The darker side of dolphins – they 'resort to rape' scientists say
DOLPHINS can resort to ‘rape’ to assert authority and live complex social lives in an ‘open society’ where regular homosexual and bisexual relationships are formed, according to scientists.
The conclusions from the international team of scientists came after they spent the past six years studying the behaviour of 120 bluenose dolphins in Shark Bay, Western Australia.
In one of the most extensive studies of its kind, male bottlenose dolphins were also found to organise gang-like alliances, in which they guard females against other groups.
In some instances, males would assert their authority by forcefully mounting other males and other such violent sexual behaviour.
This was viewed as a short-term show of strength in order to dominate males from other groups. As they recorded their movements, others were observed to steal fertile females away.
While most animals formed alliances to defend their territory, the study did not find any evidence of this.
During their observations, they did find animals roamed hundreds of square miles in which they often encountered other dolphin groups.
Reporting in the journal Proceedings of the Royal Society B, they concluded the highly intelligent mammals lived in an "open society".
Prof Richard Connor, the study's co-author, said dolphins would have to be incredibly intelligent to understand the "soap operatics" of their lives.
"I work on the male dolphins and their social lives are very intense," he told Discovery News.
“It seems there is constant drama. I have often thought, as I watched their complicated alliance relationships, that their social lives would be mentally and physically exhausting.
"It seems there is constant drama. I’m glad I’m not a dolphin.”
Prof Connor, a biology professor from the University of Massachusetts, Dartmouth, added that rather than males guarding a specific territory, groups have a "mosaic of overlapping ranges".
Prof Connor, who first began his studies of the Shark Bay dolphins in the early 1980s, said that while males were "capable of serious aggression," they did not constantly row and did not patrol and defend particular areas.
In their latest study, researchers found that the dolphins lived in an "open society" where allies were swapped with remarkable frequency.
Alliances were found to be switched as dolphins battled against larger, tougher challengers.
The dolphins were all tagged and given names, such as "Captain Hook" and "Flat Fin" that were based on the shape of their fins.
The team found dolphins also organised themselves into three different kinds of groups that could overlap. One group, usually in pairs or threes, was tasked with gathering fertile females during mating season.
In a "second-order alliance", the animals form "teams" of between four and 14 males which mount attacks on other groups to take their females, or to defend against attacks.
The third group maintained “friendly relations” with all dolphin groups and helped out various teams when additional forces were needed.
The team found the males made a series of alliances with the same sex. They only observed one group of females forming a temporary coalition against young males.
Only humans and the Shark Bay bottlenose are known to have these multiple levels of male alliances in their social network.
Dr Nichola Quick, a researcher at the University of St Andrews' Sea Mammal Research Unit, said that understanding how animals managed social interactions in the wild was crucial in order to "truly understand their behaviour".
She told BBC Nature: "If, for example, we are interested in impacts of [human] activity on animal, we can only really tell if an impact has occurred if we know what the animals 'normally' do."
Scotland's has a resident population of bottlenose dolphins based around the Moray Firth. There are about 130 bottlenose dolphins in the inner firth and are one of only two known resident populations of the species in Britain.
The study is just the latest example of dolphin intelligence.
The creatures have been found to communicate through body language and can also be taught to understand basic elements of human language such as vocabulary, questions and demands.