Amazon river dolphins look very different from marine dolphins. Born grey, adult Amazon river dolphins turn pink or pinkish-grey as they mature20. Mature males are pinker than females, which could be due to frequent aggressive interactions with other males. As wounds heal, they are covered with pink scar tissue that eventually replaces their grey skin21.
Amazon river dolphin. Illustration by Uko Gorter.
Unlike other dolphins, the Amazon river dolphin has a flexible neck which allows it to move its head 180 degrees21, 22. This makes it possible to manoeuvre through underwater branches and roots in search of their prey. Almost blind and with a highly pronounced melon (the term for the dolphin’s forehead where echolocation clicks are amplified), the Amazon river dolphin uses its bisonar to displace and localize its prey in the turbid and muddy water23.
Amazon river dolphins have characteristically low, ridge-like dorsal fins on their backs shaped like a keel; long, slender snouts; plump bodies; ‘chubby’ cheeks with sensory whiskers; and round, bulbous foreheads. They can reach 2.8 m in length and 180 kg, making them the largest of the six river dolphin species. Their pectoral fins are large and have a wide angle of rotation. Like other dolphin species, Amazon river dolphins rely heavily on echolocation to navigate and find food in the dark and sometimes turbid waters where they live. However, their eyesight is thought to be more developed than other river dolphin species.
Reproduction and growth
Females reach sexual maturity between 6 and 10 years of age and a body length of 175-190 cm 20, 23, 24. Males reach sexual maturity at about nine years old. Females give birth for the first time at an average age of 9.7 years. Gestation lasts about 11 months, and females give birth to a single calf, which is roughly 75 cm long and weighs 7 kg25. Births can occur throughout the year, but peak during high water levels when the flooded forest provides a quiet and safe place between inundated roots and branches3. The average interval between births is 4.6 years26. Males have been observed apparently trying to ‘woo’ females with clever ‘tricks’ such as picking up floating plants or pieces of wood with their beaks, twirling in circles and then smacking the object on the water’s surface. They can live for up to 40 years23, 26.
The Amazon River Dolphin, Inia geoffrensis, Tapajos River, Santarem region, Pará State, Brazilian Amazon. © WWF-Brazil / Adriano Gambarini
Amazon river dolphins are the only dolphin species that have the equivalent of molar teeth, much like humans do. All other dolphin species have only pointed conical teeth27. Molars allow them to crunch up particularly hard skinned fish. Their diet is quite broad, including over 40 species of fish, turtles, shrimp and crabs24.
The Amazon river dolphin, Inia geoffrensis, Tapajos River, Santarem region, Pará State, Brazilian Amazon. © WWF-Brazil / Adriano Gambarini
They are natural gymnasts, often pivoting, swimming backwards and upside down. Active day and night, they appear inquisitive and playful to human observers. They have been known to approach canoes, grabbing a paddle in their beaks and making off with their prize. They can also throw sticks and weeds, pull grass underwater and ‘play’ with turtles, snakes and fish. While observations of larger groups feeding together in one area have been recorded, these dolphins are usually found alone, in mother-calf pairs or in small pods of 3 or 4 individuals 3.