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Off the rugged coast
of the pacific northwest,
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pods of killer whales
inhabit the frigid waters.
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Each family is able to survive here
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thanks mainly to one member,
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its most knowledgeable hunter:
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the grandmother.
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These matriarchs can live eighty years
or more,
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while most males die off
in their thirties.
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Though killer whales inhabit
every major ocean,
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until recently we knew
very little about them.
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The details of their lives
eluded scientists
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until an organization called
the Center for Whale Research
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began studying a single population
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near Washington State and
British Columbia in 1976.
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Thanks to their on going work,
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we’ve learned a great deal
about these whales,
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known as the Southern Residents.
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And the more we learn,
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the more this population’s elders’
vital role comes into focus.
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Each grandmother starts her life as a calf
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born into her mother’s family group,
or matriline.
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The family does everything together,
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hunting and playing, even communicating
through their own unique set of calls.
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Both sons and daughters spend their entire
lives with their mothers’ families.
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That doesn’t mean a young whale
only interacts with her relatives.
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Besides their own special calls,
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her matriline shares a dialect
with nearby families,
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and they socialize regularly.
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Once a female reaches age fifteen or so,
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these meetings become opportunities
to mate with males from other groups.
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The relationships don’t go much
beyond mating—
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she and her calves stay with her family,
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while the male returns to his own mother.
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Until approximately age forty,
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she gives birth every 6 years on average.
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Then, she goes through menopause—
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which is almost unheard of
in the animal kingdom.
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In fact, humans, killer whales and
a few other whales
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are the only species whose females
continue to live for years
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after they stop reproducing.
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After menopause,
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grandmothers take the lead
hunting for salmon,
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the Southern Residents’ main food source.
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Most of the winter they forage offshore,
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supplementing salmon with other fish.
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But when the salmon head towards shore in
droves to spawn the killer whales follow.
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The matriarch shows the younger whales
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where to find the most fertile
fishing grounds.
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She also shares up to 90% of
the salmon she catches.
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With each passing year,
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her contributions become more vital:
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overfishing and habitat destruction have
decimated salmon populations,
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putting the whales at near-constant
risk of starvation.
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These grandmothers’ expertise can mean
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the difference between life and death
for their families–
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but why do they stop having calves?
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It’s almost always advantageous for a
female to continue reproducing,
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even if she also cares for her existing
children and grandchildren.
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A couple unique circumstances
change this equation for killer whales.
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The fact that neither sons nor daughters
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leave their families of origin
is extremely rare—
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in almost all animal species,
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one or both sexes disperse.
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This means that as a female
killer whale ages,
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a greater percentage of her family
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consists of her children
and grandchildren,
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while more distant relatives die off.
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Because older females are more closely
related to the group than younger females,
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they do best to invest in the family
as a whole,
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whereas younger females should
invest in reproducing.
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In the killer whale’s environment,
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every new calf is another mouth to feed
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on limited, shared resources.
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An older female can further her genes
without burdening her family
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by supporting her adult sons,
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who sire calves other families will raise.
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This might be why the females have evolved
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to stop reproducing entirely
in middle age.
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Even with the grandmothers’ contributions,
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the Southern Resident killer whales
are critically endangered,
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largely due to a decline in salmon.
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We urgently need to invest in restoring
salmon populations
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to save them from extinction.
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In the long term, we’ll need more studies
like the Center for Whale Research’s.
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What we’ve learned about
the Southern Residents
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may not hold true for other groups.
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By studying other populations closely,
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we might uncover more
startling adaptations,
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and anticipate their vulnerabilities
to human interference
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before their survival is at risk.