Orcas, or killer whales, are extremely intelligent and social marine creatures. They are at the top of the food chain – no other animals (except humans) hunt killer whales. However, some populations of whales are considered “protected” according to the National Oceanic and Atmospheric Administration (NOAA).
There are a few reasons why humans might hunt these beautiful creatures, including for food, and because they are seen as competition to fisherman. These whales are well on their way to becoming an endangered species, and not just because of humans hunting them. Due to their extremely social nature, a new study shows that killer whale’s social relationships affect their mortality risk.
Researchers from the University of Exeter examined the relationship between the social position of resident killer whales by looking at 30 years of social and demographic data. Resident Killer Whales off the Pacific Northwest Coast of the USA and Canada live in hierarchal societies, so they attempted to quantify the relationship between social position of male and female resident killer whales. By studying which whales swan together over the years, the researchers were able to begin to understand their relationships. They hypothesized that this mortality risk associated with social hierarchy is related in part to resource abundance.
After carefully examining the data, the results showed that the survival of male whales, but not females, is significantly related to their social position in the community. In that males in the most central position have 1/3 of the mortality risk of those in the least central social position. However, this is only true in years of low salmon abundance.
Why are these males so dependent on their social relationships, and why are females exempt? It has been shown that resident killer whales often share the fish they catch with those that they are closer with, therefore if you have a more central positon in the community you are more likely to receive “food gifts” from others.
Dominance may also be a factor. If you hold a more dominant position in the group, you may have a more central social position and you may also have more access to resources. Competition for resources would be strong in times of low salmon abundance and therefore those who are more dominant are more likely to receive more food.
In comparison to males, females do not show this mortality risk in relation to social hierarchy, possibly just because of their size. Females are estimated to weigh up to 3338kg whereas males are estimated to weigh up to 4434kg, and therefore males require a 25% higher energetic intake, making them more vulnerable to starvation.
In the human world, it is known that relationships can affect lifespan. This is the first study that brings that idea into the rest of the animal kingdom. This important area of research shows the importance of sociality, and may help in predicting the future of endangered species. On a broader scale, this research may add to the question of why and how relationships and friendships have evolved.
Ellis, D. W. Franks, S. Nattrass, M. A. Cant, M. N. Weiss, D. Giles, K. C. Balcomb, D. P. Croft. Mortality risk and social network position in resident killer whales: sex differences and the importance of resource abundance. Proceedings of the Royal Society B: Biological Sciences, 2017; 284 (1865): 20171313 DOI: 10.1098/rspb.2017.1313