The jungle stream at night

The next few days were filled with technical details of working in the field and doing lab work in the evening. We got time to call our families at home and eat some nice meals. A highlight was when Heidi and Scott Connelly took Piet and me on a night herping (looking for amphibians and lizards) expedition. I had been taken on a night-time herping expedition in Costa Rica many years before.

The expedition leader on the Costa Rica trip was a professor with lizard-like eyes; they bulged out and he rarely blinked. He carried his cigarettes in one plastic bag tucked under his belt. He had another large bag stuck in the other side of his belt to hold the snakes and frogs he caught on the trip. His plaid polyester pants tucked into the top of his rubber boots and shirt button down polyester shirt, as well as his umbrella, seemed odd at first but his enthusiasm for the animals was contagious. We had a fantastic night tromping through the jungle swamp. He would shine his flashlight and catch the flash of reflective eyes and crash into the swamp after it. He would come back beaming with a poison snake in his hand, or a frog or lizard. First thing the next morning we looked at all our prizes. I jumped at the opportunity to go night herping again.

We secured our headlamps, grabbed our cameras and drove to a local stream as the sun went down. As we walked to the stream Scott and Heidi talked about the incredible diversity of frogs in the region.

In addition to the golden frog are several species of glass frogs. These frogs are clear because they have little pigmentation. You can see their hearts beat by placing a light behind them. They lay their eggs on leaves overhanging the stream where the eggs are less susceptible to egg predators. When the eggs hatch, the tadpoles drop into the stream.

We talked about the tadpoles that live deep in the leaves at the bottom of the streams. Accumulations of leaves on stream bottoms are very low oxygen habitats and the tadpoles have tremendous amounts of hemoglobin (the protein that caries oxygen in our blood and that of other invertebrates). They are bright red when exposed to oxygen. This is a somewhat common adaptation among animals. In temperate lakes, midge larvae known as blood worms inhabit the low-oxygen sediments. They are mostly colorless in their native habitat, but when they are exposed to air at the surface or highly oxygenated water, they turn bright red as their abundant hemoglobin binds all the oxygen it can.

Panama has 195 documented species of amphibians. This is over half the number found in the US in a country slightly smaller than the state of South Carolina. Thirty four of these species are found nowhere else (are endemic) and most are restricted to Central America. Panama is an amphibian-lovers paradise and El Valle has historically been a Mecca for people wanting to see Panamanian frogs and other amphibians. Frog societies plan meetings and collecting trips commonly with El Valle as their base of operations.

During the day, brightly colored toxic frogs such as poison dart frogs are common. These frogs practically glow in the low light of the tropical forest. Their bright colors are a signal to predators that says “I am poison, eat me and you die”. Other species, also brightly colored, look like poisonous species, sending the same signal to predators, but are not toxic. This mimicry allows the frogs to avoid predation without having to synthesize costly toxic chemicals. The two types of frogs are balanced in population numbers, because if there are too many of the non-toxic species, predators will start eating and frog with that coloration. So, the non toxic frogs take advantage of the toxic species that they mimic. Evolution has lead to some amazing things, and “cheaters” are a fact of life!

At night the more cryptically colored frogs come out to forage. Their calls filled the stream bottom as we worked our way up the rocky stream channel in the dark. Our flashlights were reflected by the eyes of freshwater shrimps as long as your hand. These shrimp are very skittish, and they scuttled out of sight under rocks by the time we were within 50 feet. Freshwater shrimp are common in tropical streams. Some species have been taken into captivity for aquaculture, particularly in south-east asia. Some of these shrimp play the part that crayfish (crawdads) fill in more temperate streams (omnivores), but others specialize on fine or coarse particles, or algae, or other food types. The shrimp are most common in smaller streams where large predatory fish will not eat them.

Moths bigger than my hand were hanging over the stream. We saw an occasional snake foraging through the underbrush near the edge of the stream; preying on the abundant frogs. The jungle shows a whole different face at night, animals scurry off through the darkness, bats dart around over the stream, and there are spiders the size of a salad plate with eyes that glow in the darkness when your flashlight happens to strike them. Scott and Heidi discussed how the frogs probably would not be around the next time I came back. We left the stream to get back to our hotel muddy, sweaty from our walk, and thoughtful.