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Illustration by Mike
Storey |
Rise of the cormorant
By Alan Pistorius
The double-crested cormorant is much in the
news these days, and most people find it a difficult bird to admire.
An accomplished nature photographer warns us of the species’
“sinister, hawk-like visage” and “dark, greasy
plumage.” The long, snakelike neck and a vocal repertoire
restricted to grunts and croaks have inspired little poetry.
And then, of course, there is the memorable experience of the breeding
colony. No one who has ever been dumped ashore on a fine midsummer
day in the midst of hundreds or thousands of cormorant nests can
hope ever to forget the overwhelming cumulative effect of gangly
black young creatures squawking away in a nursery composed of guano-slicked
boulders, oily, fly-swarmed puddles, decaying fish remains, and
the vomited oval pellets of compacted fish bones in various stages
of decomposition. (Audubon summed up a visit to such a colony in
Labrador in his journal: “The noise was shocking and the stench
intolerable.”) Add a few hundred adult ring-billed gulls circling
and screaming—and occasionally evacuating—overhead,
and you’ve got the Four Brothers Islands in Lake Champlain.
Not a place many would choose to take the family for a summer picnic.
Most of the world’s 30 species of cormorants are strictly
coastal, foraging in salt and brackish water and nesting on cliffs
or isolated islands. Our double-crested—the moniker refers
to a double cowlick of light-colored feathers that appears briefly
on the heads of breeding birds—exploits interior fresh water
as well, and the several interior North American populations have
alternately waxed and waned in historic times, largely in response
to human persecution or lack thereof. In recent decades, thanks
to the demise of DDT and a decline in illegal shooting, the species
has been in super-wax mode, and New York and New England have been
invaded on two fronts: the Great Lakes population infiltrating from
the west and the Atlantic coast population advancing up the St.
Lawrence River from the east. The first pioneer cormorant nests
appeared on the Four Brothers in 1984. Lake Champlain has proved
a dandy host—several islands now support more than 3,000 breeding
pairs—and the rest, as we say, is history.
What, if anything, to do about this cormorant explosion is an ongoing
controversy. The knock on these birds is twofold: They kill their
breeding-island trees and eat the fish that rightly belong to fishermen.
Cormorants do, through guano deposition and twig-stripping for nesting
material, cause the early demise of their own nesting trees, which
eventually fall, leaving the birds to nest on the ground with the
gulls. To boaters accustomed to seeing treed islands, a stripped,
whitewashed island may look like hell. But my friend Mike Peterson,
who managed the Four Brothers for years, points out that new trees
(cherry, basswood, buckthorn) are already of a size to support the
nests of other species—black-crowned night-heron, cattle egret,
glossy ibis—and that there are now more species breeding on
the islands (including an impressive newcomer, Caspian tern) than
there were when cormorants first appeared. The plausible prediction
that the double-crested would crowd other birds off the islands
may have been premature.
Fishermen are always suspicious of other fish-eaters, of course,
though common loon, osprey and bald eagle are, thanks to their cachet,
typically given a pass. Like diving ducks and loons, cormorants
pursue underwater prey they can catch, mostly slow-swimming non-sport
fish. Stomach analyses of adults killed in Vermont’s control
program suggest that Champlain cormorants feed largely on perch.
(Double-cresteds elsewhere often show a particular fondness for
eels. Imagine how the birds’ local reputation would change
should they somehow learn to target lampreys!) Cormorants are not,
of course, averse to taking game fish. Should a bass or trout happen
by and prove catchable, our hook-billed pelican relative will be
happy to eat it.
Cormorant home life, if you can get comfortably upwind, is pretty
interesting. While the adults are lamentable housekeepers, they
are attentive and diligent parents. They regularly relieve one another—after
a formal greeting ceremony—during four weeks of incubation
duties on the stick and/or “seaweed” nest. Both parents
attend the three or four different-size chicks, which, naked and
blind early on, are kept warm during cool nights and shaded during
hot days, the off-duty parent carrying water to the panting young
in its bill. At first the chicks can’t handle solid food,
and instead dip into their parents’ trough-shaped lower mandibles
for regurgitated bouillabaisse. Semi-solid food follows, then fish
parts, and finally whole fish. It will be six long weeks before
the young fledge (they swim expertly before they can fly), remaining
partly dependent on the adults through the summer as they master
the cormorant skills of flying in lines, chasing fish, and loafing
on buoys and wharves and dead rowboats while hanging out their collapsed-umbrella
wings to dry. |
