Cormorants have their place in nature's
By D. Leier
Grand Forks Herald
Published May 13, 2005
Double-crested cormorants don't get much respect these
days. While I don't expect to generate much sympathy for
the cormorant, I do wonder about the recent level of disdain
and disgust often associated with the mere mention of
this fish-eating bird's name.
Cormorants never were all that popular. While people
might speak highly of a great blue heron or pelican or
common loon - all birds that also eat fish - cormorants
seldom receive that same kind of admiration.
But the level of animosity certainly has escalated in
the last decade, during which cormorant populations all
across the Midwest have increased significantly. These
birds have become so numerous that they've been blamed
- sometimes rightly so - for reductions in fish populations
in many locales
The cormorant is just one of many natural predators that
eats some of the same fish, birds, or mammals that anglers
and hunters pursue. Great-horned owls eat pheasants. It's
hard to say if there are more owls now than 100 years
ago, but I do know the pheasant population has increased.
To blame owls for eating pheasants is like taking exception
to the guy grabbing a sofa off the boulevard during city
cleanup day, only because you wanted that gem for yourself.
The historic cormorant increase is linked to a combination
of events. Nationally, scientists point to the federal
ban on the chemical DDT as a turning point for cormorant
populations, which had dwindled into the 1970s.
In the Midwest, biologists point toward a wet cycle that
began more than a decade ago as a major factor. Since
1993 in North Dakota and other nearby states, water levels
in thousands of wetland and lake basins have increased,
flooding and killing mature trees that had grown up around
Cormorants nest and roost in bare, dead trees within
or next to water. Within a few years, cormorants had a
lot more nesting habitat available. In addition, the high
water that flooded the trees in the first place began
to support fish, so there also was much more food available.
It's a classic example of how nature's predator-prey
cycle has a built-in lag. The prey in this case is the
fish inhabiting the bodies of water. For several years,
anglers in North Dakota happily enjoyed the bounty of
dozens of "new" fisheries before the cormorants
started to become noticed as a major competitor.
Someday, when all those dead trees finally fall to the
ground and those flooded water basins shrink, the cormorant
population will decline naturally. In the meantime, there
are considerable ongoing discussions about whether people
should step in and begin cormorant population control
Heart of the matter
Cormorants eat fish like a deer eats alfalfa. One study
showed a single cormorant can eat a dozen fish in a day.
While cormorants would be hard pressed to swallow the
same size fish that anglers typically target, they can
eat a whole bunch of smaller fish. And they don't differentiate
if the fish is a walleye fingerling, next year's keeper
perch or a fathead minnow. A study in Minnesota showed
cormorants do feast on walleye and perch, but also in
the diet are less desirable species, namely eelpout and
Cormorants influence more than just fish and fish populations.
Their colonies are known to exclude other bird populations
that rely on the same type of habitat, and there even
are concerns in some areas of the United States that cormorants
could be detrimental to federally threatened or endangered
Cormorants are migratory birds under protection of the
U.S. Fish and Wildlife Service. The North Dakota Game
and Fish Department has petitioned the service, so far
unsuccessfully, for broader tools for decreasing the cormorant
Some groups have called for cormorant population reduction
via shooting in areas where dozens, if not hundreds, of
these birds congregate to feed. Fish and Wildlife Service
research in the Great Lakes region has shown that cormorants
will avoid such danger by just moving to another area
where they are not harassed. While that might immediately
reduce pressure on an individual body of water, control
measures over an entire region would be necessary for
effective population reduction.
Am I an advocate for the cormorant? Not necessarily,
but they do have a place in the world.
And that place may be the same secret fishing spot to
which you're headed, for the same reason: To catch some
Leier is a biologist for the North Dakota Game and Fish
Department. Contact him at firstname.lastname@example.org.