Amazon River Dolphin (Boto) Facts - National Geographic

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Common Name: Amazon river dolphinsScientific Name: Inia geoffrensisDiet: CarnivoreSize: Up to 8 feet longWeight: Up to 450 pounds
Current Population Trend: Unknown

Every spring when the rains fall in South America, the Amazon River and its tributaries begin to spill their banks. Eventually, thousands of square miles of rainforest are flooded, creating a vast, tree-canopied sea.

Into this seasonal sea, which remains for half the year, swims the Amazon river dolphin, or boto. Botos have the characteristic dolphin smile and, unlike their marine cousins, bulbous foreheads and long, skinny beaks. Most strikingly, males can be pink.

The coloring is believed to be scar tissue from rough games or fighting over conquests. The brighter the pink, the more attractive the males are to females—at least during mating season, which takes place when the water has receded and males and females are confined to the river channel again.

During the wet season, however, females venture far into the flooded forest, likely to escape the aggressive males. A unique adaptation lets botos swim easily between trees and through tangles of branches: unfused neck vertebrae, which allows them to bend at up to a 90-degree angle.

In addition, the boto’s long snout comes in handy for rooting through river mud for crustaceans or darting among branches after small fish. Echolocation allows them to navigate and find prey in the dark, muddy water.

Botos are the largest of the four river dolphin species, reaching up to eight feet long and 450 pounds. They have powerful flippers and tail flukes and a modified hump in place of a dorsal fin.

Male botos sometimes beat the water with branches or grasses held in their mouth, or even hold live turtles aloft, in courtship displays aimed at impressing females. Females give birth to one calf after a pregnancy of 11 to 15 months. The young nurse for more than a year, staying close to their mothers.

Humans are the only threat to Amazon river dolphins, hunting them for catfish bait or trapping them accidentally in gill nets. Traditional Amazonian belief holds that the boto is a magical being able to take the form of a human and come ashore—with a hat to hide its telltale blowhole.

an Amazon River Dolphin

An Amazon river dolphin, also called a boto, pauses for an underwater portrait in Brazil.

Photograph by Flip Nicklin, Minden Pictures, Nat Geo Image Collection
Please be respectful of copyright. Unauthorized use is prohibited.<p>Amazon dolphins (<i>Inia geoffrensis</i>) bear little resemblance to our beloved Flipper. How did they get to the Amazon—and why are the males sometimes pink?</p> Please be respectful of copyright. Unauthorized use is prohibited.<p>River dolphins navigating the Amazon Basin's tea-colored brew of silt and rotting vegetation seem to glow orange. Out of the water they're pale gray, with some marked in pink. Called botos in Brazil, they use high-frequency sonar clicks to build a 3-D echogram of their dark world.</p> Please be respectful of copyright. Unauthorized use is prohibited.<p>At a protected inlet where tourists can marvel at their playfulness, two dolphins fight for fish. Though humans are their only predators, rough games, fierce sexual competition, and possibly even maternal discipline leave many Amazon dolphins scarred. Pink skin raked with teeth marks and tattered flukes and fins are badges of male aggression.</p> Please be respectful of copyright. Unauthorized use is prohibited.<p>From March to July, the wet-season deluge expands the dolphins' range across inundated plains and into rain forest in the Anavilhanas Archipelago, a vast island chain in the Rio Negro.</p> Please be respectful of copyright. Unauthorized use is prohibited.<p>Botos forage among flooded trees for fish, crabs, and turtles.</p> Please be respectful of copyright. Unauthorized use is prohibited.<p>Fishermen like this one on Brazil's Rio Ariaú use weighted cast nets. Such small-scale, traditional fishing methods are far less hazardous to botos than the growing use of gill nets, which can entrap and quickly kill dolphins.</p> Please be respectful of copyright. Unauthorized use is prohibited.<p>A boto's jaw muscles can snap its elongated beak down on prey with crocodilian ferocity. "It's like an industrial guillotine," says University of Kent biologist Tony Martin.</p> Please be respectful of copyright. Unauthorized use is prohibited.<p>In an exuberant display of muscle and flexibility, a boto bursts from the floodwaters.</p> Please be respectful of copyright. Unauthorized use is prohibited.<p>A male boto makes a pitch for sexual selection by tossing the outsized seed of a rain forest tree. Mating displays include beating the water with branches and river grasses, and "trophy lifting" of live turtles. "It's all to attract the ladies," says University of Kent biologist Tony Martin. "A male will surface repeatedly with an object in his beak and slowly rotate on his own axis." Much of boto life remains largely unfathomable. "We can only guess at the high-frequency singing or trumpeting that probably accompanies these very ritualistic displays," Martin says. "We're still peeping through an aquatic keyhole."</p> Please be respectful of copyright. Unauthorized use is prohibited.<p>Mother and calf stay close amid drowned saplings. Youngsters nurse for more than a year. Females have just one calf at a time, with two to three years between births.</p> Please be respectful of copyright. Unauthorized use is prohibited.<p>Imagined lords of a golden underwater city—the Encante—botos may have been shielded from exploitation by their mythical status.</p> Please be respectful of copyright. Unauthorized use is prohibited.<p>Today, as rainforests are felled and commercial fisheries move into their hunting range, people are shaping a daunting new world for these river masters.</p> Please be respectful of copyright. Unauthorized use is prohibited.<p>This wide-angle shot gives an elongated impression of the stocky boto, hinting at its kinship with whales. Descended from oceanic ancestors, these freshwater dolphins retained powerful cetacean flukes, but streamlined the dorsal fin to a slight ridge. Their adapted body form is well suited to maneuvering in a flooded inland maze of thickets and trees.</p> Please be respectful of copyright. Unauthorized use is prohibited.1 / 131 / 13<p>Amazon dolphins (<i>Inia geoffrensis</i>) bear little resemblance to our beloved Flipper. How did they get to the Amazon—and why are the males sometimes pink?</p>

Tracking Dolphins

Amazon dolphins (Inia geoffrensis) bear little resemblance to our beloved Flipper. How did they get to the Amazon—and why are the males sometimes pink?

Photograph by Kevin Schafer

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