Gulls Find New Way To Eat Clams

By SONJA BARISIC
.c The Associated Press


JAMESTOWN, Va. (AP) - The herring gull scoops a clam out of a muddy creek,
flies 200 yards to a road, rises a few feet higher, opens its bill and bam! -
the clam hits the pavement.

That scene is repeated, sometimes hundreds of times a day during the winter,
as herring gulls on Jamestown Island near Williamsburg use the road to crack
open the hard shells so they can retrieve and eat clam meat.

``They are quite resourceful,'' said Daniel A. Cristol, an assistant
professor of biology at the College of William and Mary, who has been
studying the gulls for five years.

``The long-term question is: How do they get good at it?'' Cristol said as he
stood along the road, watching the gulls on a bracing, sunny day. ``Is it a
learned thing, or is it something that evolved long ago, somewhere else, and
they just appropriated it here?''

Cristol said the skill could be innate, but his preliminary findings suggest
that the behavior is consistent with learning - an example of how some
animals are able to adjust their lifestyles when people alter their habitats.

Of the five species of gulls present on Jamestown Island during the winter,
only herring gulls drop clams.

``I think herring gulls have the capacity to learn how to do it and the
others don't,'' Cristol said. ``They learn it from one another.''

The gulls do this about two hours a day during low tide, from late November
through late March.

They use the road leading to Jamestown Island, which is littered with pieces
of clam shell, and also the hard surface of a small island in the creek
believed to be the remains of a Civil War-era bridge. The road is better,
though, because too many gulls - including the other species - lie in wait on
the bridge, ready to steal the meat when a clam is dropped.

Cristol and his students collected and measured about 6,000 clam shells over
three years, and it appears that the gulls favor a middle-sized clam, about 3
inches across.

Cristol speculates that a small shell isn't worth the energy required to drop
it because it doesn't contain much meat, while a large clam is meatier but
too heavy to carry.

Cristol also has noticed that the gulls usually rise up in the air a few feet
before they drop the clams. He thinks they are trying to reach the most
efficient dropping height. Too low, and the clam won't break; too high, and
the bird is wasting energy.

The birds seem to get better at gauging the right clam size and height as
they age, Cristol said.

Cristol did similar research with crows and walnuts in California when he was
a postdoctoral fellow at the University of California, Davis.

Crows were dropping walnuts onto roadways, and some people thought this was
an intelligent act because it looked like the crows were deliberately using
moving vehicles as nutcrackers.

Cristol and fellow researchers observed hundreds of crows and concluded that
the birds were simply dropping nuts onto any available hard surface to try to
break them open.

Still, Cristol wondered if the crows had inherited the dropping technique or
learned it from other crows. He brought that question with him when he came
to William and Mary in 1996 and continued his research with herring gulls.

In a way, the gulls are better to study because their age can be determined
by the color of their plumage, which changes from brown to white. Crows
remain the same color.

``If he can age the gulls, he can track how gulls learn, or at least get
started on that,'' said Peter Smallwood, a behavioral ecologist and assistant
professor of biology at the University of Richmond.

``His ability to age the gulls can help in trying to understand how do gulls
get so good at this,'' Smallwood said. ``Is it instinctual? Are they able to
use their experience to hone in on it by trial and error, or do they learn
from each other?''

Cristol wonders whether the gulls have a mechanism for learning by observing
other members of their species. Only a few instances of such so-called
``social learning'' have been documented.

One of the most famous examples is that of the Japanese macaque monkeys, also
known as snow monkeys. In the early 1950s in Japan, researchers gave sweet
potatoes to a group of macaque monkeys. Imo, a young female, washed her
potato in a stream before eating it.

Other monkeys began washing their potatoes as well, and today, potato washing
among the monkeys is common. Some think that proves that the animals can pass
their cultural traditions to new generations.

On the Net:

Cristol: http://www.wm.edu/biology/Cristol.html

U.S. Geological Survey, on herring gulls:
http://www.pif.nbs.gov/bioeco/herrgull.htm

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Sarah R. Watson
Curatorial Assistant
Dept. of Malacology
Academy of Natural Sciences
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http://www.geocities.com/scalaria