CAN HAPPEN MORE RAPIDLY THAN WE THINK
November 10, 2013
upon a time there lived a bird that grew taller than any NBA center.
It did not live happily ever after, and the story of its demise provides
a disquieting revelation of how quickly humans can drive species to
extinction. Studies of the enormous flightless birds known as moas have
confirmed that a small number of people can eliminate a large number
of animals in a short time. The remarkable rate of extinction of the
moas is a cautionary tale for us all.
the biggest birds ever to have lived on earth, some being more than
10 feet tall. They would have towered over today's ostriches. They were
impressive ground-dwelling birds on the islands we now call New Zealand.
As would be expected, moa eggs were gigantic. I once held one that had
been obtained by the explorer Richard Archbold. A bird egg the size
of an oversized football is dramatic. But the most remarkable feature
of the one I held was that it had been laid more than 6 centuries earlier
and was just a dead egg, not a fossilized one.
late 1200s Polynesian settlers, the Maoris, arrived on New Zealand.
Maoris and moas did not mix well. By the time Columbus arrived in America,
giant moas had been extinct for a century. The reason: Maoris could
easily capture and kill the big birds. Having never encountered such
a relentless land predator, moas had never evolved the ability to fly.
rates and the level of exploitation of moas have been determined by
radiocarbon dating and the examination of Maori hunting sites with moa
remains. From this information, an estimate of 100 Maori settlers was
used to approximate the increase in human population size and rate of
habitat loss on the islands. Subsequently, mathematical models have
simulated the sequence of events for the decades following the arrival
of the Maoris.
was based on an estimated 158,000 moas living in New Zealand at the
time of human settlement. The predicted rates of decline of moas were
then determined in a variety of scenarios, with the most conservative
figures being used for each variable in order not to underestimate the
time necessary for moa extinction to occur.
time for extinction of all of the giant moas in New Zealand would have
been slightly over 150 years even without a loss of moa habitat and
with an assumption that Maoris did not eat moa eggs. However, habitat
loss did occur, and when an omelet big enough to feed a family was in
the offing, eggs undoubtedly were taken. Using the more realistic figures
that include habitat loss, the model indicates that moas became extinct
less than a century after the first Maori canoe came ashore.
is not that we can pin the loss of a fabulous group of birds on the
Maoris. Virtually all colonists in all parts of the world can be held
responsible for the elimination or severe decline of species that had
not before encountered humans as predators. The important feature is
that an original human population of only 100 people could eliminate
moas so quickly.
for us in modern times is that small numbers of humans can still eliminate
species simply by removing them from their native habitats. Exploitation
for commercial profit for the restaurant trade, the pet trade, or for
bogus medicinal cures (e.g., rhinoceros horn) can quickly bring a species
to extinction. Many of today's birds and reptiles as well as large mammals
that take several years to reach maturity and have low numbers of offspring
are unable to sustain high adult mortality rates. They can readily become
victims of human exploitation.
sent by the extinct moas is an important one: A tiny proportion of the
world's human population could eliminate one or more of our remaining
large species in the near future. We must be vigilant to prevent such
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