Cashew Frog (Nyctimantis rugiceps), Amazon River, Loreto, Peru
This is a wide angle, natural light shot taken in the rainforests along the Amazon River (Loreto, Peru) using a Sony a77 and a Sigma 10-20mm lens – September 2018. Background info: Of the thousands of thunder storms that soak the rainforests of the upper Amazon Basin, some storms do a little more. Sometime in the past, thunder roared as a lightening bolt hit an emergent tree along the Amazon River in Loreto, Peru. The lightening split the top of the tree trunk but didn’t kill the tree. With time and lots more rainstorms, the lightening damage turned into a cavity in the tree that now holds gallons of water. This private pool in the treetops was too much to pass on for a certain species of amphibian called the “Cashew Frog.” The frog gets its name from the smell of the defensive secretion it produces when handled – a dead ringer for cashew fruit. This species of frog (Nyctimantis rugiceps) is a little different from most amphibians in these forests in that it never needs to come down to the forest floor. Fast forward a few years after the storm that caused the tree damage and I’m hiking along the forest floor beneath the same tree. I hear a double “knock” ring down for the treetops. I immediately knew what the vocalization came from. I’ve heard the call before and have spent the time chasing it down… which required a climb up a trunk to a tree hole. The calling card was a welcome one… like an old friend calling you on the phone when you haven’t heard from them for years. The last time I had seen this species was well over 20 years ago during field work in Ecuador and Peru. In this case, with some time and careful listening, we were able to identify the spot where the frog lived. A bit of a climb and a dip of the arm into a water filled tree hole, all the way to the bottom of the cavity, and there was our frog. In fact, there is an entire assemblage of amphibians that have tricks allowing them to reside in the heights of these steamy forests. The big draw for many amphibians to visit the forest floor comes with the breeding season. Most amphibians have aquatic larvae and forest pools or streams serve as spawning grounds. The first and largest component of our “canopy frog” assemblage falls into this category – they live in the forest canopy but need to return to the forest floor to breed. The second group is different from the first in that these animals don’t need to visit the forest floor – this group includes our Cashew Frog. These amphibians live and breed in water filled tree holes or other plant-held waters. The lofty water sources are key resources and are known scientifically as “phytotelmata” – plant held waters. But there is a problem with life in phytotelmata… there isn’t a lot of food in them for hungry, developing tadpoles. Most species that have evolved into this niche care for their tadpoles in some way. For example, distantly related frogs, the “Amazonian Milk Frogs” (Trachycephalus cunauaru and T. resinifictrix) deposit their eggs into the same water filled tree holes throughout the breeding season. Tadpoles that have hatched out are quick to eat the newly deposited eggs and use them as a key nutritional resources as they develop. Other canopy inhabitants like Central America’s Thorney Crowned Treefrog (Anotheca spinosa) feed infertile food eggs to their tadpoles as they develop (a behavior known as oophagy)… known from a host of other frogs, including a few species of poison frogs (family Dendrobatidae). The last category of frog that can inhabit the forest canopy and not worry about visiting the forest floor are the direct developing species. These frogs (and salamanders) deposit eggs where all developmental stages unfold within the eggs – they don’t have a free-living larval stage. Miniatures of the adults hatch out from the eggs. So there you have it, a little canopy biology and the tricks that some amphibians use to live there.