The Amazon river dolphin, Inia geoffrensis, commonly known as the Boto or pink dolphin, is a freshwater cetacean endemic to the Amazon and Orinoco river basins of South America. It inhabits a vast network of rivers, lakes, and seasonally flooded forests. Unlike oceanic dolphins, Botos possess unfused cervical vertebrae, granting them exceptional head flexibility. This flexibility, along with their distinctive pink coloration, supports their predatory lifestyle in a complex environment.
Primary Prey Items
The pink dolphin is a generalist predator. Stomach content analysis shows the Boto feeds on over 50 different species of fish, establishing them as an apex predator in their river systems. Prey size ranges from small fish around five centimeters up to 80 centimeters in length. Their diet frequently includes armored catfish, croakers, cichlids, and various characins, such as tetras and piranhas. The Boto’s robust dentition allows it to consume prey other dolphins cannot easily handle, including small river turtles and freshwater crabs.
Specialized Hunting Tactics
Pink dolphins rely on echolocation to navigate and hunt in the murky waters of the Amazon and Orinoco rivers. They emit high-frequency clicks and interpret the returning echoes, locating hidden prey. This bio sonar system is essential because the high sediment load often renders eyesight useless for hunting.
The Boto’s specialized anatomy supports hunting success in confined spaces. Its unfused neck vertebrae allow the head to turn almost 90 degrees to either side, a flexibility marine dolphins lack. This enables the Boto to maneuver around submerged trees and dense vegetation. Their unique heterodont dentition features two types of teeth: sharp, conical teeth in the front for grasping prey, and molar-like teeth toward the back of the jaw. These powerful molars crush the tough exoskeletons of crabs and the hard shells of turtles and armored fish.
Botos typically hunt alone or in very small, loose pairs, differing from the large, coordinated pods of oceanic dolphins. They sometimes aggregate into larger groups, occasionally up to 35 individuals, particularly at river confluences where currents concentrate fish. This temporary group hunting allows them to efficiently exploit areas of high prey density, demonstrating a flexible social structure based on food availability.
Habitat and Seasonal Dietary Shifts
The annual flood pulse of the Amazon and Orinoco rivers dictates the pink dolphin’s movements and dietary patterns. During the high-water season, the river floods the adjacent forest areas known as the várzea. Dolphins venture into these flooded forests, navigating between tree trunks to exploit temporary habitats rich with dispersed fish, leading to greater dietary diversity. As the water level drops during the dry season, the dolphins retreat to the main river channels and large lakes. Although prey density is higher in these restricted areas, the variety of species consumed tends to be more limited.