Seasonal changes have a significant impact in every natural environment, but perhaps nowhere is that effect as dramatic as in Amazonia. Annually, Amazonia is hit by a deluge that overwhelms meadows where animals have resided for nearly half the year. For four months, the Amazon is hit by torrential rain, yet even some of the highest rainfall on Earth does not alone explain the 30 to 45 foot upsurge in the water level. The answer lies 2,000 miles to the west, in the Andes reservoir of ice. The mountains' seasonal snowmelt creates a force 12 times more powerful than the Mississsippi. Each second, seven million cubic feet cascade from its slopes.
As the snowmelt fills the Amazon and rain falls, water swallows up tens of millions of acres of rainforest. As the floods advance, they leave no habitat untouched, engulfing forest up to 12 miles from the main channels. Some are destroyed; others created anew. All are transformed. By the end of the rains, the waterlands have become a vast, slow moving lake dotted with trees and broken by the half-submerged spits of flooded archipelagos. These flooded forests harbor the greatest diversity of aquatic life.
Featured Wildlife: Waterworlds
Giant otter (Pteronura brasiliensis)
The rarest mammal in the Amazon, the giant otter is recognized internationally as a highly endangered species. Once hunted for their fur, the reclusive otters now thrive only in the remotest jungle. At over six feet long and three times the weight of other river otters (more than 70 pounds), their name is no exaggeration. Typically, giant otters live in groups of five to nine animals -- rarely are they found living alone. Each group is comprised of an adult pair and their offspring, which may be from different breeding years. Though they feed mostly on fish, giant otters have been known to eat small reptiles, including snakes and caiman. As they do nearly everything else, giant otters hunt together as well, swimming underwater in formation and surfacing to breathe.
One could well hear a giant otter before seeing it. A highly communicative species, giant otters have the gift of the gab, and constantly interact through high-pitched hums, whining squeals and screeches. When the otters become scared or concerned, they surface out of the water, craning their necks, and snort loudly.
Piranha (Serrasalmus sp.)
Thanks to the movies, piranhas have a fearsome reputation in the popular psyche. But of the some 20 species of the fish in the Amazon, most are vegetarian, which explains why piranha are able to co-exist with other fish species. If all piranha were as predatory as the most carnivorous piranha species -- the red-bellied piranha -- there would be scarcely any fish left in the Amazon. This is because the red-bellied piranha's razor sharp teeth can shred flesh from bone in a matter of seconds.
Tucuxi (Sotalia fluviatilis)
The tucuxi is one of two species of river dolphin that inhabit the Amazon. Scientists believe that the tucuxi entered the Amazon when the river finally reached the Atlantic Ocean; today, the tucuxi is the only member of its hereditary family that lives in freshwater. Carnivorous dolphins, tucuxi live in groups of up to nine, are highly intelligent, and are superb hunters. They enter the Amazon basin's lakes when the river floods, and as the floodwaters retreat, they leave to avoid being stranded. Between three and five feet long, and weighing as much as 110 pounds, tucuxi are extremely acrobatic, and often leap clear of the water. Their diet consists primarily of fish.
Like other formerly marine creatures, turtles have adapted to life in the Amazon. Giant Amazon river turtles are magnificent to behold, reaching up to three feet in length and weighing as much as 110 pounds. They are best known, however, for their elaborate egg-laying ritual, which occurs during the Amazon's low-water ebb each year. Over the course of several weeks, female turtles return to the sandy beaches where they were born to lay their eggs. Come nightfall, each female digs a hole up to three feet deep. When it's ready, she puts all of her eggs into one sandy basket -- up to 180 of them, arranging them carefully with her tail. After two hours of hard labor, the mothers will not return for another year.
Forty-five days after the giant turtles leave their sandbank, the eggs they buried start to hatch. Few of the newborn turtles survive for very long. But in her lifetime, a female turtle lays so many eggs that if only one in a thousand survives, it may be enough for the species to continue to thrive.
Piraracu (Arapaima gigas)
At eight feet long and weighing as much as two men, the air breathing piraracu is one of the world's largest freshwater fish. When they are born, piraracu have gills, but they quickly atrophy. Instead, as the piraracu matures, it breathes through a lung-like organ similar to the lungs of non-fish vertebrates. An adult piraracu will breath once every 10 to fifteen minutes. If necessary, however, they can stay underwater for twice that time. The piraracu thrives in stagnant, low oxygenated lagoons where other smaller fish -- lacking the piraracu's adaptations for air breathing -- become listless, easy prey. The piraracu has a particularly nasty adaptation for hunting as well. Its large, toothed tongue, when combined with its teeth, functions as an extra, lethal set of jaws.
Manatee (Trichechus inunguis)
Also known as the water ox, the manatee is Amazonia's largest marine mammal, weighing over a thousand pounds at over nine feet long. Voracious herbivores, the manatee eats up to 110 pounds per day -- a significant percentage of its body weight. An endangered species, the manatee's closest living relative is the elephant.
Manatees feed heavily during the wet season, during which time they build their reserves. No one quite understands how manatees are able to do this, for being able to consume this much food means navigating through the slow-moving, brackish backwaters of the Amazon. Their small brains don't hint at great intelligence, their eyes are poorly developed, their ears tiny, and they close their noses underwater to avoid drowning. Yet mysteriously, they are able to navigate. During the dry season, the manatee is able to shut down all but the essential body functions, and can fast for up to six months.
Boto dolphin (Inia geoffrensis)
Larger cousin of the tucuxi, the boto dolphin reaches lengths of nearly seven feet and weighs over 300 pounds. Unlike their more social relatives, however, the boto is a solitary creature, swimming the Amazon alone as it feeds on catfish, crabs and turtles with its sharp teeth.
There are other key differences between the boto and the tucuxi -- for example, the boto rarely will leap from the water. Most significantly, the neck vertebrae of the boto are unfused, meaning that the boto can move its head from side to side. This ability contrasts with marine dolphins, whose necks are fused. As a result, the boto is capable of exploring a wide range of its immediate environment with one sweep of its neck.
Electric eel (Electrophorus electricus)
The murkiest waters of the Amazon present no challenge for the electric eel. Five feet long, the eel is practically blind. But instead of relying on sight to explore its environment, it generates an electric field around its body to sense the presence of prey. Once prey has been located, the eel discharges five times the voltage of a household socket, stunning or sometimes killing its victim.
Interestingly, the electric eel is unrelated to other fish commonly known as eels. The electric eel is the evolutionary offshoot of an ancient, primitive air-breathing fish found throughout Central and South America. Electric eels use their gills for breathing from the air and for absorbing oxygen from the Amazon.