Pura Vida 3: Swamp Froggin

Amphibians are intrinsically linked to water. When reproducing, amphibians lay eggs in water or moist microhabitats to prevent them from drying out. After a period of development, the eggs hatch out into the surrounding water as free swimming, gilled larvae. However, many amphibians circumvent this pattern in some unusual but fantastic ways. Amphibians also have moist skin that passively transports water in and out of their body. In particular, a highly vascularized patch ventral to the pelvis is important in the osmotic regulation of amphibians.

Because the wet tropical forests of La Selva Biological Station receive around 4 meters of annual rainfall, they harbor an impressive diversity of amphibian life with at least 48 species documented. On rainy or humid nights, many amphibians can be found out in the forest or breeding in areas with standing water. These swamps provide excellent grounds for amphibians to reproduce as they lack some predators, such as fish.

On my first night at La Selva, a few students and I trekked out into the rain to investigate the swamp near our rooms. This “suampo” is called the “cantarana,” which literally means “singing frog.” It has a wonderful boardwalk that cuts directly through the swamp, which is excellent for viewing animals that would otherwise be difficult to see. It was raining steadily, and we were amazed by the number of animals we saw and heard. I became captivated with the swamp herpetofauna and explored numerous swamps spread across the property. The Cantarana, Suampo Experimental, and Chanchera became my nightly stomping grounds.

Common in and around the swamps is the Smokey mountain jungle frog (Leptodactylus pentadactylus). This is a large frog found perched near the water’s edge on the ground or on logs. These voracious predators (eat anything smaller than themselves) can often be spotted at night by their red eye shin in the light of a headlamp. This species lays its egg in large foam nests in dry cavities. Subsequent rain then fills up the cavities, releasing the tadpoles to ephemeral water sources. Although I never experienced it, I hear that if you pick an adult L. pentadactylus up they sometime will emit a large squeak/squeal sound. Unfortunately, I did make the mistake of rubbing my eye after holding a particularly large individual. I proceeded to feel immense discomfort and pain in that eye for the next hour. Looking back, this was a foolish thing to do, knowing that all amphibians have toxic skin secretions to some degree.

Leptodactylus pentadactylus

Another extremely common swamp frog is Lithobates vaillanti. This large green or brown member of the family Ranidae will perch on logs or mud banks. Seems like a likely food source of the resident caiman….

Lithobates vaillanti

On rainy nights, many frogs of the family Hylidae breed in the swamps. Hourglass tree frogs (Dendropsophus ebraccatus) can be found perched among various understory plants. These are beautiful hylids with a highly variable pattern on their back that can resemble an hourglass in shape. Similarly, Dendropsophus phlebodes can be found breeding during rainy nights. In my experience, this species is less common, as I found only two in ten weeks, as opposed to many D. ebraccatus (>50). A friend of mine was studying the ecological differences between these two sympatric congeneric species. He found interesting differences in the insects they consume and the structures they perch on.

Dendropsophus ebraccatus

Dendropsophus phlebodes

One charismatic species that I became exceptionally fond of was the Scarlet-webbed tree frog (Hypsiboas rufitellus). This gorgeous swamp hylid is unique for having bright red webbing between its toes. Calling males can have a blue throat which is quite pretty. I have seen yellow, green, and grey individuals.

Hypsiboas rufitellus

Two species of the genus Scinax can be found in the swamps of LSBS. Scinax elaeochrous is a beautiful yellow hylid. It is readily identified by its visibly green bones. It is a fairly common frog found breeding in numbers during rainstorms or out to a lesser degree on a nightly basis. When held, this species emits a foul stench. On the other hand, Scinax boulengeri is more elusive, only showing itself during breeding events. This species has large tubercles distributed across the body, creating an interesting contour, and an elongate snout. Although primarily a drab brown/grey coloration, there are bold spots of yellow, orange, and green on the groin and the back of the thigh.

Scinax elaeochrous

Scinax boulengeri

Another species that I did not see often was Tlalacohyla loquax. On my first night, I observed and photographed an amplectic breeding pair. I did not identify another until one of my last nights in La Selva; unfortunately, this individual evaded photographs. This species is larger than most of the other hylids, yellow, and lacking bold patterns.

Tlalacohyla loquax

I’ll end this segment with the perhaps the most recognizable of anurans, the Red-eyed tree frogs (Agalychnis callidryas and A. saltator). These charismatic frogs are a national symbol of Costa Rica’s wonderful animals and forests. Active nocturnally, these canopy dwelling species descend down to the understory to breed explosively during the heaviest rain events of the rainy season. Unlike many frogs that lay eggs directly in water, these species oviposit onto leaves hanging over water. After a period of development, the tadpoles emerge and fall through the air into their new aquatic home. A. callidryas has a barred blue pattern on the flanks, while A. saltator has creamy blue flanks with no pattern.

Agalychnis callidryas

Agalychnis saltator