Dolphins who need dolphins

Researchers at the Dolphin Communication Project get a lot of questions from the public about dolphin behavior, but one question above all the others has given us the biggest kick. And, sparked a rather interesting answer. The question, posed to us once by a young dolphin enthusiast, was ‘How do dolphins get married?’ Not ‘do dolphins get married’ mind you, but ‘how do they get married’. To date, I am aware of only one bona fide wedding ceremony that involved a dolphin (check out website for details), but as a general rule, dolphins don’t marry other dolphins, at least in the way that humans marry other humans (as far as we know).

Dolphins do socialize with other dolphins in very complex ways, and some dolphins do appear to form life-long friendships. But, describing the social networks of dolphins is also a very complicated science. There are as many multifaceted dolphin social systems as there are dolphin species. Orcas, for example, are famous for living in matrilineal groups. In these small groups, young orcas will stay with their mothers’ family throughout their lifetime; grandmother, aunt, daughter, grandson – bonded for life. These small matrilineal groups will join with other small groups to form subpods; multiple subpods will band together to form larger pods. Individual animals will rarely leave their family pod. But this is not the case for other dolphin species, like Indo-Pacific bottlenose dolphins. For this species that the Dolphin Communication Project studies in Japan, we regularly observe a shifting group of about 160 individual dolphins that spend their days close to the small island of Mikura. These dolphins are described as living in a ‘fission-fusion‘ society: this means that individuals and small groups tend to form, disband and then reform on a regular basis, constantly changing partners. Sometimes we can spot trends in associations; the most common relationship is that between mothers and their calves – young calves spend almost all of their time by their mother’s side. But, we also see associations between two or more adult mothers, who will stick together in seemingly protective groups in order to provide their calves safety. Also, adult and sub-adult males tend to hang out together in small or large groups, as do groups of juveniles.

When scientists measure the intricate patterns of associations that describe these complex and ever-changing groups, they perform statistical tests to determine whether there are strong association patterns between certain individuals. Using these tests, scientists have found some other rather remarkable relationships between individuals that are about as close to a dolphin “marriage” as you are going to get. For the Indo-Pacific bottlenose dolphins studied by Richard Connor and his colleagues in Shark Bay Australia, scientists have discovered that male dolphins tend to form long-term alliances with one or more other males. These alliances may last a lifetime. Alliance partners are seen swimming together, hunting together, and most importantly, wooing females together. When two or more males attempt to mate with a female by isolating her from other dolphins, this is called ‘herding’. Sometimes, two or more male alliances will combine together to herd females that are being watched over by other male alliances. Combinations of more than one alliance form what are have been termed “super alliances”. For the Shark Bay dolphins, these alliances appear to be a strategy for mating and reproduction.

Still, not all long-term relationships seen with the bottlenose dolphins are between two males. Anne Weaver is an ethologist studying bottlenose dolphins along the Inter-coastal Waterway of Florida’s Gulf Coast. She has observed a long-term alliance between a male (nicknamed “N”) and female dolphin (nicknamed “DD1”). These two dolphins have been spotted socializing together on many occasions, involved in what appears to be a long-term relationship. Could this be evidence of a dolphin “marriage”? Probably not. It is unlikely that this pair has exchanged rings, picked out china, or spent any time in Vegas. But their relationship is definitely extraordinary; there are not many examples of long-term male/female partnerships in any dolphin species. Since male dolphins do not spend time caring for young dolphins, there is no real reason for them to spend their entire lives with one female. Other animal species that do form these long-term male/female partnerships (like prairie voles or many bird species) are usually both responsible for raising the kids. In comparison, male bottlenose dolphins are sometimes known to commit infanticide; they will kill young calves as an attempt to induce their mothers into a reproductive state – another strategy to get a chance at mating. So, there are always exceptions to the any of the rules of behavioral studies.

It is difficult to say what conditions must be in place for these different kinds of relationships to blossom. For example, Leszek Karczmarski and his colleagues studying spinner dolphins living close to the mainland islands of Hawaii have described these dolphin groups as having the classic fission-fusion society; individual and small subgroups tend to change relationships frequently. But they have also found that, around Midway Atoll, just a few hundred miles from the main Hawaiian Islands, the same species of spinner dolphins appear to form uniquely stable relationships. Apparently, both males and females form long-term bonds and stay in what appear to be permanent groups. This population more closely resembles the matrilineal orca groups than their cousins who live just a few miles away. Perhaps this is a result of unique environmental and ecological conditions. Or, maybe there is an underwater dolphin wedding chapel near Midway. Just kidding!

So, in answer to the question ‘how do dolphins get married’, I can only say… uh…. next question, please…

Read Ann Weaver’s story about dolphin social relationships: Ann Weaver’s research

Read the Dolphin Pod’s interview with Ann Weaver: Interview with Ann Weaver
Learn more about Leszek Karczmarski’s research with spinner dolphins in Hawaii: Leszek Karczmarski’s research
Oh boy – the only case of a dolphin marriage currently on the books…..: Woman marries dolphin
Learn more about the dolphins of Shark Bay: Shark Bay dolphins