Apparently, some females like to be wooed with gifts. In the case of Amazonian river dolphins, weeds are much appreciated.
Marine mammals are notoriously difficult to study, due to their aquatic habits and ability to move over large distances. This three-year research project was conducted in Mamiraua, a rainforest reserve in Brazil. Along with extensive observations of individual dolphins and groups, tissue samples were taken to analyze genetic relationships.
The data suggest that adult males carry objects such as sticks, clay, or weeds to attract females. Those individual males that often display objects also tend to be successful at mating and fathering calves. This finding puts Amazonian river dolphins in a select group of animals known to use tools. In this case, the object becomes a display to attract females and thereby gain greater reproductive success.
The pink river dolphin (Inia geoffrensis), known as the boto in Brazil, is considered highly intelligent compared to other freshwater dolphins. They are described as highly curious. Dolphins often feed alone, but may cluster into small groups. Prey species include small fishes and crustaceans. This dolphin species has several distinctive features, including a long narrow beak, a reduced dorsal ridge, and the ability to turn its head (owing to unfused vertebrae). Stiff beak hairs allow foraging in murky water and bottom sediment.
This species is found in freshwater from the Amazon River delta to the Andes, including parts of Brazil, Peru, Ecuador, Colombia, Bolivia, Guyana, and Venezuela. Its range overlaps with that of the tucuxi, another freshwater – and saltwater – dolphin species. Much of the freshwater habitat is increasingly threatened by the destruction of the Amazonian rainforest, through deforestation and development. In addition, these dolphins suffer incidental mortality in fishing equipment, particularly gill nets. Hydroelectric dams and pollution from mercury mines are additional challenges.
Other river dolphins have been disappearing over recent years – the Chinese river dolphin or baiji is now considered potentially extinct, after surveys failed to spot any animals. The Ganges river dolphin, Indus river dolphin, and finless porpoise are endangered, while the Irrawaddy dolphin is critically endangered. Only the two South American river dolphins have viable populations – for now.
I had no idea that dolphins even lived in rivers. I hope something can be done before they become extinct. I have always loved dolphins.