by Rafe M. Brown, Renato Boying Fernandez, Chrisostomo Rivero

Mt. Isarog’s
Herpetological
Wonders
by Rafe M. Brown, Renato Boying Fernandez, Chrisostomo Rivero,
Ricardo Buenviaje, and Arvin Diesmos
photos by Rafe M. Brown
n the past several hundred years, as the forests of the Bicol Region
have been almost completely felled, the tremendous economic and
social importance of the montane forests of Mt. Isarog (Camarines
Sur and Norte Provinces) has become abundantly clear to the surrounding human population. At the same time, this mountain has become
internationally recognized as one of the Philippine’s most fragile and
treasured centers of biological diversity. Surrounding communities depend heavily on the pristine forests of Mt. Isarog for clean drinking
water, building materials, medicinal plants, renewable forest resources
such as rattan and palm, important sources of protein (from low scale
subsistence hunting), and water for irrigation in nearby lowlands.
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Recent biological survey efforts have demonstrated the
highly unique nature of the mountain’s mammal and bird
faunas, and the few available published reports suggest
that the same may be true for Mt. Isarog’s amphibians
and reptiles. At the start of our study, we hoped to
ascertain to what degree the amphibian and reptile
faunas of Mt. Isarog are also locally unique, to identify
species of special concern for conservation efforts, to
learn from local communities about the diversity, uses,
and beliefs surrounding Mt. Isarog’s herpetofauna, and
to contribute to local environmental education, pride,
and increased awareness of the mountain’s amphibian
and reptile communities.
During July and August 2001, with the cooperation
and guidance of the Parks and Wildlife Bureau of the
Department of the Environment and Natural Resources
(PAWB-DENR) and the Naga City Provincial Environment and Natural Resources Office (PENRO), biologists
from the Haribon Foundation, the University of Texas,
and the Mt. Isarog National Park Protected Area Management Board joined collaborators for a preliminary
survey of the herpetological fauna of Mt. Isarog’s
higher montane forests. Here we present a first
glimpse at the unique and spectacular diversity of Mt.
Isarog’s lizards, frogs, and snakes. Future expeditions
will extend our elevational transects to higher sites in
mossy forests and will circumnavigate the mountain in
an effort to survey drainages other than the one that
encompassed our base in Barangay Panicuason,
Municipality of Naga City on the western slopes of
Mt. Isarog.
For our initial study, we utilized the same transects
and field sites that were studied during earlier investigations of the mountain’s birds and mammals. One of
the goals of the earlier studies was to conduct base
line faunal studies of species’ abundance and distribution along elevational transects within Mt. Isarog
National Park. Wishing to contribute in a meaningful
way to this body of knowledge, we structured our
initial study in a manner that was complimentary to
above: Maps of estimated forest cover on southern
Luzon and adjacent islands in 1880, 1905, 1963
and 1987, showing the loss of old-growth forest.
below: Map of Mt. Isarog showing the boundaries
of the National Park.
opposite page: A misty forest scene in the late
afternoon, following heavy rain at 1150 m.
Isarog’s earlier mammal and bird surveys to allow direct
comparison to the results of these seminal studies. Future
technical and popular publications will accentuate these
comparisons and determine to what degree patterns of
species richness and abundance along elevational gradients differ from those described in birds and mammals.
Arriving at the Mt. Isarog National Park headquarters
in Barangay Panicuason, we were immediately joined by
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Mt. Isarog forest frogs
left from top to bottom:
the Isarog Cloud Frog (Platymantis isarog –
male guarding eggs); the two-spotted tree frog
(Rhacophorus bimaculatus); and the Luzon
stream frog (Rana luzonensis)
below: a “new,” unnamed species of forest
floor litter frog, genus Platymantis
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Mt. Isarog forest lizards
clockwise from top: bark skink (Lipinia pulchella),
bent-toed forest gecko (Cyrtodactylus cf annulatus),
litter skink (Sphenomorphus decipiens), agamid
angle-head lizards (Gonocephalus sp., and
Bronchocela cristatella), and crocodile skink
(Tropidophoris grayi)
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Mt.Isarogforestsnakes
clockwise from left: the rat
snake (Elaphe erythrura),
the Philippine pit viper
(Trimereserus flavomaculatus), a possible new
species of burrowing snake
(Oxyrhabdion cf leporinum),
and a still-unidentified blind
snake (Typhlops sp.)
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local mountain enthusiasts and park
authorities and guided to a base camp
at 450 meters above sea level. From
there, we later extended survey efforts
to 950, 1150, and finally 1350
meters. At these higher evelations,
rainy season precipitation is usually
heavy in the afternoons and evenings,
rendering the forest beautiful, radiant
and green, with a freshly-scrubbed
appearance that is renewed with
every rainfall. It is on these nights,
following heavy rains, that we
experienced some of the most impressive nocturnal congregations of frogs
that any of us have ever witnessed in
the Philippines.
Mt. Isarog’s forests are home to a
remarkable array of frog populations,
each exhibiting distinct ecological
preferences. We recorded frog species
that delivered matings calls only from
high above the ground in the forest
canopy, frogs that called in the forest
understory, several species that called
exclusively from shrubs and herb
layer vegetation, and many species
that preferred the forest floor. In
addition to the newly-discovered Mt.
Isarog cloud frog (Platymantis
isarog, first described by scientists in
1997), we identified at least one and
possibly three new frog species,
completely unknown to science.
Riverside habitats contained populations of a variety of species, most of
which are now only found in clean
forested mountain streams, such as
those that lie within the protective
boundary of Mt. Isarog National
Park. In total, we identified around
15 species of frogs—an impressive
preliminary diversity estimation for a
single site (see Mt. Isarog forest
frogs). We are confident that several
more species await discovery at lower
and higher elevations.
Isarog reptile populations were
equally impressive; in total, we
identified eight species of snakes and
19 species of lizards within the
forested regions of the western slopes
of the mountain. Lizards range in
body size and shape from slender,
delicate species that live only beneath
tree bark, to lugubrious clawed forest
geckos that hang from stream-side
vegetation at night, to colorful and
skittish leaf litter skinks, to hefty
angle-head tree lizards with irritable
dispositions, to secretive, semiaquatic, alligator-like creatures (see
Mt. Isarog forest lizards). We were
particularly pleased to record the
continued presence of the rare Mt.
Isarog forest skink (Sphenomorphus
knollmanae), an endemic Isarog
species that occurs nowhere else in
the world, first described by biologists in 1995. Snakes are harder to
observe, as they are very secretive,
and occur at lower densities in
Suggested reading
Mt. Isarog Protected Area Office. 1999. Istratehiya kan
Pangmanehar sa Bukid Isarog. Protected Area Management
Board (PAMB), Naga City, Philippines.
Balete, D. S. and L. R. Heaney. 1997. Density, biomass,
and movement estimates for murid rodents in mossy forest
on Mt. Isarog, southern Luzon, Philippines. Ecotropica
3:91–100.
Brown, W. C., R. M. Brown, and A. C. Alcala. 1997.
Species of the hazelae group of Platymantis from the
Philippines with descriptions of two new species. Proceedings of the California Academy of Sciences 49:405–421.
Brown, R. M., J. F. Ferner, and L. A. Ruedas. 1995. A
forests, so we consider eight species a
very preliminary account of Isarog’s
snake diversity. The snakes of Mt.
Isarog ranged in shape and color
from spectacularly-colored, deadly pit
vipers, to relatively drab, secretive
burrowing species, to iridescent,
shiny rat snakes, to bizarre, primitive
blind snakes (see Mt. Isarog forest
snakes).
In total, although we are aware that
numerous additional surveys must be
conducted to obtain a reasonable
estimate of the mountain’s herpetological diversity, we were very
pleased with our experience, our data
collection, and our discoveries. We
expect that future surveys will
involve a still greater portion of the
local communities surrounding the
mountain and that our results will
become a valuable addition to the
public record chronicling the
biodiversity of Mt. Isarog National
Park. As we left the quiet forest for
the busy city below, we also shared a
hope that the surrounding communities will continue to cherish Isarog’s
stunning diversity of frogs, lizards,
and snakes—just as they have led the
way to global appreciation of its
colorful and attractive birds and
mammals.
Turn to p. 3 for information about
the research team.
new species of lygosomine lizard (Reptilia; Lacertilia;
Scincidae; Sphenomorphus) from Mt. Isarog, Luzon Island,
Philippines. Proceedings of the Biological Society of
Washington 108:18–28.
Goodman, S. M. and P. C. Gonzales. 1989. The birds of
Mt. Isarog National Park. southern Luzon, Philippines, with
particular reference to altitudinal distribution. Fieldiana
60:1–39.
Heaney, L. R., & J. C. Regalado. 1998. Vanishing
treasures of the Philippine rain forest. The Field Museum,
Chicago. IL, USA.
Heaney, L. R., D. S. Balete, E. A. Rickart, R. C. B.
Utzurrum, and P. C. Gonzales. 1999. Mammalian diversity
on Mount Isarog, a threatened center of endemism on
southern Luzon Island, Philippines. Fieldiana 95:1–62.
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