Researchers have confirmed that a wild female dolphin “adopted” a calf whose mother died in an accident, despite having no genetic or social association with the parent.
The adoption behavior was observed for the first time by a research team from Kindai University.
“The finding could shed light on how mutual aid has developed into one in human society,” said Mai Sakai, an instructor of animal behavior at the university.
The findings were published in the British journal Scientific Reports on April 6.
The team first spotted the pair in June 2012 while observing wild Indo-Pacific bottlenose dolphins in waters near Mikurajima island in the Izu island chain located about 230 kilometers south of Tokyo.
They observed an 8-year-old dolphin nursing a calf whose 15-year-old biological mother died after being caught in a fishing net. The female dolphin was found to have raised the calf for about 100 days since their first observation of the pair.
DNA testing on the foster mother revealed that she is not closely related to the biological mother such as sisters. The research team also looked into observation records and discovered that the foster mother and biological mother were “strangers” to one another.
About 120 Indo-Pacific bottlenose dolphins live in waters near Mikurajima.
The latest finding came as a result of research that has been conducted steadily since 1994 on identifying individual dolphins by taking underwater images.
Although there are other mammal adoption cases, including a dog raising an orphaned kitten, those cases usually involved a special situation, such as the animal who became a foster parent was also raising its own offspring at the time of adoption or having lost its own baby, the researchers said.