Volunteers and Visitors

Treefrog Breeding Frenzy!

Cesar Barrio-Amoros holds a PhD in biology and is a notable taxonomist, herpetologist, author, and photographer. Following his experience in the Osa, reflected below, Cesar has planned to lead a reptile and amphibian workshop at Piro Biological Station next May or June, the beginning of the wet season.

I have traveled throughout most of Latin America in search of amazing herping spectacles. In the Galapagos, I saw marine iguanas (Amblyrhynchus cristatus) and Galapagos giant tortoises (Chelonoidis nigra). I witnessed an astonishing diversity of poison frogs in Peru and made some interesting scientific discoveries on the Tepuis of Venezuela. My curiosity has now led me to one of the tiniest countries: Costa Rica. Here, the herpetological diversity is bewildering and vibrant. Due to Costa Rica’s intense biodiversity, it is not difficult for a photographer to capture nearly all of the herping species in a matter of years.

DSC03038

The gliding treefrog (Agalychnis spurrelli) was on the top of my herping list after learning about it on a BBC documentary. I have actually seen the individual species in the Caribbean and Pacific lowlands. However, I never saw one of those impressive reproductive aggregations where thousands of frogs gather in a pond and lay millions of eggs in just a few nights.

I was envious of the photographs my colleague, Manuel Sanchez, captured while working at Osa Conservation’s Piro Biological Station in the Osa Peninsula. I immediately scheduled a visit to see the event. When I arrived, Manuel informed me that the area was full of frogs, thousands were laying eggs in amplexus (amplectant pairs).

Around 6:00AM the next morning, we left for our journey along with herpetologist intern and researcher, Michelle Thompson. At the site, we noticed some bushes moving and, upon further investigation, realized there were a few frogs still laying eggs. The great wave was the previous night so only about 10% frogs remained.

DSC03074

Still, it was a breathtaking sight because they were completely surrounded by millions of eggs! Michelle and I were amazed — this was quite an experience for a herpetologist. Next time, I need to arrive a few days in advance in order to catch the whole spectacle!

Science and Research, Volunteers and Visitors

Golfo Dulce Poison Dart Frogs

Submitted by Steven Waldron; Seattle, WA

Twenty years ago, I backpacked and hiked along the wild beaches and coastal rainforests of the Osa peninsula and became acquainted with some of the fantastic wildlife that the region is well-known for. Near the Sirena station at Corcovado National Park, I became intimate with the loud squawks of Scarlet Macaws sailing overhead, the crash of surprised tapirs bolting through the forest, and the pre-dawn chorus of Howler monkeys. One of the sensory aspects I appreciate most about exploring this region is the rich array of sounds that greets the rainforest naturalist. The forests of the Osa are alive with every kind of exotic screech, hoot, cry, whistle and howl. However, there was one voice that alluded me during that first trip many years ago; that of a little poison dart frog unique to the region, Phyllobates vittatus, the Golfo Dulce poison dart frog. Though the call of Phyllobates vittatus was certainly in the mix of the rainforest cacophony that greeted me back then, I just didn’t know how to identify it and discover its secrets within the complex mystery of the jungle matrix. On a recent trip to the Cabo Matapalo region, I was focused on encountering this beautiful red/black/green jewel of a frog and to document some of its natural history and beauty in photos.

From my research, I knew that Phyllobates vittatus is endemic to southwestern Costa Rica and found from Domincal in the north to (likely) the Boruca peninsula in the south. Due to its limited distribution, P. vittatus is listed by the IUCN as an endangered species. P. vittatus is known to inhabit primary forest microhabitats near streams; it’s diurnal and dwells in the leaf litter of the forest understory. Phyllobates vittatus is one of the true poison dart frogs with another sister species found in the Caribbean slope of Costa Rica and Panama (Phyllobates lugubris) and three other known relative species in the Chocó rainforest of Colombia (Phyllobates aurotaenia, Phyllobates bicolor and Phyllobates terribilis). The evolutionary links to the Chocó appear to be a common theme in Osa natural history.

19881843978_7859cdbac4_oDuring our first day in the Matapalo forest, my wife and I went for a late afternoon walk along a perennial creek with a rocky stream bed covered in fallen leaves. It seemed like the ideal habitat for Phyllobates vitiates, and it was! My wife found our first Phyllobates vittatus hanging out in a sheltered spot below a fallen log. Interestingly, I found this very frog in the same spot during my informal surveys over the course of the next week. P. vittatus appears to be fairly territorial in its habits. As the night was approaching quickly, my wife and I decided to resume our Phyllobates search for the following morning. A few hours after the next dawn, we were rewarded with the discovery of several vocalizing males singing from the creek banks. Luckily, I was able to photograph the frogs in their microhabitat and witnessed several courting male/female pairs.

Despite their toxic nature and bold coloration, P. vittatus is a fairly shy frog that is more often heard than seen. Once you learn the song of this frog, you realize that they are locally abundant in the Osa forests. However, the calling males will usually quickly fall silent and retreat into rock crevices or leaf litter when they feel threatened or discovered. Without this interruption, the typical reproduction process would proceed as follow:

The male P. vittatus serenades the female as she looks on. If all goes well, and both parties are mutually interested, the pair will retire to a sheltered spot in the fallen leaves where they will lay 7 to 21 eggs. The eggs will hatch in a couple of weeks; during that time period the male will periodically return to the developing embryos and moisten them with water shed from a specialized patch of vascularized tissue on his posterior. When the tadpoles hatch, they will then be visited by their father, climb onto his back and he will hop off into the forest to find a small pool of water for them to complete their development into little frogs some forty-five days later.

As our days of birding, botanizing and frogging unfolded during our relaxing week in Cabo Matapalo, the song of Phyllobates vittatus was a constant companion as it greeted us cheerfully from nearly every creek, spring and stream bed along the forest trails we visited. I came to look forward to hearing it as much as I enjoyed the raucous call of the macaws, the screech of the parakeets, the complaints of monkeys and the crashing of waves along the wild beaches. I realized that Phyllobates vittatus presence in these forests is a small but critical voice in the rich tapestry of biodiversity that gives southwestern Costa Rica its unique and charming character.