(Honolulu Star-Advertiser)
Stabilizing role
speculated for elder
female pilot whales
By Susan Scott
POSTED: 01:30 a.m. HST, Apr 04, 2011
I don't know whether they have hot flashes, but
female pilot whales go through menopause.
That fact was discovered in 1984 after researchers
examined 298 bodies of short-finned pilot whales
killed for food in Japan. By using growth layers in
teeth to determine each whale's age, the scientists
learned that female pilot whales stop reproducing at
36 years of age, and their ovaries wither, yet they live
nearly 30 more years, to about 65. Male pilot whales
don't live much past 40.
This is notable because most mammals die soon after
their gonads give out. So far, only pilot whale, orca
and human females are known to live beyond their
powers of procreation.
One explanation for life after menopause is the
grandmother hypothesis, a theory that older females
help younger relatives raise their offspring. Like
people and killer whales, pilot whales also live in
genetically related family groups.
And here's some spicy food for thought (boomers take
heart): Female pilot whales continue to copulate long a
fter their ovaries quit. This, researchers speculate,
might help stabilize the pod by reducing fighting
among lusty males and/or keeping them from
wandering to other pods looking for love.
Pilot whales got my attention after several pods passed
my sailboat in the Sea of Cortez (Gulf of California).
The little 20-foot-long charmers were short-finned
pilot whales, a warm-water member of the dolphin
family. These animals' front flippers are about one-
sixth their body length.
The only other pilot whale in the world is a long-
finned species with fins about one-fourth its body
length. These whales also live in kin-based groups
but prefer the cold waters of the North Atlantic and
Southern Ocean. There are no grandma baby sitters in
these pods. In one of evolution's mysteries, long-
finned females do not live long after their ovaries stop
producing eggs.
Pilot whales are easy to identify from a boat because
they have a look and behavior all their own. The name
of their genus, Globicephala, means "globe head" and
refers to the whales' well-defined, bulbous foreheads.
In some areas these whales are called potheads.
Pilot whales got their name from the probably false
belief that a single member leads the pod, even to
death on a beach. Another source says that the term
"pilot" came from the notion that these whales guide
fishermen to a catch. This might be partially true
because pilot whales sometimes associate with
schools of herring, tuna and the whales' favorite food,
squid.
I've read that pilot whales often swim abreast of one
another, and I finally saw them do it. The whales I
spotted were swimming shoulder to shoulder at speed,
their distinct round heads and broad dorsal fins rising
up and down on the surface like black pistons. This
chorus-line behavior might increase the group's
chance of finding a school of squid.
Here in Hawaii we have our own resident population of
short-finned pilot whales. You can read about
ongoing research on our whales, and see outstanding
photos of them, at www.cascadiaresearch.
org/hawaii/shortfinnedpilotwhale.htm. It's not
possible to pick out the feisty grandmothers from
other pod members in the pictures, but I like knowing
they're there. In the world of mammals, we aging
females are not alone.
———
Susan Scott can be reached at www.susanscott.net
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