gigante island group since the initial surveys. In the intervening years, the original forest has been cut down on both the southern
and northern islands. What remains is scrubby
and stunted vegetation. With the forest gone,
conditions on Gigante changed as they have
throughout most of the Philippines’ previously
forested low elevation areas: water became
scarce as the local microclimate turned arid.
The absence of shade trees makes the ground
hot and dry, and the rainy season erodes the
topsoil into the porous limestone beneath.
These are not conditions that bode well for amOCTOBER NOVEMBER DECEMBER 2000
Gekko gigante! Photographed on the wall of its preferred cave habitat where it’s active at mid day.
phibian and reptile populations.
These in mind, we set out to visit the Gigante
islands to determine if Platymantis insulatus
and Gekko gigante still survive 32 years after
their discovery. Our aim was to locate these
species, assess their habitat requirements, conservation status, and chances for continued survival. Truth is, we prepared for the probability that both species were extinct. Several recent attempts to find similarly rare Philippine
species have ended in disappointment, and the
tion, sheer limestone cliffs, and a white strip
of sand beset with coconut trees. A half hour
tour of the Southeast coast of South Gigante
revealed a picturesque tropical island coastline that was nonetheless a poor candidate for
forest frog populations.
Eventually we pulled the boat onto a stretch
of beach near a small cave. We waded in for a
look. The cave entrance showed years of human disturbance: graffiti and fire scars marked
the limestone, broken bottles and trash cov-
an alarmed Gekko gigante. Within minutes, we
had located eight more individuals from between 10 and 50 meters deep within the cave.
Our mixed emotions are hard to describe. It is
impossible to be a biologist working in the
Philippines in this day and age and not be awestruck while standing before Gekko gigante in
a small cave on an island in the Visayan sea,
knowing that we were only the second party
of biologists to gaze on live individuals of this
species, and knowing that they exist nowhere
It is impossible to be a biologist working in the Philippines in this day and age and not be awestruck while standing before Gekko gigante in a small cave on an island in the Visayan Sea,
knowing that we were only the second party of biologists to gaze on live individuals of this
species, and knowing that they exist nowhere else on the planet.
possibility that we would travel to Gigante and
find that both of its endemics had survived
seemed extremely unlikely. Nevertheless, with
the help of the Sagay City mayor who graciously provided a large boat, we embarked
for Gigante from the Northern Negros town
of Sagay in late May 2000.
The six-hour trip took us into the Visayan
sea, past Tagubanhan, Igbon, Pan de Azucar,
and Sicogon islands. We first saw the Gigante
groups in the late afternoon. As we drew close,
we made out denuded hills, scrubby vegetaOCTOBER NOVEMBER DECEMBER 2000
ered the ground. We silently entered, expecting the worst. However, our enthusiasm increased after proceeding about 10 meters when
we saw a large cluster of white eggs in a crack
on the cave wall. The oval shape and manner
in which they had been cemented to the wall
suggested that they belonged to gekkonid lizards. Within moments one of us saw the reflection of his headlamp in the eyes of a small
animal.
We hurried deeper into the darkness and
found, staring down at us from the cave roof,
HARING IBON
else on the planet. Satisfied and happy to see
that at least one of the Gigante endemics was
not extinct, four rolls of film was spent photographing the geckos, their eggs, and the habitat. After a visit to the village head to get permission to make further explorations, we
waded back to the boat so we could find a site
suitable for frog-searching after nightfall.
As we motored around the north coast of
the island, we saw numerous limestone outcrops, all with small caves that we assumed
were excellent habitat for Gekko gigante.
•21•
The small cave where we found Gecko gigante.
Later, we anchored near a small human
settlement on North Gigante, by a patch of
scrubby second growth forest, the sounds of
children playing in the surf within earshot. We
watched a family of eight, who lived in nearby
thatched huts, pry open mussel shells gathered
from a nearby rocky coastline. The shells and
bodies of the animals were discarded after removing the closure muscle that fetched a few
pesos per kilo in the fish markets of small
towns in northeast Panay. Like many other
small islands, virtually all consumable natural
resources had been exploitatively harvested;
the forest is gone, fishing is poor because of
reef damage. The local human population had
been reduced to a few small villages, nonsustainably harvesting the last of available food
sources to make a living.
As the sun set, we put on headlamps and
walked along a small trail into the scrub. Before darkness had completely fallen, we heard
a strange frog call that we couldn’t identify. It
had characteristics of the calls of some Philippine species of microhylids and rhacophorids,
and sounded like a slow rattle, decreasing in
frequency. After half an hour of searching, we
found a small cave opening and there, perched
on the limestone rock, was the Island Forest
Frog Platymantis insulatus.
Our amazement was profound. Excitedly,
we spread out and found more individuals on
the ground and atop large rocks. We extensively photographed the species but were not
able to obtain a quality recording of its mating
call. Soon it was time to return to the boat.
Our disappointment at not being able to obtain a recording of the advertisement call of
Platymantis insulatus was tempered by the
thought that the species appeared to be surviving well, no doubt escaping the heat of the
Visayan sun by crawling into caves and limestone crevices underground. Their survival is
even more remarkable considering that their
large eggs need sufficient moisture to develop
directly into froglets.
That night on the boat, a squall came up. It
•22•
threatened to rip our anchorage
free and set the boat adrift beyond
the protective harbor where we
stayed. As the wind picked up
speed, heavy rain pounded the
craft and soaked us and most of our
gear. We spent the night huddled
in the rain as the wind violently
shaked the boat. The crew replaced
anchors as these were ripped free
by the strong surf. We were unable
to sleep or even rest.
In the morning, we motored towards the beach and attempted to
dry under the morning sun. Standing on the beach among coconut
trees, in the last place we would
expect to hear a rainforest tree frog
call, we heard a chorus of Platymantis insulatus calling from limestone boulders uphill. We quickly gathered our recording equipment and for the next half-hour recorded the strange call of the Island Forest
Frog, this time as it called from under limestone boulders on a scrubby hillside at dawn.
Soon it was time to go. We returned to the boat
blissfully but exhausted too from lack of sleep.
Apparently, both the Gigante island group
endemics are not only surviving, but possibly
thriving in their severely altered habitat. Both
appear to be afforded some protection from
the heat and dryness of the severely impacted
habitat because they live in caves or in deep
crevices in limestone outcrops. Just how far
underground they go and what their preferred
microclimates are, we cannot say.
Exactly how these species evolved the suite
of behaviors that allow them to survive the loss
of the forest can never be determined with any
certainty. But it is tempting to imagine that
after Gigante was once again disconnected
from Panay by rising sea levels at the end of
the Pleistocene, the isolated microclimate became increasingly arid as Gigante’s small forest fragments became disconnected and climatically isolated from the forests of east
Panay. It may have been during this period of
isolation and local microclimate change that
Gigante’s forest frog population adopted the
subterranean, cave-dwelling lifestyle that has
given it the ability to escape the scorching sun
of the Visayan sea. The rainy season between
May and October probably provides moisture
in the microhabitats and the evaporation of
water could maintain relatively low temperatures in these microhabitats throughout the
year.
Again, we will never know for certain. One
thing for sure is that we cannot generalize from
the Gigante situation. This unusual species is
a unique case, perhaps “pre-adapted” to drier
microhabitats, and not at all like the usual Philippine rainforest frogs whose populations crash
with selective logging and are extinguished
when the forest is felled. Platymantis insulatus
HARING IBON
is most probably the product of thousands of
years of evolution in an isolated and climatically extreme, small island microclimate and,
as such, the species has probably persisted by
gradually changing along with its local environment. We cannot conclude from this example that forest species can be expected to
survive the loss of their forest habitat as
Platymantis insulatus and Gekko gigante have
done. In fact, it would be premature to conclude that these species are out of danger of
extinction. We cannot be certain what the next
generation of habitat modification will bring.
And our casual observations, though tremendously exciting for us, should not take the place
of a genuine population survey and rapid protection measures. These should be undertaken
to establish the conservation status and continued survival of both species.
At present, it is not too late for the preservation of these two Gigante endemics, but ensuring their continued existence is an opportunity that must be seized by the conservation
community in the Philippines.
Lessons from our experience may be extended to other small land-bridge islands long
ignored by biologists who believed these had
no potential for endemic species. There are
more than 7,100 islands in the Philippines.
Thousands of these are small like the Gigantes.
And while all await our attention, some still
support undiscovered species that will require
well organized conservation initiatives to survive.
Rafe Brown first began work in the Philippines in 1991. Since then, he has made 11 excursions to the archipelago to study its
herpetofauna. He is currently working on his
Ph.D. at the University of Texas at Austin, USA.
He collaborates with US and Filipino biologists on studies of the systematics, biogeography, and behavioral ecology of Philippine amphibians and reptiles. He first collaborated
with Dr. Alcala in 1997. He has authored 14
papers on Philippine frogs, lizards, and snakes.
Rafe’s dissertation is on the evolution of communication in frogs of the genus Platymantis.
A one-time member of the Haribon Board
of Trustees, Dr. Angel C. Alcala earned his
Ph.D. from Stanford University, Stanford, California. He is a former Secretary of the Department of Environment and Natural Resources,
and subsequently, Chair of the Commission on
Higher Education. Currently, he is the Director of the Silliman University-Angelo King
Center for Research and Environmental Management. Based on his collaborative work during the past 44 years with Dr. Walter C. Brown
of the California Academy of Sciences, he has
published about 70 papers and books on the
systematics, ecology, and natural history of
Philippine amphibians and reptiles.
OCTOBER NOVEMBER DECEMBER 2000