Saturday, January 26, 2008

Clam Shell Mystery

Until we moved to Rhode Island last year I had never before lived by the sea. So there are many things that I am still learning about life on the shore, and some things that are still a mystery to me. Perhaps one of my readers with more knowledge of the littoral environment can answer a question that's bugging me today....

This morning I went for a run around Bristol Harbor, starting from Independence Park, up the East Bay Bike Path for a short way, along Poppasquash Road around the head of the harbor, past Bristol Yacht Club and then further down the road towards Poppasquash Point. Not surprisingly on a frigid January day there was little activity in the harbor, though there was one yacht on a mooring, and I saw some Lasers being rigged near the Herreshoff Museum. But Laser sailors are crazy anyway.

Where was I? Oh yes. The great Clam Shell Mystery.

The bike path was littered with broken shells, clams I think, and the unmistakable white splashes indicating seagull activity. I'm 99% certain that what's been happening is that the gulls have worked out that dropping the clams from a great height on to the path is the easiest way to break the shells and gain access to the meat inside. The same thing used to happen at my old frostbiting club on Long Island Sound where, at the end of the winter, the parking lot was covered in broken shells.

But I've never seen this phenomenon in the summer. Why not? Is there a different breed of gulls with different habits here in the winter? Are the clams harder to prise from their shells in the winter? Do seagulls only eat shellfish when there's an R in the month? Or do the gulls have access to other food in the summer and only resort to clams in the winter? What's the answer?

The Google didn't help me much in trying to find an answer. But it did turn up this post Seagull Smarts by a fellow Rhode Islander who claims to know a bit about science and the environment. He spotted the same phenomenon (maybe on the same bike path) and it spurred him to ponder how smart seagulls are and the role of genetics and evolution in their discovery of this natural clam-opener.

But I'm still mystified as to why we only see this in the winter. Somebody please shed some light on this.


Carol Anne said...

The seagulls we have in New Mexico are the epitome of laziness. If there's food to be had easily (i.e. handouts from humans), they're not going to go to the effort of diving into the water for fish or taking shellfish up into the air to drop and break the shells.

But if there aren't any easy pickings, they'll do the hard work.

Anonymous said...

Way back (>30 yrs) when we lived in Wickford, the gulls would use the roof of our building. We got used to hearing the impact, and occasionally the sound of an unbroken shell rolling. Never correlated it with the season, though.

Tillerman said...

I'm beginning to think that the most likely answer to my question was the one I proposed last and also suggested by Carol Anne - the gulls just have access to easier pickings in the summer in that particular area which is near to a couple of seafood restaurants where folk dine outside when it's warm.

fracisco said...

The seagulls in L.A. do the same thing in the winter time. There is a jetty that runs along the main entrance to the harbor of Marina del Rey, and on the top of the harbor is the bikepath, and in the winter on the bike path are hundreds if not thousands of shards of mussel shells.

And yes, a piece of mussel shell is capable of piercing your road bike innertube through the tire and a Mr Tuffy tire liner.

In a pack of 50 cyclists, there are bound to be at least 10% that will pull over to fix a flat on a winter day in L.A.

Brian said...

I had the misfortune of seeing this activity firsthand during the summer. A clam managed to find my windshield (windscreen, to you) while crossing from LBI to the mainland down in NJ. Needless to say, a new windshield was put in shortly thereafter. The amazing thing is the fact that my Laser was on the roof, extending well over the windshield and hood.

At least it didn't hit my boat!

Tillerman said...

Ahah, more evidence. So fracisco has noticed that the "broken shells on the bike path" is also a winter-only phenomenon in LA. But the winter climate in LA sure is different from a New England winter.

As I recall the harbor at Marina del Rey has some restaurants too. Do they also provide easy pickings for the seagulls in the summer months only, I wonder?

Brian's experience effectively disposes of one theory that I had, that perhaps the seagulls don't use parking lots and road and bike paths in the summer because they are too busy with people and traffic. But seagulls seem to be quite happy coming very close to humans and I didn't imagine that they would not drop their shells just because of the presence of a few bikers, or of Brian cartopping his Laser.

However, if the Carol Anne easy pickings theory is correct, why was Brian's new Jersey seagull eating clams in the summer?

It's a mystery.

Carol Anne said...

The freshwater clams at Elephant Butte are tiny and therefore hold very little nutritive value in comparison to the energy expended by the seagull in the effort of carrying them up into the air and dropping them, so they are therefore definitely the food of last resort -- if human handouts and/or trash aren't available, catching fish takes more energy but provides a better ratio of calories gained to calories expended.

On the other hand, maybe New Jersey clams are especially plump and calorie-dense, so the seagulls get a better return on their energy expenditures, even in the summer.

Still, it IS hard to imagine that dropping clams on pavement is easier than begging or scrounging off humans. Maybe there are some noncomformist seagulls in New Jersey that prefer bucking the trend.

Or maybe that particular seagull just had it out for Brian.

Anonymous said...

Do the clams only wash up on the beach during the winter ? Recently in Florida I noticed many more clams then usual washed up on the beach. I then witnessed multiple different Sea Gulls exhibiting this very same behavior a few weeks back. They will fly the clams high and dropped them on the beach. Then they would peck at the now broken shell. They may have been some other shell living creature , because the shells had long sharp looking points. Another group of people where walking by as I was watching this and they almost got a direct hit. I tried to film the behavior but my phone did not save it right. Shame :(

Anonymous said...

I live in Bristol, ride the path all the time and have suffered several clam shell flats over the years. My theory is that because people are always on the path in summer, seagulls seek less busy places to drop their clams. In winter they have it all to themselves. They love the Sip n' Dip parking lot next to the path in any season.

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