The Mysteries of Matrilinities
Why grandmother killer whales favor their male descendants
Killer whales are apex predators, lacking natural predators of their own, and inhabit all of the worlds oceans and most of our seas. They vary broadly in behavior, diet, and communication patterns. There are three main sympatric ecotypes of killer whales present in the Pacific Northwest, known as “resident”, “transient” and “offshore” killer whales. Of these, the resident whales of the Salish sea have been by far the most heavily studied. Their prey is salmon, chinook salmon in particular, and they hunt cooperatively. The resident pods are divided into “northern residents” and “southern residents”, the latter being comprized of three pods (J, K, and L). These three pods are well researched, as their markings and distinct calls make identification extraordinarily accessible to human scientists. Orca are distinct among mammals for the long post-reprodutive life of female orca, who provides extensive parental care even after menopause. Numerous studies have shown a clear correlation between the mother’s survival and the offsprings fitness. This paper will explore the matrilinal social structures of Puget Sound’s orcas to assess the evolutionary advantages to close mother-son relations. In particular, it will examine the difference in behavior of female and male offspring upon reaching sexual maturity, and relate this to similarities or differences in parental care output from male and female killer whales. Factors to be assessed include the complex social behavior of killer whales, the importance and existence of cultural transmission across generations, stability and instabiliity in pods and sub-pods, impacts of cooperative hunting, role of post-menopausal females in the pod, and role of non-parents assisting in parental care.
The intelligence (as it can be perceived by humans) of killer whales is well-known in anecdotes and statistics, from the stories of whales taunting fishermen to the sobering amount of antidepressants given to captive orcas. It has been hypothesized that the large brain size of killer whales evolved to facilitate social responses to various environmental challenges. When deprived of social relations with other killer whales, certain individuals have displayed depression and desire to socialize with humans. In the wild, the scientific exploration of social behavior and structure within and between the resident pods has shown remarkably stable organization around matrilines, with both male and female offspring remaining with their mothers into adulthood. Whales rarely leave these small sub-pod matrilines for more than a few hours at a time, to seek copulations or forage.
Killer whales, like most delphinids, communicate extensively vocally in the water. Fish-eating killer whales communicate freely, as their prey (unlike marine mammals) cannot hear sounds in the frequencies of killer whales. The social structure of the southern...