Alien Earthlings

in Drake Bay, Costa Rica

 

 

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Frogs Home Page

Order: Anura

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.Gaudy Leaf Frog - Agalychnis callidryas 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.Splendid Leaf Frog - Agalychnis calcarifer 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!

Frog diversity is at it's grandest in the Tropics and reaches its zenith in the rainforest.Hourglass Tree Frog - Dendropsophus ebraccatus 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.

By far, the most amazing thing about frogs is their lifestyle. You probably learned that frogs lay their eggs in a river or pond.Masked Tree Frog - Smilisca phaeota 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.

Pygmy Rain Frog - Pristimantis ridensOther 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.

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 pulveratum) 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. Strawberry Poison-dart Frog - Oophaga pumilioAfter 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. Parachuting Leaf Frog - Agalychnis saltator

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.

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.

Granular Glass Frog - Cochranella granulosaCurrently, 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.

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. Gliding Leaf Frog - Agalychnis spurrelliOnly 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

The Frog Files

Frogs Home Page

Common Rain Frog - Craugastor fitzingeri

Gaufy Leaf Frog - Agalychnis callidryas

Gladiator Tree Frog - Hypsiboas rosenbergi

Glass Frogs Home Page

Emerald Glass Frog - Centrolenella prosobleponCascade Glass Frog - Cochranella albomaculataGranular Glass Frog - Cochranella granulosaCricket Glass Frog - Hyalinobatrachium colymbiphyllumDusty Glass Frog - Hyalinobatrachium pulveratumReticulated Glass Frog - Hyalinobatrachium valerioi

Gliding Leaf Frog - Agalychnis spurrelli

Hourglass Tree Frog - Dendropsophus ebraccatus

Giant Marine Toad - Bufo marinus

Masked Tree Frog - Smilisca phaeota

Smoky Jungle Frog - Leptodactylus petadactylus

Tink Frog - Diasporus diastema

Salamanders - Order: Caudata

 

 

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