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