March is Women’s History month in the United States, and this past Wednesday (March 8) was International Women’s Day. So to celebrate, I want to introduce you to a fantastic animal mother: the orca (also known as the killer whale).
Orcas (Orcinus orca) are one of the most widespread species of animals and the most widely distributed dolphin species. They are found worldwide and in every ocean, from the cold Arctic and Antarctic waters to the much warmer equator.
They’re also huge! A male orca can be 30 feet long with a 6-foot-tall dorsal fin. Females are slightly smaller but still get up to 25 feet long. Scientists can tell orcas apart by their saddle, the patch of white next to their dorsal fin. Each orca has a unique saddle patch and dorsal fin functioning like a human fingerprint that we can use to identify them.
Whale killers
The name ‘killer whale’ has existed since ancient times, when sailors saw orcas hunting and killing larger whale species. They called orcas asesina ballenas, or ‘whale killers.’ As our language evolved, we eventually flipped the order from ‘whale killer’ to ‘killer whale’ (which is apparently easier to say).
The fierceness of orcas can also be seen in their scientific name. Orcinus means ‘of the kingdom of the dead;’ orca means a kind of whale.
But while ‘killer whale’ is a popular name for orcas, it’s problematic for two reasons. First of all, orcas aren’t actually whales! They are, instead, the largest type of dolphin.
Second, while orcas are fierce predators and on the top of the oceanic food chain, ‘killer’ might be a bit extreme. They don’t go around viciously ripping whales apart, for example. And orcas are pretty discerning in what they attack for food. Most attacks on humans, for instance, have been a case of mistaken identity, with the orca thinking the human surfer is a seal. Once they realize their mistake, the orca will stop attacking. There has never been a recorded kill or full attack by an orca on a human in the wild.
However, the story is different for captive orcas. Captive orcas (like the SeaWorld orca Tilikum) have been known to attack and kill their human trainers. This aggressive behavior is almost certainly a result of stress. Orcas are highly intelligent and social creatures who dive and migrate long distances in the wild; captive orcas have much less space to swim and are kept in artificial groups or even by themselves. Living in a zoo or aquatic park is an inherently stressful place for an orca to be.
Ecotypes
Remember how orcas are found all over the world? Well, this means that orcas living in different areas have access to different types of food. This has led to different ecotypes, with different populations and pods hunting different prey species.
Because different ecotypes hunt different prey, multiple ecotypes can live in the same general geographic area. After all, without direct competition for the same food, there is plenty to go around for everyone! For example, there are three ecotypes in the North Pacific: a mammal-eating ecotype, a fish-eating ecotype, and a fish- and shark-eating ecotype found further offshore. Different ecotypes usually stay away from each other and even have physical and genetic differences.
Matrilineal
Orcas live in groups called pods that are matrilineal and led by an older female. In many orca pods, families stay together for life – their pod will contain the matriarch, her sons and daughters, and her daughter’s offspring. Larger pods may have several matrilines that stem from a common ancestor. As their mothers died, the daughters formed groups of their own that remained near each other. The oldest, grandmother female usually serves as a source of knowledge for her family, guiding them to the best places to hunt and sharing what she knows.
Orca matriarchs play a critical role in maintaining the culture of each individual pod. For example, different pods have different vocalizations to communicate with each other (like having different languages or dialects). These vocalizations are passed down through the generations.
Older females also play a role in passing down the hunting culture of a pod. Orca pods hunt like wolf packs and many have pod-specific hunting techniques. For instance, some pods will dislodge seals from ice floes, while others may reach seals by stranding themselves on the beach. But no matter the specific hunting technique, it is always taught by the older individuals in the pod.
Mama’s boy
Orca mothers spend a lot of time taking care of their sons. Male orcas are enormous, which means they a) need more food and b) are less agile, which means they may have trouble catching their own prey. So, mother orcas also spend a lot of time hunting for their sons.
In fact, male orcas are so dependent on the food their mothers share with them that they’re likely to die themselves just a year or two after their mother.
This food sharing comes at a cost to the orca mother – they will have fewer offspring overall. Compared to orcas with daughters, orca mothers with sons are much less likely to have additional offspring in future years. We can also put a hard number on it: having a son reduces the odds that a female will have a child in a given year by ~70%.
That’s a substantial reproductive cost! Why do orca mothers give so much to their sons? One potential hypothesis is that investing in sons could increase a mother’s downstream reproductive success. A female can only have one calf at a time, but a male can impregnate many females. So, by investing heavily in her son and making him a strong potential mate for other females, the mother orca is likely increasing the number of grandchildren she has. As an added bonus, the orca mother won’t need to spend time and effort raising these grandchildren because they’ll be born in different pods.
Menopause
Here’s a cool fact: orcas are one of the few animals that we know go through menopause! The others are short-finned pilot whales, belugas, narwhals, and humans. Now, this could be because few animals live long enough to have a chance to go through menopause. But even long-living animals like elephants can continue having offspring well into their 60s.
This begs the question: why do orcas go through menopause? After all, if you want to maximize your reproductive success, it doesn’t make sense to stop having offspring while you’re still alive.
Scientists have a few hypotheses. First, menopause may represent a shift from focusing on birthing offspring to ensuring your existing children have the optimal chances for survival. Remember, the oldest female in a pod is the mother or grandmother to the rest. She is in charge of guiding the pod to food sources and safety. Menopause may represent a switch in resources from birthing new calves to maintaining her family’s survival.
As a related hypotheses, orcas may go through menopause because their daughters are having calves of their own. Orcas are huge and need lots of food; it’s possible that there may not be enough food around for both mother and daughter to have calves at the same time. One study found that when multiple generations of orcas had calves simultaneously, 31% died. When deaths happened, the calves of older mothers were 1.7 times more likely to die than the younger mothers. So, instead of wasting time and energy having a calf that is more likely to die, menopause is a way for older mothers to switch their strategy to supporting their current daughters and grandchildren.
For matriarch orcas, protecting and supporting their family is a lifelong job.
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