Here in BC the Northwestern Crows eat bivalves by dropping them on
the roads, sidewalks, rocks, whatever's a hard surface. There have
been studies done regarding this behavior and it's quite the thing
to watch. It's also a great way to collect shells...a few times I've
seen a crow drop one and run over and nabbed it (they often take a
few drops before the shell breaks). I've also narrowly escaped being
the accidental target of these drops as well. Quite entertaining!

Peter Egerton,
Vancouver, Canada


At 11:56 AM 1/29/01 -0500, you wrote:
>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
>
>*~*~*~*~*~*~*~*~*~*~*~*~*~*~
>Sarah R. Watson
>Curatorial Assistant
>Dept. of Malacology
>Academy of Natural Sciences
>*~*~*~*~*~*~*~*~*~*~*~*~*~*~
>http://www.geocities.com/scalaria
>
>
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Peter Egerton, Vancouver, British Columbia, Canada
Collector of worldwide Mollusca, lifetime student
of zoology and computers.
E-mail: [log in to unmask]
Step into my website:
http://www.intergate.ca/personal/seashell/index.html
(includes "Seashells of British Columbia", links and my resume)
        -Links to add, remove, alter?  Just ask!
        -This is an on-going project.
        -Suggestions always welcome :-)
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