In a crisis you realise who your friends are 鈥� even if they don鈥檛 belong to your species.
The bottlenose and spotted dolphins of the Bahamas are unusual in that they often intermingle.
Now, observations show these unusual coalitions survived two deadly hurricanes. Afterwards the dolphin interactions were less aggressive, perhaps to allow them to adjust to post-disaster life.
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Bottlenose and spotted dolphins in the Bahamas play and forage together, sometimes even babysitting each other鈥檚 young. But bottlenose males also routinely use their size advantage to forcibly hone their mating skills on their smaller cousin species.
In 2004, two hurricanes swept through the Bahamas. Both dolphin species lost between 30 and 40 individuals 鈥� about 30 per cent of their respective populations.
鈥淭hey interacted with those dolphins every day for years,鈥� says Cindy Elliser at in Anacortes, Washington. 鈥淟osing them really threw a wrench in everything.鈥�
Social networks
Adding to the turmoil, about 30 new bottlenose dolphins then migrated into the area, leading to a major restructuring of social networks.
But even as this restructuring continued, Elliser and her colleague 鈥� Denise Herzing at the in Jupiter, Florida 鈥� found that bottlenose and spotted dolphins continued to intermingle.
We don鈥檛 know exactly why, says Elliser. But she thinks the mixed species encounters may have taken on added significance as a way to solidify any remaining, pre-hurricane relationships 鈥� as well as helping to build new ones.
This may have been especially important to the bottlenose dolphins, because their within-species social networks had to adapt to the loss of familiar faces and the appearance of unfamiliar newcomers.
That might also be a factor in why male bottlenose dolphins no longer forced themselves on spotted dolphins during cross-species interactions.
鈥淭hat was the most surprising thing,鈥� says Elliser. The aggressive behaviour is very dramatic and easy for us to recognise, she says, which can make it seem like a very important part of the cross-species interactions.
Peaceful foundations
But it seems that actually it鈥檚 the subtle, peaceful behaviours that form an important foundation for the interactions, says Elliser.
Maddalena Bearzi of the in Marina del Rey, California, studies cross-species interactions involving bottlenose, common and Risso鈥檚 dolphins off California鈥檚 coast.
鈥淚t鈥檚 important data,鈥� she says of the findings from the Bahamas. 鈥淚t makes you want to gather more info about how social structure changes after an event like a hurricane 鈥� or El Ni帽o.鈥�
Elliser says the dolphins did eventually begin to display more of the social behaviours seen before the hurricanes 鈥� including the aggression 鈥� but not until five years after they hit. 鈥淭hat shows how long it takes a community to get back into those 鈥榥ormal鈥� behaviours,鈥� she says.
Bearzi agrees. 鈥淭hey can recover but it takes a long time,鈥� she says. 鈥淚n future, with climate change, we will probably have more and more of these issues.鈥�
Journal reference: Marine Mammal Science,
Read more: 鈥�Nature鈥檚 strangest families: Why animals adopt鈥�; 鈥�Dangerous liaisons: Fatal animal attractions鈥�
