Why are river islands unique, and important? Notes on the role of river islands in the Amazon basin as stepping stones of evolution.
Updated April 28, 2015
Before morning, we dock the canoe and walk half an hour on boardwalks to the lodge's docks, where a boat captain awaits us. Several long days, the heat, and all that trudging through rainy forests has made me deliriously tired.
But once the motorized canoe disembarks, and we are screaming down the Napo River, my weariness fades, and I am struck with an energy whose origin I cannot immediately explain.
The Napo River is Ecuador's biggest contribution to the Amazon. It winds, twists and flows from the valleys of the Andes through the lowlands of the Ecuadorian Oriente. Throughout its length, the Napo River is, perhaps more than any other large Amazonian River, riddled with islands and sandbanks, giving the river a geographic character like a complex archipelago.
We are motoring towards the immense Yasuni National Park, stopping along the way at several islands.
We pull up to an island with a wide, sandy beach, which is lined first by layers of grasses and shrubs, and then towards its interior, inhabited by cecropia trees and fast-growing palms.
You can’t escape the sheer amount of birds on this island –martins and nightjars among the grasses of the wide sandy plains for example, and hummingbirds and spinetails in the denser shrubs at the center of the island.
Although the Amazon has the largest avian diversity in the world, the birds aren't exactly abundant. In fact, the Amazon has nothing on my backyard on an early spring morning. Why then, is this tiny river island teeming with bird life?
I walk with Carlos and Pablo through the grasses of the island, and I realize the source of my unexpected energy. The weather out here on the river itself is a perfect seventy-eight degrees. There is a light breeze, no clouds in the sky. This is the weather of the Open Amazon basin rivers, all year round. So delightful, and this is our plan for the whole day, just me, the captain, and my two guides, just visiting islands and floating through the breeze.
Some travelers believe the Amazon holds the most perfect weather in the world. For me, there is something about open blue sky without shade that captures me, sucks me in.
In the grasses I am surprised to find three boys, aged about three years apart. They are playing joyfully, digging in the sand, following us, hiding in the reeds. They are here alone without supervision. Their canoe is parked on a sandbank on the other side of the island. But where is their village? There is only jungle on either side of the river.
For many in my generation and before, the clearest memories of boyhood were like this one; long hours of independence and friendship, with the landscape acting like a big white canvas, waiting to be painted.
I wander off by myself, and am surprised to again meet some people, strange since there is little evidence of humanity for miles along this river. A birding guide and his clients from Spain. By a bizarre coincidence, I had met this guide on the airplane from Quito. He had just returned from his first time traveling Ecuador as an independent guide. We talk for a few minutes before Pablo emerged from the woods, stunned and surprised, both that his younger brother is here on this tiny island, and how on Earth do I know him?
Pablo and his brother spent their childhoods much like the three children hiding in the grasses, with the Napo River and all its complex geography as their blank canvas. As adults, both earn their living by doing what they loved as children.
When we renew our focus on the island itself, I can see that the island is little more than a sandbank, which by the shifting nature of the Napo River, was able to make its hold against the river through the flood season.
Often, the islands form as deposits of sand build-up along the curves of the river. Sometimes, the islands are the results of the river itself subtly changing course, cutting slices out of riverside bends.
River islands on the Napo are temporary. A strong storm, a rainy season, the shifting course of the river itself can all tear any of these islands apart in an instant. Why have so many birds evolved to take advantage of such a peculiar, dangerous habitat?
Back home in Oregon, I can walk a quarter mile from home and run into dozens of habitats, each of which I might recognize as being suitable for a certain kind of bird. Even the way the light falls on a place, the size of the branches, the amount of moss, the presence of steep cliffs, the species of tree, the presence of dense shrubs nearby, and so on and so forth, can tell me an abundance of information about what that might be fluttering in the distance.
But the Amazon, to us North Americans, seems unendingly the same. Intense and awe-inspiring, yes, but not with the variation that comes with our North American habitats.
Some birds in Oregon, such as the diminutive wrentit, cannot be found in the state of Washington, simply because the mouth of the Columbia is too long a flight. In the Amazon, rivers are a natural part of the explanation for the vast avian diversity here. River edges are often nearly impenetrable borders for species, which are often incapable of flying very far at all. As rivers change course and form new paths through jungle, populations get split into two, creating the perfect opportunity for a species to split as well.
It is not true that all of the Amazon is the same. There are indeed very distinct habitats, simply unrecognizable to us. So, while rivers are important to the story of birds in the Amazon, river islands, which are fiercely different from any other type of habitat in the Amazon, play a distinct habitat role.
We leave this island and hop to another. This island has survived for over two decades, and so while the former island was composed mostly of reeds and grasses, this one has established a forest of fig trees and cepropias; pioneer species that have themselves cut their own evolutionary niche. These trees specialize in taking root before anything else does. They live fast, grow fast, die fast. Their strategy is not to find permanent settlement, but to keep their species planted in the niche that they are best suited for.
Curiously, the dozens of bird species that specialize in river islands prefer the younger islands, composed mostly of reeds and islands. Older islands, with larger and more established trees, begin to collect birds that you might find along the river edge. But why are the populations densest and most diverse in the simplest habitats? Those reeds and grasses, adjacent the lush river water, attract a bounty of insects, but no predators. A species which can evolve to inhabit the fast-paced and dangerous lifestyle of an island always at the edge of being swept away has a special advantage – a bounty of food like nowhere else in the Amazon, without the trouble of snakes, lizards and mammals.
It is believed that because river island pioneers are adapted to moving along the rivers from island to island, and so their habitat stretches out over thousands of miles of Amazonian waterways, these birds may have helped buffer the Amazon against the climatic events of the past, which could crush isolated pockets of other species. But if you have dozens of species that can survive along a range of thousands of miles, you have the ability to reseed populations after severe climate events. So while these tiny river islands may be the least likely place to look for life, they may, in part, help explain why there is so much of it here.
We continue downriver, into the water that borders the Yasuni National Park, believed by some scientists to be the most biodiverse place on Earth. Along the way, we see only a handful of small fishing canoes. More regularly, we see oil boats.
Texaco is everywhere along this river, which holds vast petroleum reserves. Fires rise from the jungle and barges ply the open water, from extraction site to extraction site. But the history of conflict between oil and indigenous populations in the Ecuadorian Amazon, the pressure of international environmental groups, and the watchful eye of a native President keen on how oil interests exploit indigenous populations, has advanced a peculiar strategy to keep the rich Yasuni free of oil extraction. The Yasuni-ITT Initiative is a plan to permanently ban oil extraction from the Yasuni National Park, which holds about 20 percent of the nation’s reserves, in exchange for payments of about roughly half the value of the oil from national and international interests. Still in fundraising stage, the initiative has been gaining traction and attention worldwide.
When we again depart the boat, we walk into the vast wilderness of the Yasuni. Moist, humid, dark, filled with life. After climbing a ridge, we find a fresh cougar print on the trail. Vines filled with flowers dangle from trees whose tops we cannot see. Up there, we can hear macaws chattering. We hear noise everywhere, and the only thing we cannot hear is the sound of oil boats plying the water along this vast island of diversity.