Native cormorants? Not in Great
By Eric Sharp
Detroit Free Press
In co-evolution, living things develop strategies over
hundreds or thousands of years that let them inhabit the
same area, sometimes through mutual benefit, sometimes
through a mutual standoff.
One of the most fascinating examples I've seen is New
Zealand's lancewood tree. It grows ramrod straight to
a height of about 12 feet, with no branches and only a
few small, unappetizing leaves at the tip. Lancewood,
named for its usefulness as a spear, makes a perfect spear
shaft until it reaches that height. Then branches sprout
from the top, the leaves become much bigger and succulent,
and the trunk eventually grows as big as an oak.
Juvenile and mature lancewoods are so different that
botanists classified them as different species for more
than 100 years.
It turned out there was a reason for the spindly shape
of the young lancewood. Ten to 12 feet was about the maximum
height a giant moa bird could reach to munch leaves. Waiting
until it was above the reach of a 200-pound, flightless
moa before leafing out greatly increased the lancewood's
chances of surviving long enough to reproduce.
The moas are gone, killed off by the Polynesian Maoris
who arrived about 1,000 years ago. But lancewoods don't
know that, and without evolutionary pressure to change
they continue to produce perfect spear shafts before growing
Whether you believe it's the product of divine intervention
or cosmic accident, co-evolution is one of the most intriguing
processes in nature, and there is little more jarring
than seeing an exotic species upset the scales. That's
what has happened with the appearance of double-crested
cormorants on the Great Lakes.
The first record of these goose-sized diving birds on
the Great Lakes was on western Lake Superior about 1913.
Early white settlers didn't mention them, and we don't
find cormorant bones in the garbage dumps of prehistoric
Indians, who used about every part of every animal they
Cormorant numbers stayed low through the 1980s. Hundreds
of commercial fishermen, who saw the birds as economic
competitors, destroyed as many eggs and young as they
could on the islands where the birds nested. And DDT had
so poisoned the landscape that cormorants laid eggs with
shells so thin they were crushed by the nest-sitting parents.
Those that hatched had deformities like crossed beaks,
which prevented them from feeding.
But an end to commercial fishing and a ban on DDT brought
the cormorants back. Their numbers rose sharply in the
1990s with improvements in water quality, which resulted
in a vast increase in the number of fish that were the
perfect size for cormorant food.
In addition to wreaking havoc on fish stocks, cormorants
are destroying vegetation on the islands where many herons
and egrets nest. West Sister Island, off the Ohio shore
of western Lake Erie, draws 40 percent of all the herons
and egrets that nest on the five Great Lakes. Cormorant
numbers there have ballooned from 183 nesting pairs in
1992 to nearly 3,000 last year, while heron and egret
nests have dropped from 4,000 to about 2,200.
The cormorants are killing the trees and bushes on West
Sister and other islands because cormorant guano, or poop,
is much more acidic than egret or heron guano. I think
that alone is proof the cormorants are newcomers.
If cormorants had evolved in the Great Lakes, the trees
they nest in would have evolved to tolerate cormorant
guano, as they tolerate egret and heron guano, or they
would have developed anti-cormorant defenses, such as
big thorns or skinny branches that wouldn't support nests.
No animal that destroys its habitat will survive long.
And that leaves us with the thorny question of what to
do when one protected species threatens the survival of
In the Pacific West from whence they came, cormorants
nest mostly on rocky, treeless islands, or inland on marsh
plants that die off each winter and grow anew each spring.
Anglers are furious that government agencies have been
so slow to come up with a plan and take action. A lot
of anglers would like to be allowed to shoot cormorants,
but a hunting season isn't the answer. First, it's senseless
to hunt something you won't use, and no one will eat a
cormorant. Second, hunters couldn't kill enough to make
a real difference.
What we need is a large-scale control program in which
state and federal biologists would oil the eggs of every
cormorant nest they could reach. After a few years of
a disrupted breeding cycle, cormorant numbers should drop
to a level where they can at least be tolerated.
But government biologists don't want to be caught in
a fight between anglers and animal-rightists, who threaten
to sue if anyone musses a single feather on a cormorant.
So the need to preserve native species is a godsend for
the scientists. Now they can argue that if reducing cormorant
numbers is the only way to do so, it's one of the unfortunate
but hard truths of nature.