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One
excellent
reason to visit Costa Rica during the rainy months is to enjoy our
rich variety of frog species. Many are graced with strikingly
colorful patterns, others are cryptic and blend into their
surroundings perfectly.
They range in size from incredibly
delicate glass frogs to huge voracious Smoky Jungle Frogs, capable of turning the tables on
unsuspecting snakes up to a foot and a
half in length.
There is certainly great variety among Costa Rica's
frog species, but, almost invariably, frogs have a permanent smile
and large, engaging eyes. At a glance they seem quite friendly and
curious, almost comical, as they inspect you inspecting them. As a
photographer, I love photographing frogs. They are charming and simply make wonderful
subjects.
Perhaps legendary turtle conservationist
Archie Carr says it best in his book The Windward Road: "I
have always liked frogs. I liked them before I ever took up zoology
as a profession; and nothing I have had to learn about them since
has marred the attachment. I like the looks of frogs, and their
outlook, and especially the way they get together in wet places and
sing about sex." There certainly is something entirely
endearing about frogs. The following web pages pay tribute to some
of these amazing little creatures who make so many of our Night
Tours so special, at times unforgettable. |
Frogs are the most diverse
and successful group of amphibians. There are approximately 4400
identified species worldwide and they inhabit every continent except
Antarctica. Frogs have managed to adapt to even the most
inhospitable climates.
Some frogs live in the desert and burrow into the earth
entering a type of hibernation for most of the year. When the rains
come, they emerge from their slumber to breed in the temporary pools
formed by the rainstorms.
At the other extreme, there
is a frog which ranges into Alaska that freezes during the winter,
only to thaw out in spring to reproduce once conditions are
favorable. You could literally put this frog in your freezer for
months, then take him out, let him thaw and watch him hop away!!
Talk about resilience!
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Frog diversity is at it's grandest in the Tropics and reaches its
zenith in the rainforest.
There are approximately 130 frog species in Costa Rica and they
inhabit almost every conceivable habitat. From lowland marshes to
mountain treetops. Despite their relative abundance throughout the
country, seeing these magnificent creatures in the wild requires
some effort and, as with every nature encounter, a bit of luck.
Many of our guests comment that before The Night Tour they had not
seen any frogs on their Costa Rican travels. Most frogs are
nocturnal and their activity peaks on rainy or very humid nights.
Even frogs that are active during the day, like Poison-dart Frogs,
are elusive and shy. The frogs' call, which is unique to each
species, is usually a good way to locate and identify them.
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By far, the most amazing thing about frogs is their lifestyle. You
probably learned that frogs lay their eggs in a river or pond.
A tadpole then hatches out
and develops in this aquatic environment until it turns into a frog.
This pattern is shattered in the tropics.
Scientists have documented
about thirty-five variations in the reproductive patterns of frogs
and toads worldwide, fifteen of which occur in Costa Rica. Some of
these patterns test the boundaries of the
imagination and border on the bizarre.
As Adrian Forsyth and Ken Miyata write in their
wonderful publication Tropical Nature: "Some Neotropical
frogs will stretch your credulity beyond its limit, resembling as
they do the creations of an alien biology." |
The Marsupial Tree Frog (Gastrotheca
cornuta) is one such variation that defies belief. These
remarkable frogs, which are found on the Caribbean Slope of Costa
Rica, lead their lives in the highest reaches of the forest canopy.
When they mate, the female will catch her fertilized eggs with her
feet as she lays them and slip the eggs into a pouch on her back!
The embryos will go through direct development in this pouch,
bypassing a free swimming tadpole stage, and the little froglets
will emerge from the pouch fully formed.
Other
tropical frogs will go through
direct development inside the egg, in some species with a parent
guarding the egg clutch. Once their metamorphosis is completed tiny,
fully formed, froglets emerge from the eggs. Two of these frogs, the Common Rain Frog (Craugastor
fitzingeri) and the
Common Tink Frog (Diasporus diastema), are featured on
this website.
One incredible variation is
Eleutherodactylus jasperi, from Puerto Rico. In this case,
fertilization was internal and the female kept the eggs inside her
oviduct. When the little frogs hatched she would give live birth. I
use the past tense because this frog hasn't been seen since the
1980's and is currently believed to be extinct.
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Amazing parental care is part of the reproductive cycle of some
Glass Frogs in the Hyalinobatrachium genus, especially
the Reticulated Glass Frog (Hyalinobatrachium valerioi).
In this case, the male parent will guard his egg clutches 24 hours per
day. The male Cricket Glass Frog (Hyalinobatrachium
colymbiphyllum) guards his eggs through the night but abandons
them during the day. But, perhaps the parents most dedicated to their offspring are some
members of the Poison-dart frog family, particularly the Strawberry Poison-dart Frog (Oophaga
pumilio) and the Granular Poison-dart Frog (Oophaga
granuliferus).
With these tiny frogs egg laying generally takes place on the
ground, where three to five eggs are laid. The father will then
guard the egg clutch, hydrating it occasionally to avoid
desiccation.
After the eggs hatch, the female returns to the site
and carries the tadpoles to water, normally in the tank of a
bromeliad. She places each individual tadpole in its own tank to
avoid competition among siblings. What follows is an
example of parental care unrivaled amongst the world's amphibians. The mother will
actually return to each tadpole's tank periodically and feed them
unfertilized eggs!! Motherly love at its finest. The generic name
for this species,
Oophagus, literally means "egg eaters". |
But
perhaps the most incredible reproductive pattern of any frog species
is that of Australia's endemic Gastric Brooding Frogs. The Gastric
Brooding Frog (Rheobatracus silus) and the Northern Gastric
Brooding Frog (Rheobatracus vitellinus) were only discovered
in 1972 and 1984 respectively. It remains unknown whether the female
swallowed her fertilized eggs after mating or her tadpoles after
hatching, but all the tadpole's development took place inside the
mother's stomach! Their development took about eight weeks and the
mother could shut off her stomach acids and did not feed for the
duration.

She could
hold up to thirty young in her stomach at one
time. The stomach, swollen with tadpoles, would get so large it
would take up most of her body cavity and her lungs would be unable
to fully inflate! When the froglets completed their metamorphosis,
the mother would open her mouth wide and they would emerge through
her mouth! Sadly, these frogs went the way of so many other species
and are now believed to be extinct. The Gastric Brooding Frog was
last seen in September 1981 and the Northern Gastric Brooding Frog
was last seen in March 1985, only one year after it was discovered
by scientists.
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Worldwide
amphibians are in crisis and extinction seems to be a troubling
trend. It is estimated that about 25 percent of the world's frog
species are currently endangered. Theories about the causes are as
abundant as they are varied. Pollution, global warming, acid rain,
the depletion of the ozone layer, destruction of habitat, and the
introduction of invasive species have all been suggested and all
probably contribute to the decline of amphibian populations.
Currently, scientists seem to agree that one of the
mayor problems facing amphibian populations is a Chytrid Fungus
discovered in 1999 called Batrachochytrium dendrobatidis.
This fungus is believed to have spread from South Africa throughout
the world via the commercial trade of the African Clawed Frog (Xenopus)
which began in the 1930's. The fungus causes a disease called chytridiomycosis which is often fatal.
It thrives in cool, humid
environments and can be expected to affect fifty percent of an
infected area's amphibian species, wiping out eighty percent of the
population of each affected species. Its rate of progression
in Central America has been calculated at 28 to 100 kilometers per
year and has been devastating.
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During the late eighties, Costa Rica's Monteverde Cloud Forest lost
20 out of 50 frog and toad species, including the beautiful and
endemic Golden Toad (Bufo periglenes). Other Cloud Forests throughout the
country, including Braulio Carrillo National Park, have also been
affected. The endemic Hyla xanthosticta is believed to have
been lost to this invasive fungus in Braulio Carrillo National Park,
along with most of the other frogs there.

Only one specimen of this
once rare species was ever collected on the southern slope of Volcan
Barva. Australia's Gastric Brooding Frogs are believed to have
fallen victim to this predator and countless others are in danger of
suffering the same fate.
The sharp
decline in amphibian population should serve as our miner's canary
and should not be taken lightly. As conditions on earth deteriorate
due to pollution, depleting resources, deforestation and an ever
increasing human population, it is these sensitive species that will
be the first to disappear. By doing so, they are crying out a
warning to all of humanity. They are begging us to respect all other
species and allow their coexistence - to take care of our planet, which
is our only home. They remind us that humans are not immune to
extinction and that extinction is forever. |
References:
Beletsky, L.
2005 Travellers' Wildlife Guides Costa Rica
Interlink Publishing
Brem, F.
Lips, K. Mendelson J.
Field-Sampling Protocol for Batrachochytrium
dendrobatidis from living amphibians, using alcohol
preserved swabs.
Available from
http://www.amphibianark.org/chytrid.htm
Carr, A.
1955, 1979 The Windward Road The Florida State
University Press
Forsyth, A. 1990 Portraits of the Rainforest
Camden House Publishing
Forsyth, A. & Miyata K. Tropical Nature
Touchstone / Simon & Schuster
Janzen, D. 1983 Costa Rican Natural History
University of Chicago Press
Leenders, T.
2001 A Guide to Amphibians and Reptiles of Costa Rica
Zona Tropical
Savage, J. 2002 The Amphibians and Reptiles of
Costa Rica University of Chicago Press
Weldon C, du
Preez LH, Hyatt AD, Muller R, Speare R. Origin of the
amphibian chytrid fungus. Emerg Infect Dis [serial on the
Internet]. 2004 Dec [date cited]. Available from
http://www.cdc.gov/ncidod/EID/vol10no12/03-0804.htm
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The Frog
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