The Amazon River dolphin, or, otherwise called Boto dolphin is one of the five river dolphins and is the most famous species of the group. The body of this mammal is long and plump, whereas the fins remind paddles by their shape. In addition, the animal can be easily identified by having a ridge on its back instead of a dorsal fin. The Amazon River dolphin also stands out from other dolphin species due to its coloration, ranging from bluish grey to white, and, sometimes, pink. Some vertebrae of the dolphin are unfused, making the neck of the animal amazingly flexible, which allows the dolphin to move its head in almost all directions. The animals have been treated with suspicion by local people. Moreover, the Amazon River dolphin is a subject of numerous myths and tales. According to one of the stories, these animals become handsome men in order to seduce young women, coming to the water.
The Amazon River dolphin is a South American mammal, distributed across the drainage basins of the Orinoco and Amazon Rivers and primarily occurring in rivers and streams with slow current. As the wet season comes, the water level increases, flooding surrounding forests. During this period, the dolphins usually leave the deeper streams to swim through the trees.
The Amazon River dolphins are typically found solitarily as well as in pairs. However, there have been recorded dolphin groups, consisting of up to 15 individuals. The Botos are most active in the early morning and late evening. These animals are neither fast swimmers nor deep divers, often preferring to swim on the water surface. Spotting a boat in the water, these curious dolphins swim up in order to explore it. The Amazon River dolphins are highly communicative animals, sometimes interacting with other dolphin species. Rolling, lob tailing and flipper waving are common behavior among these playful animals. Moreover, they frequently play with their logs as well as pull at underwater grass. Also, these dolphins can often be seen playing with turtles, fish and other aquatic life forms.
Currently, very little is known about the mating system of these animals. Thus, the dolphins were thought to be monogamous, but recent studies have discovered facts, indicating other types of mating behavior in this species. Males of these dolphins are noticeably larger than females. They display extremely aggressive behavior: because of biting and abrasion, male dolphins often damage their fins, flukes, and blowholes. On the other hand, tooth-raking leads to scarring. The reason of this behavior can be tough competition for mating rights, which brings us to polygynous mating system. In the meantime, they are likely to practice polyandry and polygynandry - a mating system, where both males and females have a number of mates. The breeding period occurs in October - November, while the gestation period lasts approximately 11 months. The female dolphin normally yields a single baby with an interval of up to 5 years. As soon as the baby is born, the mother immediately helps the youngster to come to the water surface for air. The calf is nursed by its mother for about a year after birth, becoming independent within 2 - 3 years. Male dolphins are ready to mate at 7-12 years old, whereas females - earlier - at 6-10 years old.
: Presently, one of the major threats to these animals' population is continued development of the river systems, which are the natural habitat of these dolphins: they suffer from separation of their range into smaller section due to hydroelectric or irrigation schemes, damming rivers. Feeding upon aquatic animals, the dolphins compete with local fishermen. Moreover, the animals are threatened by the fishing process, during which they can accidently be caught in fishing nets or injured because of collisions with boats and motors.
According to the IUCN Red List, the total population size of the Boto is unknown for today, but there are estimated populations in certain areas. Thus, in the Amazon basin there are: 107 individuals in the Solimões River (Brazil), 346 the in the Amazon River bordering Peru and Colombia, around 260 individuals in the Mamirauá Lake system of Brazil and 13.000 individuals in the Mamirauá Sustainable Development Reserve. The Orinoco basin holds: 122 individuals in the Apuré River (Venezuela), 14-15 individuals in the Orinoco River (Venezuela) and 8 individuals in the Casiquiare River (Venezuela). Currently, Botos are classified as Data Deficient (DD) on the IUCN Red List.
Amazon River dolphins have an important role as predators of the river, and prey on a range of fish species, thus controlling their populations.