Resident Killer Whales: The Ocean’s Most Dedicated Mother
On Mother’s Day, many of us take the time to honor our mothers and all of the time, energy, effort, and love that has gone into raising their children.
For resident killer whales, an unnamed subspecies of killer whale found only in the North Pacific, motherly love transcends all other boundaries found in the animal kingdom. In resident killer whale society, a female’s offspring never leave her side.
This phenomenon, known as natal philopatry, is seen in many species, but killer whales take it to a whole new level. Both female AND male offspring stay with their mother for their entire lives. Natal philopatry of both sexes is very rare in mammals, being seen only in two bat species, pilot whales, and of course, resident killer whales. 
Male resident killer whales in particular are true “mama’s boys.’ While mature female killer whales will retain some degree of independence from their mothers, males are extremely dependent on their mothers. In fact, a male resident killer whale is 3.1 times more likely to die in the year following the death of his mother. For males over the age of 30, the risk of death increases over 8 times after the death of their mothers. This may be because older mothers often provision their adult male offspring. Without mom around to help feed him, a male may have more difficulty surviving. For males, having mom around also means they have higher reproductive success.  
Alaskan resident male AP10 and his probable mother, AP2.
Killer whale moms are so important that they are one of only a few species to display reproductive senescence, also known as menopause. In most animal species, a female continues to reproduce for her entire life. In killer whales, females generally stop reproducing around 40 years of age, but can easily live 30-40 years more after reproduction ceases. One main hypothesis that explains this curious aspect of killer whale biology is that elderly female killer whales are repositories of information that aid in group survival. These “grandma” killer whales are the leaders of pod movement during foraging, and their leadership is especially important in years when salmon––resident killer whales’ main prey source––is low. 
Moms are important to us all, but for killer whales, a mother is the ultimate key to survival. Without such dedicated mothers, killer whale society as we know it would likely be radically different.
Happy Mother’s Day to all mothers out there, especially the ones of the flippered variety.
For further reading, please refer to the sources under the cut.