London, Oct 25 (IANS): Male killer whales who remain socially isolated are three times more likely to die in hard times than those in the centre of their social group, researchers warn.

The findings showed that 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.

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, the researchers said.

"A central social position meant whales either having many individual connections or being the connection between two or more groups," said Darren Croft, Professor at the University of Exeter in the UK.

"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," said lead author Samuel Ellis from the University of Exeter in the UK.

For the study, the team examined Southern Resident killer whales -- a critically endangered population in the Pacific Ocean.

Human activity is now posing much greater threats to their survival, according to Ken Balcomb from the Center for Whale Research -- a Washington-based non-profit.

"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," Balcomb said.

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.

"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," the researchers stated.