Two species of dolphin have struck up a friendship, helping each other defend territory, look for food and even play together, a study has revealed. Scientists have even observed one species babysitting the other’s offspring. Atlantic spotted dolphins and bottlenose dolphins were studied by The Wild Dolphin Project in The Bahamas over the space of 30 years, providing unprecedented insight into how the species rely on each other. With the exception of primates, there are few long-term studies on interspecies interactions of mammals, according to the researchers. Different species of dolphins interacting has been observed before, but accounts are largely anecdotal. But this study, published in the journal Marine Mammal Science, offers a rare glimpse into the complex relationship these dolphins have developed, built upon 30 years of observations.

‘What is unique about our study is that we can actually see them underwater, so we know what behaviors they are actually doing together,’ study co-author and Wild Dolphin Project founder Denise Herzing told MNN.

‘They travel together, socialize together, form interspecific alliances when threatened, babysit each other’s calves.’

Males from each species have been seen teaming up to chase away intruders, and female spotted dolphins have been observed babysitting bottlenose calves.

The favour is not returned by bottlenose mothers, however females from both species have been seen spending time together.

The precise reason why the two species are cooperating is not entirely clear, but the researchers say it has been observed too often for these encounters to be considered an anomaly.

The species seem to be taking part in behaviour observed in humans when forming alliances, and the study’s authors suggest this offers an evolutionary advantage.

‘These interactions likely evolved to allow the species to share space and resources and maintain a stable community,’ co-author Cindy Elliser told New Scientist.

Working together also boosts safety for the dolphins - seeing as they have shared territory, they are better off working together, according to Elliser.

The study offers further evidence that dolphins have complex social intelligence. This has been shown previously by studies that show that they use individual names for each other and even diffuse fights.