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Weak social ties a killer for male whales

Posted on 25 October 2017

Male killer whales are more likely to die if they are not at the centre of their social group, new research suggests.

Scientists from the universities of York and Exeter and the Center for Whale Research (USA) found the most socially isolated males were three times more likely to die in any given year than those in the ‘most central social positions’.

The effect was much stronger in years where food was scarce, and it did not affect females – possibly because males are larger and need more support from the group to get enough food.

The findings come from research on Southern Resident killer whales, a critically endangered population in the Pacific Ocean that – following a recent death – numbers just 76.

Co-author on the study Dr Dan Franks, from the University of York’s Department of Biology, said: “In our study, whales in a central social position spent time either socialising with many different individuals within their group, or socialising between two or more different social groups.

“These social males survived better than other males, showing that – like humans – other animals benefit from a strong social network and suffer when they lack social support.”

The research, funded by the Natural Environment Research Council, is published in the journal Proceedings of the Royal Society B.

Lead author Dr Samuel Ellis, of the University of Exeter, said: “This research highlights the importance of social bonds to male killer whales, and shows that males that are less socially connected are more likely to die when times are hard.

“Killer whales are highly cooperative, and males at the centre of a social group are likely to have better access to social information and food-sharing opportunities.”

Southern Residents were among the groups from which killer whales were taken into captivity in the 1960s and 70s, and human activity is now posing much greater threats to their survival, according to Ken Balcomb from the Center for Whale Research.

He said: “Salmon is the main food for these whales, and stocks have been driven down by overfishing and the blocking of spawning grounds by damming rivers.

“These factors make it all the more important to understand the drivers of survival and mortality among these whales.”

Social relationships

Previous research has shown sociability has an effect on human life expectancy, but this is the first study to show that social position across the lifespan can predict survival in non-human animals.

“These whales have been studied for more than 40 years and they are all recognisable by unique markings,” said senior author Professor Darren Croft, of the University of Exeter. “By seeing which whales regularly swam together across a year and across multiple years, we started to understand a network of what in humans we would call friendships.”

Professor Croft added: “On a broad scale, research like this examines the fundamental question of why social relationships and friendships have evolved.”

For more information on the Southern Resident killer whales please visit the Center for Whale Research website.

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