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Glossary
of Terms
Cormorant
Facts
Useful
Links
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Cormorant Facts
in
colonies on the ground or in trees; will renest.
at
3 years old
3
to 4 eggs
25-29
days
by
diving and catching fish in waters up to 25 ft. deep
in
fall to mid-Atlantic and Gulf States.
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bird’s activities while building a nest or incubating
and raising young. Cormorants prefer to nest in trees but
will nest on the ground if trees are not available. |
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bird’s activities while resting, preening or drying
themselves, generally on rocks or and sometimes in trees. |
A
bird’s activities while in transit on migratory pathways.
Local Cormorant populations swell in the spring and in the
fall, before and after nesting seasons, while Cormorants
that are nesting elsewhere migrate along Lake Champlain.
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Double-Crested Cormorants
on Lake Champlain |
The Lake Champlain Land Trust appreciates
the intrinsic value of all native species. Nevertheless,
we support legal and appropriate efforts to control nesting
cormorants
on islands on which we hold conservation easements,
when necessary to maintain balance among native species.
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| If you have any questions about
Double-Crested Cormorants that were not answered here, please
feel free to
email your question
to us at: I
have a Cormorant question. (info@lclt.org). We will be happy
to try to answer your question or direct you to a resource. |
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What Are Double-Crested Cormorants?
Double-Crested Cormorants
are migratory seabirds that spend the warm months in northern
oceans and lakes, such as the Great
Lakes and Lake Champlain, and spend the cold months in the
mid-Atlantic and Gulf States. They are large black birds, 29
to 36 inches long with a wing span of about 54 inches. They
weigh about 6 pounds. Their diet consists of small fish, which
they catch by diving and pursing under water.  |
Are Double-Crested Cormorants Native To
Lake Champlain?
Cormorants are native
to North America. The Double-Crested Cormorant is the most common
of the six North American cormorant
species. The highest numbers of Double-Crested Cormorants are
found in the Great Lakes. Cormorants were not reported on Lake
Champlain until the 1930s, and did not establish a significant
population on Lake Champlain until the 1980s. The Cormorant
population grew substantially in the 1990s, and continues to
grow at a slower rate. The Cormorant population on Lake Champlain
is expected to stabilize over time.
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Are Double-Crested Cormorants A Protected Species?
Double-Crested Cormorants
are among approximately 800 native bird species protected under
the Migratory Bird Treaty Act
of 1918. The protections of the Migratory Bird Treaty have
been adopted by the United States, Canada, Mexico, Japan and
Russia. Only authorized representatives of state and federal
governments and non-governmental organizations who hold a permit
under the Migratory Bird Treat Act may take any steps to manage
Cormorant populations. Permits may be issued to private parties
under special circumstances.
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Why Are Double-Crested Cormorants Considered
A Nuisance Species On Lake Champlain?
There are many lovely
small islands in Lake Champlain, some undeveloped and some with
one or more seasonal homes. When
Cormorants nest on an island, they use sticks and twigs from
adjacent trees and shrubs for nest materials, leaving the trees
denuded of vegetation. Nesting and roosting Cormorants also
create large quantities of guano. The guano can eventually
kill vegetation on the island and prevent new vegetation from
growing. Once Cormorants begin nesting on an island their numbers
can quickly increase making the island unsuitable for other
species such as the Common Tern, which is an endangered species
in Vermont. Denuded islands also are unsuitable for hiking,
beaching, picnicking or swimming and are often accompanied
by a strong odor from the presence of large quantities of guano.
For aesthetic reasons, some people object to seeing islands
overtaken by Cormorants and guano.
Some people believe Cormorants eat too much of the local fish
population, which is of particular concern to local residents,
conservationists, scientists, and recreational and professional
anglers. Research conducted on Lake Champlain has indicated
that Double-Crested Cormorants eat primarily yellow perch.
It is unknown whether Cormorants have a significant impact
on the population of yellow perch or any other fish in Lake
Champlain.
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What Should Landowners Do When They Find
Cormorants On their Property?
Private
individuals are not allowed to disturb Double-Crested Cormorants.
Concerned land owners can call the Vermont Department of Fish
and Wildlife at (802) 241-3000 and they will be directed to the
appropriate individual.
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What Cormorant Management Techniques Are Used By Authorized
Wildlife Authorities?
If Cormorants are
nesting on an island, population growth can be controlled by
spraying vegetable oil
on their eggs.
The oil prevents the eggs from hatching. If the Cormorants’ efforts
to hatch their offspring on a particular island are unsuccessful,
generally they will move on to another nesting area, thus sparing
the island from damage. However, this is not a short term solution,
because the Cormorants will continue to roost on the island
during the nesting season when the eggs are oiled, until they
give up on hatching the eggs. They also may continue to use
the island for roosting, even if they nest elsewhere.
Another technique is to remove the Cormorants’ nests.
While removing nests may reduce reproduction for a particular
year, the Cormorants will rebuild the nests in the same location,
or build a new nest in a new location, resulting in only
short-term impact on reproduction rates. For example, on
Rock Island in St. Albans Bay, Audubon Vermont has been removing
Cormorant nests to control Cormorants and thus protect the
Common Tern, an endangered species in Vermont.
One
of the many challenges presented in Cormorant control is
that Cormorants do not always roost
and nest in the same
location. Although Cormorants can do more damage where they
roost rather than where they nest, the most effective and humane
control measures focus on the nests. Cormorants generate quantities
of guano where they roost and can denude a roosting island
while nesting elsewhere. Keeping Cormorants from roosting on
an island requires netting the trees or otherwise making the
island unappealing for roosting, which of course also makes
it unappealing for other species as well. If the purpose of
keeping the Cormorants away is to preserve the island’s
aesthetic appeal or keep the island available for other bird
species, the techniques for stopping Cormorant roosting generally
defeat the intended purposes as well.
If Cormorants are roosting in a particular location and nesting
elsewhere, the only effective way to encourage them to roost
somewhere else is to harass them while they roost. This requires
a significant commitment of time and energy, to routinely harass
the birds when they return to roost.
Encouraging Cormorants
to leave a particular site can have unintended consequences,
however. The Cormorants
may select
another nesting or roosting site that is equally sensitive
or scenic. Also, some Cormorants may move on to another nesting
site while others remain at the current site, thereby spreading
the Cormorants to more locations on the Lake. Moving Cormorants
off of one location can cause friction with other property
owners, or even friction between states or local governments,
if one party moves the Cormorants into the other party’s
property or jurisdiction. On balance, in some cases it may
be better to allow Cormorants to colonize certain locations
rather than forcing them to move all around the region and
perhaps colonize many more locations.
Shooting Cormorants can be allowed under
federal Migratory Bird Treaty Act permits if it is demonstrated
that nonlethal
control techniques are not effective. For example, shooting
may be allowed at commercial freshwater aqua culture facilities
(fish farms) in the southeast United States, because Cormorants
are known to appear at fish farms only to gorge themselves
at feeding time while nesting and roosting in other locations.
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Do Cormorants Make Any Positive Contribution To The Local Habitat?
All native species
play a role in maintaining equilibrium in the natural environment.
Of course, if one species dominates
and there is no natural predator or dietary limit on their
population growth, imbalance can occur. At present there is
no consensus in the conservation community as to how to maintain
balance with Double-Crested Cormorants.
Let’s consider an example. The
Lake Champlain Land Trust has conserved several islands that
serve as nesting grounds
for Common Terns. Common Terns and Double-Crested Cormorants
can nest or roost on the same islands. If the Cormorant population
becomes too large or the Cormorants denude the island, the
Common Terns will move to find new nesting locations. The goal
should be to maintain balance between Common Terns and Cormorants
on any given nesting location, and thus avoid destruction of
the island habitat by the Cormorants.
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What Position Does The Lake Champlain Land Trust Take With
Regard To Cormorant Control?
As an organization
dedicated to saving habitat for migratory birds on Lake Champlain,
such
as Common Terns, the Lake Champlain
Land Trust supports the idea that Double-Crested Cormorants
are entitled to share Lake Champlain and its islands along
with other bird species. Some control measures may be necessary
to ensure that Cormorants share the Lake’s resources
rather than dominating and depleting the resources to the detriment
of other species. We work in conjunction with the Vermont Department
of Fish and Wildlife and the Audubon Vermont to determine on
a case by case basis whether Cormorant management measures
should be implemented in any given year at each island under
our management. The Lake Champlain Land Trust supports efforts to control
nesting Cormorants on islands on which we hold conservation
easements, when deemed necessary by appropriate management
authorities to maintain balance among native species on Lake
Champlain. Cormorants have established nests on four islands
on which the Lake Champlain Land Trust holds conservation easements:
Woods Island, Rock Island (Panton), and Mud Island, which are
under State management, and Rock Island (St. Albans) which
is managed by the Audubon Vermont. The Lake Champlain Land
Trust has supported efforts deemed necessary and undertaken
by the State and Audubon Vermont to control Cormorants on Rock
Island (Panton), Mud Island and Rock Island (St. Albans). On
Rock Island (Panton) and Mud Island, located near each other,
the State undertook control measures prior to 1996 and Cormorants
have not returned to those islands in subsequent years. Cormorants
only appeared on Woods Island for one nesting season and have
not returned in subsequent years, so the State has not taken
any steps to control Cormorants on Woods Island.
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Other Cormorant Resources on the Internet:
U.S.
Fish & Wildlife Service, Division of Migratory Bird
Management, Final Environmental Impact Statement of
Double-crested Cormorants
(http://migratorybirds.fws.gov/issues/cormorant/cormorant.html)
Status
of the Double-crested Cormorant (Phalacrocorax auritus) in
North America. Final Report to USFWS
http://web.tiscali.it/no-redirect-tiscali/sv2001/cormo_abstract/2001-2.htm
The
Cormorant Conundrum.
Excellent article about UVM Professor Dave Capen's approach
to cormorant control. Dave also helped found our Land Trust.
http://www.uvm.edu/outreach/main/?Page=News&storyID=5123
Double-crested
Cormorants - Description by Audubon
http://www.audubon.org/bird/BoA/F41_G1b.html
Double-crested
Cormorants - Excellent photos and description, Saltgrassflats
http://www.saltgrassflats.com/birds/cormorant_dblcrested.html
Double-crested
Cormorants - USGS, photos, descriptions, song,
and migration maps. http://www.mbr-pwrc.usgs.gov/id/framlst/i1200id.html
Double-crested
Cormorants - Natureworks
http://www.nhptv.org/natureworks/doublecorm.htm
The Rise of the Double-crested Cormorant on the Great Lakes:
Winning the War Against Contaminants. Environment Canada. http://www.on.ec.gc.ca/wildlife/fact
sheets/fs_cormorants-e.html |
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Saving Our Lakeshore and Natural Areas
Lake Champlain Land Trust One Main Street, Burlington, VT 05401 802.862.4150 or info@LCLT.org |
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