Key takeaways
- Neither sons nor daughters disperse. A pod is a mother and her descendants.
- The oldest female holds the knowledge of where food is and when.
- Females stop breeding decades before they die, and those decades are useful.
- Groups gather at good feeding and then separate again along family lines.
A family nobody ever leaves
Almost every social mammal solves the inbreeding problem the same way: at some age, one sex leaves. Young male lions are pushed out. Female chimpanzees transfer between groups. Wolves disperse and found new packs. It is close to a universal rule of mammal societies.
Orcas do not follow it. A calf born into a group stays in that group for its entire life, and this is true of both sexes. A thirty-year-old male still travels with his mother. When she dies, he does not go and find another group; he stays with his siblings.
This is genuinely unusual. It means a pod is not an association of adults who chose each other, and not a territory-holding unit like a wolf pack. It is one female and everyone descended from her, swimming together for as long as they all live.
What a matriline is
The basic unit is called a matriline: an older female, her sons and daughters, and her daughters' offspring. Three living generations in one travelling group is normal, four is not unheard of, and every animal in it is directly related through the female line.
Matrilines are small. A few animals to something over a dozen is the usual range, because the birth rate is low and lives are long. What people watching from a boat call a pod is often several related matrilines moving together, which is why counts vary so much between one sighting and the next.
The stability of the unit is the point. Individual orcas photographed in the same company year after year, decade after decade, is what the identification catalogues actually record, and it is how the family structure was discovered in the first place.
A group surfacing together, related through the female line
Breeding without leaving home
If nobody disperses, mating within the group would be the obvious risk. Orcas avoid it by mating when groups meet rather than within the family.
Rich feeding brings several matrilines into the same water at the same time, and those gatherings are where breeding happens. A male mates with females from another matriline and then returns to his own mother and sisters. He plays no part in raising the calf and may never see it again.
So a calf is raised entirely by its mother's family, and the family is entirely maternal. The whales in a pod share a mother, a grandmother or a great-grandmother, and the fathers are somewhere else in the ocean with their own mothers.
Genetic work on this population supports the picture: calves in a matriline are consistently fathered by males from outside it, even though those males are rarely present when the calf is growing up.
The oldest female, and what she knows
The matriarch is not a ruler in any enforcement sense. Her authority is informational. She has seen more winters than anyone else in the group, which means she has watched the herring arrive early and late, in one fjord and then in another, in good years and in failures.
In well-studied orca populations, groups follow the oldest female disproportionately when they travel, and they do so most strongly in years when food is scarce. That fits what her role appears to be: a living memory of where prey was found in conditions like these, which no younger animal has.
It also explains why females live so long after they stop having calves. An older female contributes to the group by knowing things. In a population where food moves between fjords from decade to decade, that is not a soft benefit.
Never
Neither male nor female orcas leave the group they are born into, which makes their families among the most stable social units known in any mammal.
When a matriarch dies
The loss of an old female is measurable in the survival of her descendants, and the effect falls hardest on her adult sons.
In populations where individuals have been followed for decades, the death of a mother is followed by a sharp rise in the death rate of her grown male offspring over the following year, an effect much stronger than for daughters and stronger again for older sons. A male orca who has never lived apart from his mother turns out to depend on her considerably more than his size suggests.
It is one of the reasons researchers care so much about identifying individuals rather than counting fins. A number tells you how many whales are in a fjord. A catalogue tells you that the animal missing this winter was the one the other six were following.
Watching this from a boat
None of this is visible in a single sighting, and that is worth admitting. What you see is fins, at a distance, for a few minutes.
But it changes what the fins mean. A group surfacing together is not a crowd of animals that happen to be in the same place. It is a family, with a specific oldest member, whose members have been in each other's company since birth and will be until they die.
The largest fin in a group is a mature male, and he is almost certainly travelling with his mother. Look for the animals closest to him.
And when a group splits and rejoins over the course of an afternoon, it is splitting along family lines rather than at random. The animals that leave together are the ones that were always going to leave together.
