Frogs Of The Osa Peninsula

Red-eyed tree frog (Agalychnis callidryas), Osa Peninsula, Costa Rica. Working in the dark, I made a series of images with my DSLR handheld and a softbox-diffused flash mounted on-camera. Nikon D3X, 200mm ƒ/4 Micro-Nikkor lens, Nikon SB-900 flash, LumiQuest softbox.

My foot plunged through cool rushing water to find the firm purchase of a pebbled streambed. The shallow creek that emerged from beneath an arch of lush jungle foliage was both beckoning and mysterious, and upstream we went, with the sound of Pacific Ocean waves pounding the wild beach behind us. “You watch the left bank, and I’ll watch the right,” said my companion, Belgian-born naturalist Rinaldo Mulder. After a few minutes of wading, he calmly motioned me over to some damp leaf litter beside a moss-covered log. “There she is,” he whispered.

Mulder’s eagle eyes had located the tiny rain-forest denizen that we were looking for, Phyllobates vittatus—a Golfo Dulce poison dart frog. About an inch long and glossy black with striking orange and turquoise markings, she blended perfectly against the wet reflections and dark tones of the decomposing leaves that were her home. A single quick hop had announced her presence.

While Mulder kept an eye on the frog, I spread my tripod low and mounted my standard macro rig—a Nikon D3X and 200mm Micro-Nikkor lens. An off-camera softbox provided illumination in the subdued light under the rain-forest canopy. My heartbeat quickened as I moved in close and peered through the viewfinder. The fragile little creature was transformed into a formidable predator. How very fortunate I was to be so close to this creature in its native habitat—a primeval rain forest at the southern tip of the Osa National Wildlife Refuge on Costa Rica’s Pacific coast. Over the next several days of exploration and discovery, I would be reminded again and again of just how special this place is.

It’s hardly a coincidence that I had selected the Osa Peninsula for a project on tropical amphibians. Around the world, amphibian habitats and populations are experiencing rapid decline, and throughout the tropics, the ecosystems that host the greatest amphibian biodiversity often face the greatest threats. From Borneo to Brazil to Madagascar, climate change, deforestation, agricultural expansion, pollution and the fungal disease chytridiomycosis have combined to take a terrible toll, leaving almost a third of all known amphibian species listed as “threatened”—or worse—on the Red List maintained by the International Union for Conservation of Nature (IUCN). Our little friend, the endemic Golfo Dulce poison dart frog, is listed as “endangered,” but on the Osa, dozens of native amphibian species seem to be thriving.

Home to 2.5% of all known species of life on Earth and more than half of all animal and plant species present in Costa Rica, the Osa Peninsula offers a shining example of conservation success through sustainable ecological stewardship. The Osa National Wildlife Refuge, an ingenious 4,260-acre land management program established as a partnership of private landowners and the Costa Rican government, is part of a contiguous 15,000-acre ecological corridor preserving an area the size of Manhattan south of the Corcovado National Park boundary all the way to the tip of the peninsula. Since its establishment in 1999, the refuge has focused on conservation and ecotourism with a small environmental footprint, simultaneously serving the economic interests of the local community and the health of the ecosystem itself.

More than 20 individual properties make up the Osa National Wildlife Refuge, most of which were bought up in the 1980s and 1990s specifically for the conservation of this important biological
corridor. For the most part, these are entirely undeveloped, handed over by the owners for ecological management by Conservación Osa, the local conservation organization. Two refuge properties are ecotourism businesses, including El Remanso, a 150-acre parcel of primary-growth rain forest running from a ridgetop 350 feet above sea level all the way down to the pristine beach. The sloping forested landscape funnels rainwater into creeks that drop precipitously over stunning waterfalls into fern-rimmed pools. A lagoon just off the beach is home to a shy, six-foot spectacled caiman. Blending in perfectly with its remarkable setting, the lodge at El Remanso has a tiny ecological footprint by design. Totally off the grid, its electricity is generated by a micro-hydro facility and solar panels. Of its waste, 92% is recycled or composted. These behind-the-scenes efficiencies go largely unnoticed by guests, who experience stylish accommodations and a welcoming atmosphere more like a reunion of old friends than anything else.

Amphibians are often referred to as the canaries of the ecological coalmine—important indicators of environmental health. Herpetologists are quick to note that scientific research on Osa amphibian populations is lacking. According to Dr. Bill Lamar of the University of Texas, most studies in the area have focused on “identification and range as opposed to abundance and ecology.” Dr. Lamar adds that the numerous local microclimates make thorough study of amphibian populations challenging. “One of the problems is that there are distinct areas on the Osa and the adjacent mainland, at least in terms of humidity,” he says.

This lack of detailed research makes it difficult to determine exactly how global warming and climate change—experienced so far as wetter rainy seasons and warmer, drier dry seasons—will impact amphibians here in the long term. Mulder points out that changing weather patterns will likely have mixed effects: “More rain during the wet season could be good for some frogs, but higher peak levels in the creeks would also wash out the leaf litter on the banks, and that’s exactly the environment that Golfo Dulce poison dart frogs need to reproduce.”

Over the last two decades, however, the experiences of local naturalists and visiting biologists suggest that population trends tend to be stable so far and may be increasing in some areas, particularly in secondary-growth forest that has been provided the protection it needs to recover.

Granular glass frog tadpoles (Cochranella granulosa) develop inside an egg case. I set up my tripod in the water and used an off-camera flash in a softball, illuminating the egg mass from below. Nikon D3X, 200mm ƒ/4 Micro-Nikkor lens, Nikon SB-900 flash, LumiQuest softbox.

Since the creation of the Osa refuge, a number of key threats that impact frog populations around the world have been locally eliminated or kept in check. Non-native species that might out-compete or prey upon native amphibians have yet to become a problem. The practice of poaching for the international exotic pet trade, once common, appears to have been reduced dramatically with the creation of new laws protecting wildlife and greater awareness of the economic value of local biodiversity. Commercial logging has ended within the refuge. The absence of mining or significant agriculture has left the surface water free of heavy metals or pesticides. Elsewhere, runoff of agricultural fertilizer and livestock waste into rivers and lakes leads to algae blooms and a resulting explosion in populations of aquatic snails that are a key vector for trematode worms responsible for debilitating deformities in frogs.

The Osa frogs obviously benefit from the health of the ecosystem, in general, but Conservación Osa and local land owners also have taken measures to encourage favorable conditions. “My impression is that we’ve been seeing greater numbers and diversity of amphibians at El Remanso in part due to various practices we’ve put in place,” says Daniel Gehring, who has landscaped the area around the lodge with native plants favorable to the frogs and has created a small frog pond. Of course, the healthy rain-forest ecosystem does the bulk of the work, and for any visitor here it’s an inescapable fact that the frog species are present in great abundance.

Within two days of my first outing with Rinaldo Mulder, I had encountered a dozen different frog species on my walks through the forest. Within five days, I had found 15 Golfo Dulce poison dart frogs on the banks of the creeks.

“We used to see them only in one particular spot, but now we find them at various locations in several creeks,” says Mulder. He added that a biologist who visited recently managed to document 30 different amphibian species during a single nighttime walk. Some of the native species include the “gaudy” red-eyed tree frog, masked tree frog, gladiator tree frog, cane toad, rain frog, glass frog and two more species of colorful poison dart frog—the green-and-black and the granular, the latter of which is often described as a red frog wearing green tights. By the way, poison dart frogs don’t bite and are perfectly safe to photograph up close, but you wouldn’t want to lick one.

Considering the wild nature of the landscape, access for photographers is very good indeed. Well-maintained trails lead through the forest to old-growth trees, creeks, waterfalls and beaches. Observation platforms high in the forest canopy provide an unusual vantage point, and the restaurant deck at El Remanso is a superb wildlife-viewing platform, overlooking fruiting trees that attract macaws, toucans and monkeys. It’s a good idea to bring a long lens to breakfast.

Green-and-black poison dart frog (Dendrobates auratus). This female green-and-black was a little over an inch long. I set up my tripod spread low to the ground and placed the flash in a softbox to create this image in the dark conditions under the rain-forest canopy. Nikon D3X, 200mm ƒ/4 Micro-Nikkor lens, Nikon SB-900 flash, LumiQuest softbox.

In fact, after a rain is the perfect time to go looking for frogs. In addition to the Golfo Dulce and granular poison dart frogs that are most easily found in the leaf litter along the creek banks, the semi-arboreal green-and-black poison dart frogs can best be found as they traverse the ground when moving from tree to tree. The various tree frog species tend to find a perfectly camouflaged position to lay low and sleep during the day, becoming active as the sun goes down. They can be found by homing in on their distinctive calls, aided by a headlamp once close. The photogenic red-eyed tree frog is commonly found on vegetation near the El Remanso pool, perfect for a pre-dinner shoot. At night, it’s often easiest to photograph handheld with flash, freezing subject and camera motion with the quick strobe. A softbox, handheld or on a flash bracket, can be positioned just out of frame for soft, even lighting.

Logistically, a visit to the Osa is an exotic adventure balanced with surprising convenience. The Costa Rican capital of San José is a short hop from the U.S., and the quick puddle-jumper flight over the mountains and along the coast to Puerto Jiménez is spectacular. From there, visitors can rent a vehicle (4WD is recommended), arrange ground transfers with their lodging or hire a local taxi. The unpaved road to El Remanso fords three small rivers and passes through areas that are perfect for photographing monkeys as they cross in the low canopy overhead. Once deep in the rain forest, one can’t help but feel very, very far away from all.

Next time, I’ll be in search of glass frogs. Semi-transparent, they’ve evolved greenish bones as part of their impressive camouflage. I’ve heard their distinctive high-pitched chirps all around me in the jungle, and I’ve photographed their tadpoles developing inside transparent egg cases clinging to leaves above a creek, but so far adults have eluded me. In the Osa, there’s always something new to discover. Let’s hope it stays that way.

Justin Black

Justin Black's photographs have been published widely and featured in numerous exhibitions around the U.S. and abroad, from the UK and Germany to Los Angeles and the United States Capitol. Formerly executive director of the International League of Conservation Photographers (ILCP), Black has contributed photography in support of conservation campaigns to protect threatened landscapes and ecosystems from British Columbia to Brazil, and from California’s Sierra Nevada to the Chesapeake Bay watershed. His company, Visionary Wild, has achieved a reputation for delivering world-class photography travel and education experiences for passionate photographers with leading professional instructors.