Herp Haunts of the Peruvian Amazon (by Brian Crnobrna, Herp Team Coordinator)
2 September 2010
To answer the most simple of questions regarding Amazon herping, I want to use this blog to outline all the places one should look in order to find reptiles and amphibians in this diverse and challenging ecosystem. It is the most common question I receive, since many people are understandably overwhelmed by the rainforest habitat, and despite all the things that appear before them they don’t know which ones they should concentrate on in order to see a herp.
My most likely first answer will be “the surface of living leaves,” which isn’t a very helpful answer considering how many leaves there are, but it’s true. The best way to herp in the Amazon is to go out at night and throw some light on nearby leaves, the ones that are up off the ground in the understory region of the forest. In this way you’ll find some frogs before too long. When I say “the surfaces of leaves” I could try and be a bit more specific, but there might not be much more to this trick. Leaves that have a smooth surface on top, free of hairs or spines meant to drive off invaders, are the best, and big round ones are the most visible. Sometimes the frog sits in the middle of the leaf, where it may take a water conservation posture that makes it look like a green blob, especially during the day. Or it may be situated more towards the base of the leaf where stability is greatest; depending on what the frog is doing at the time. You can observe enough bugs on leaf surfaces to make a strong argument that the frog is hunting when it’s sitting in the middle of a leaf. However, a couple other options are that it’s thermoregulating–that the particular microclimate and temperature of the leaf is providing the frog with the heat is needs–or that is in reproductive behaviour–that the leaf is giving the frog a good position to broadcast its call far and wide.
Tree frogs of the genus Dendropsophus are what you’re likely to see in this way, and in so doing you’ll be taking stock of most of the amphibian species in the forest, when you include the occasional rain frog, toad, or monkey frog that shares the habit. Additionally, you will occasionally encounter a lizard or snake on a leaf at night. These are a certain subsection of species, which sleep in seemingly obvious places. Predator avoidance is the leading theory on why this is. Also, the abrupt loss of heat from the setting sun may leave some lizards out cold and needing to sleep on random leaves. Here, they are ideal prey for one of the most common snakes in the forest: Imantodes cenchoa, the Blunt-headed tree snake. Look for these and other snake species sprawled out between branches or weaving their way up trunks or vines.
The way a snake gets from the ground to the canopy in a forest is illustrative of the interconnectivity of the habitat. In observing such animals you can see how the forest structure gives way to varied microhabitats that may all contain different species. Going beyond the first set of leaves presented to you, it’s easy to spot a large Osteocephalus tree frog as it uses its astonishing agility to run up a palm trunk and into the canopy. During the day on the trunks of larger trees you may find lizards like Plica plica aka "Tree runner" that have a specific microhabitat preference for such spaces. Beyond that though, in the main canopy of the forest itself you’ll be hard-pressed to find anything without climbing gear. Not only are things too far up, they often have cryptic colouration such that viewing them from below makes them wash out against the sky, and viewing them from above makes them blend in with the ground. This is the “bicoloured” strategy of species like Phyllomedusa palliata and the beautiful Xenoxybelis vine snake, which adds another green level to its colour pattern so it can hide in vines and leaves as well.
Ground-dwelling herp species range from the large Whiptail lizards (such as Ameiva ameiva) that run across the ground, to frogs that hop around the leaf litter, to the small specialized frogs and lizards that spend time just underneath the litter layer and just out of sight, to the snakes and other bizarre creatures that freely travel below the soil surface and are termed fossorial. These animals will always be able to survive better in areas where the leaf litter is thick and full of prey, like ants, termites, and small crickets. But they will always be easier to see in areas where the leaf litter is sparse and they can’t hide as easily. There may be more to this, since I regularly observe animals laying on bare soil both on and off trials. Even animals that make their living in the leaf litter will occasionally reach their peak active temperature, after warming up and eating their fill of insects. At this point, they may just as well seek out cooler environments like bare soil or puddles. This is why I always search areas of bare soil, not only because they may attract overheated herps, but also because they often are a sign of invertebrate activity–the prey source of most reptiles and amphibians.
By far the most worthwhile bare soil area to search is the leaf-cutter ant nest, which is not only teeming with various prey items but also provides habitat for a variety of animals whom the ants allow to live in their space. The ants are busy collecting and storing leaves. Inside the nest the ants use the leaves to grow a fungus, which the ants eat. The decomposition process of producing the fungi becomes a heat source in of itself, even during the coldest nights in the forest. Heat-seeking animals are not only aware of this; some reptiles will even lay their eggs in or near leaf-cutter nests to incubate them. This works alongside the obvious abundance of underground space in which snakes and frogs can live, provided the ants don’t kick them out!
The final place to mention is the prize that comes with working in tropical rainforest environments. The presence of very large trees in concordance with often thin and weak draining soils means many plants do their best to stay standing by widening out their base of support. In many tree species this takes the form of buttress roots. Named for the architectural structure that supports church arches and the like, buttress roots generally take a triangular form running from the main trunk of a tree out to areas of ground surrounding it. More often than not, the buttress roots become a tangled mess with numerous folds and fissures, the structure of which presents many obstacles and opportunities to the animal community. The many enclosed spaces created by the tree buttress may serve as perfect living spaces for herps, and long- horizontal-running roots can become natural walls, which can collect dispersing animals. The positive attributes for finding animals inside the buttress are obvious, but the total effect is observable from a slightly different perspective. The quintessential place to find a snake would be curled up against the side of a tree buttress, but the times that that actually occurs can be counted on one hand. While multiple reptiles may be living inside the buttress, they will generally stay deep within the structure where they are completely out of sight. The time when we can encounter them is when they are out and active in the forest. Inside and against the buttress is nowhere near as valuable as within the range of the buttress’ intensifying effect. Herpetologists have found that the number of observations of animals goes up when you’re within ten meters of a buttress. So to increase your chances of finding something it will still be a good idea to walk around the tree buttress, but looking outside the buttress at the multiple stems and leaf litter areas that lie close to it will be more productive than going straight in.
And above all, be patient and keep looking and listening, and something magical and herp-like will certainly appear and take shape before your eyes. Happy herping!