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.